Academic literature on the topic 'Flagellati'

The number and location of flagella, bacterial organelles of locomotion, are species specific and appear in regular patterns that represent one of the earliest taxonomic criteria in microbiology. However, the mechanisms that reproducibly establish these patterns during each round of cell division are poorly understood. FlhG (previously YlxH) is a major determinant for a variety of flagellation patterns. Here, we show that FlhG is a structural homolog of the ATPase MinD, which serves in cell-division site determination. Like MinD, FlhG forms homodimers that are dependent on ATP and lipids. It interacts with a complex of the flagellar C-ring proteins FliM and FliY (also FliN) in the Gram-positive, peritrichous-flagellated Bacillus subtilis and the Gram-negative, polar-flagellated Shewanella putrefaciens. FlhG interacts with FliM/FliY in a nucleotide-independent manner and activates FliM/FliY to assemble with the C-ring protein FliG in vitro. FlhG-driven assembly of the FliM/FliY/FliG complex is strongly enhanced by ATP and lipids. The protein shows a highly dynamic subcellular distribution between cytoplasm and flagellar basal bodies, suggesting that FlhG effects flagellar location and number during assembly of the C-ring. We describe the molecular evolution of a MinD-like ATPase into a flagellation pattern effector and suggest that the underappreciated structural diversity of the C-ring proteins might contribute to the formation of different flagellation patterns.

SummaryThe pathogenic flagellate Blastocrithidia triatomae disrupts the digestion of Triatoma infestans; the midgut ultrastructure of bugs infected with the flagellate and of uninfected bugs is compared. Third or fourth instar larvae were dissected either unfed or 1 week after feeding.In all uninfected bugs extracellular membrane layers (e.m.l.) covered the apical microvillar border of the epithelial cells. Some midgut regions of bugs infected with B. triatomae appeared normal but often adjacent cells showed pathological effects. In affected cells the e.m.l. and the microvilli and finally the cells themselves were reduced or destroyed. Correlated with these observations of pathogenicity the method of attachment of parasites changed. When the e.m.l. were present only rarely were flagella found, but on extracellular membrane-free cells B. triatomae attached by flagellar enlargement to the microvillar border or, if this was reduced, to the apical host cell membrane. No hemidesmosome-like plaques were found at the attachment site. Although some flagella were inserted into the apical region of the cells no intracellular flagellates were observed.

Unicellular flagellated protists are a key element in aquatic microbial food webs. They all use flagella to swim and to generate feeding currents to encounter prey and enhance nutrient uptake. At the same time, the beating flagella create flow disturbances that attract flow-sensing predators. Protists have highly diverse flagellar arrangements in terms of number of flagella and their position, beat pattern, and kinematics, but it is unclear how the various arrangements optimize the fundamental trade-off between resource acquisition and predation risk. Here we describe the near-cell flow fields produced by 15 species and demonstrate consistent relationships between flagellar arrangement and swimming speed and between flagellar arrangement and flow architecture, and a trade-off between resource acquisition and predation risk. The flow fields fall in categories that are qualitatively described by simple point force models that include the drag force of the moving cell body and the propulsive forces of the flagella. The trade-off between resource acquisition and predation risk varies characteristically between flow architectures: Flagellates with multiple flagella have higher predation risk relative to their clearance rate compared to species with only one active flagellum, with the exception of the highly successful dinoflagellates that have simultaneously achieved high clearance rates and stealth behavior due to a unique flagellar arrangement. Microbial communities are shaped by trade-offs and environmental constraints, and a mechanistic explanation of foraging trade-offs is a vital part of understanding the eukaryotic communities that form the basis of pelagic food webs.

The supposedly primitive prasinophyte Pseudoscourfieldia marina has been established in culture and examined in detail. The cells swim by means of two unequal but parallel posterior flagella. Pseudoscourfieldia differs from other green flagellates in the structure of the flagellar root system, possession of a conspicuous leaflike attenuated extension from one basal body into the cell, the structure of the pyrenoid, which is invaginated by long extensions from the mitochondrial complex, and the structure of the scaly covering on the body. Pseudoscourfieldia shows distinct similarities to Nephroselmis, which is laterally biflagellate, and to the Tetraselmis group, which possesses four anterior flagella. The attachment of the hair scales on the flagella has been examined in detail for the first time in a green flagellate. The very short hair scales attach to the flagellar surface between each pair of longitudinal rows of scales known as Melkonian's rows, associated with the inside of every third scale in one row. This is probably a feature common to all prasinophytes with Melkonian's rows. Based on the many investigations now published, a classification for the prasinophytes, supposedly some of the most primitive green algae, is suggested. One class, two orders, and four families are recognized and defined, with 15 genera.

ABSTRACT The changes in motility, chemotactic responsiveness, and flagellation of Rhizobium meliloti RMB7201, L5-30, and JJ1c10 were analyzed after transfer of the bacteria to buffer with no available C, N, or phosphate. Cells of these three strains remained viable for weeks after transfer to starvation buffer (SB) but lost all motility within just 8 to 72 h after transfer to SB. The rates of motility loss differed by severalfold among the strains. Each strain showed a transient, two- to sixfold increase in chemotactic responsiveness toward glutamine within a few hours after transfer to SB, even though motility dropped substantially during the same period. Strains L5-30 and JJ1c10 also showed increased responsiveness to the nonmetabolizable chemoattractant cycloleucine. Cycloleucine partially restored the motility of starving cells when added after transfer and prevented the loss of motility when included in the SB used for initial suspension of the cells. Thus, interactions between chemoattractants and their receptors appear to affect the regulation of motility in response to starvation independently of nutrient or energy source availability. Electron microscopic observations revealed that R. meliloti cells lost flagella and flagellar integrity during starvation, but not as fast, nor to such a great extent, as the cells lost motility. Even after prolonged starvation, when none of the cells were actively motile, about one-third to one-half of the initially flagellated cells retained some flagella. Inactivation of flagellar motors therefore appears to be a rapid and important response ofR. meliloti to starvation conditions. Flagellar-motor inactivation was at least partially reversible by addition of either cycloleucine or glucose. During starvation, some cells appeared to retain normal flagellation, normal motor activity, or both for relatively long periods while other cells rapidly lost flagella, motor activity, or both, indicating that starvation-induced regulation of motility may proceed differently in various cell subpopulations.

ABSTRACT Helicobacter pylori uses flagellum-mediated chemotaxis to promote infection. Bacterial flagella change rotational direction by changing the state of the flagellar motor via a subcomplex referred to as the switch. Intriguingly, the H. pylori genome encodes four switch complex proteins, FliM, FliN, FliY, and FliG, instead of the more typical three of Escherichia coli or Bacillus subtilis. Our goal was to examine whether and how all four switch proteins participate in flagellation. Previous work determined that FliG was required for flagellation, and we extend those findings to show that all four switch proteins are necessary for normal numbers of flagellated cells. Furthermore, while fliY and fliN are partially redundant with each other, both are needed for wild-type levels of flagellation. We also report the isolation of an H. pylori strain containing an R54C substitution in fliM, resulting in bacteria that swim constantly and do not change direction. Along with data demonstrating that CheY-phosphate interacts with FliM, these findings suggest that FliM functions in H. pylori much as it does in other organisms.

ABSTRACTCurrent knowledge regarding the mechanism that governs flagellar motor rotation in response to environmental stimuli stems mainly from the study of monotrichous and peritrichous bacteria. Little is known about how two polar flagella, one at each cell pole of the so-called amphitrichous bacterium, are coordinated to steer the swimming. Here we fluorescently labeled the flagella ofMagnetospirillum magneticumAMB-1 cells and took advantage of the magnetically controllable swimming of this bacterium to investigate flagellar rotation in moving cells. We identified three motility behaviors (runs, tumbles, and reversals) and two characteristic fluorescence patterns likely corresponding to flagella rotating in opposite directions. Each AMB-1 locomotion mode was systematically associated with particular flagellar patterns at the poles which led us to conclude that, while cell runs are allowed by the asymmetrical rotation of flagellar motors, their symmetrical rotation triggers cell tumbling. Our observations point toward a precise coordination of the two flagellar motors which can be temporarily unsynchronized during tumbling.IMPORTANCEMotility is essential for bacteria to search for optimal niches and survive. Many bacteria use one or several flagella to explore their environment. The mechanism by which bipolarly flagellated cells coordinate flagellar rotation is poorly understood. We took advantage of the genetic amenability and magnetically controlled swimming of the spirillum-shaped magnetotactic bacteriumMagnetospirillum magneticumAMB-1 to correlate cell motion with flagellar rotation. We found that asymmetric rotation of the flagella (counterclockwise at the lagging pole and clockwise at the leading pole) enables cell runs whereas symmetric rotation triggers cell tumbling. Taking into consideration similar observations in spirochetes, bacteria possessing bipolar ribbons of periplasmic flagella, we propose a conserved motility paradigm for spirillum-shaped bipolarly flagellated bacteria.

Identification of Salmonella serotypes is based on flagellar and somatic antigens. The absence of flagella may consequently affect complete identification of the serotype; here it is shown that Salmonella enterica serovar Typhimurium exhibits morphological differences dependent on the peptone constituents of the culture medium. Aflagellate salmonella were produced in certain media where the nutritional ingredient was casein-based peptone or gelatin-based peptone; in gelatin-based peptone, aggregates of salmonella were observed. However, in media containing soy-based peptone as the primary nutrient, salmonella displayed a normal flagellated morphology. Transfer of aflagellate salmonella from nutritionally poor media, with casein- or gelatin-based peptone, into rich nutrient broth allowed flagella synthesis, indicating that the aflagellate form is still able to produce flagella. Amino acid sequencing of the peptones producing aflagellate organisms showed a relatively low tyrosine concentration: only 0·03±0·01 g l−1 for gelatin-based buffered peptone water, compared to 0·21±0·01 for soy-based buffered peptone water. Tyrosine is essential for flagellin, which is the subunit of the salmonella flagellar filament. The addition of 200 μM tyrosine to casein-based peptone media produced flagellate salmonella; 2 mM glucose was needed in addition to tyrosine to achieve a similar morphology in gelatin-based media. Therefore, culture media containing less than 1·20 g tyrosine l−1, and of limited carbohydrate source, when used for serological testing of clinical isolates, may result in an incomplete serological identification.

Certain fimbriae and the flagellae of Salmonella enterica serovar Typhimurium have been shown to contribute to attachment and invasion of gut epithelium in the murine typhoid infection model and to contribute to pathogenesis in the chick. However, little is known of the role these organelles play in Enteritidis poultry infections and, to study this, day-old chicks were dosed orally in separate experiments with defined multiply afimbriate and/or aflagellate mutant strains of Enteritidis. The colonization and invasion characteristics of each mutant were compared with those of the isogenic wild type strain by the determination of the number of bacteria recovered from livers and spleens at known time points post infection. Compared with wild type Enteritidis, a mutant unable to express flagella but retaining the genetic potential to express fimbriae was recovered post mortem from livers and spleens in significantly reduced numbers compared to the isogenic wild-type at all time points post infection (P<0·001). Conversely, a flagellate but multiply afimbriate mutant (defective for the elaboration of five different fimbrial types) and a flagellate but non-motile ‘paralysed’ mutant were recovered from livers and spleens in similar numbers to the wild-type. The data suggested that Enteritidis flagella, but not fimbriae, played an important role in pathogenesis in the chick model and that the flagellar apparatus itself and not motility per se contributed significantly to this role.

Flagella-driven motility is an important trait for bacterial colonization and virulence. Flagella rotate and propel bacteria in liquid or semi-liquid media to ensure such bacterial fitness. Bacterial flagella are composed of three parts: a membrane complex, a flexible-hook, and a flagellin filament. The most widely studied models in terms of the flagellar apparatus are E. coli and Salmonella. However, there are many differences between these enteric bacteria and the bacteria of the Pseudomonas genus. Enteric bacteria possess peritrichous flagella, in contrast to Pseudomonads, which possess polar flagella. In addition, flagellar gene expression in Pseudomonas is under a four-tiered regulatory circuit, whereas enteric bacteria express flagellar genes in a three-step manner. Here, we use knowledge of E. coli and Salmonella flagella to describe the general properties of flagella and then focus on the specificities of Pseudomonas flagella. After a description of flagellar structure, which is highly conserved among Gram-negative bacteria, we focus on the steps of flagellar assembly that differ between enteric and polar-flagellated bacteria. In addition, we summarize generalities concerning the fuel used for the production and rotation of the flagellar macromolecular complex. The last part summarizes known regulatory pathways and potential links with the type-six secretion system (T6SS).

2012/2013
Heterotrophic nanoflagellate (HNF) grazing is one of the major source of prokaryotic mortality in marine ecosystems, acting as a strong selection pressure on communities. Protozoans may thus affect prokaryotic abundance and alter the diversity and the taxonomic composition of the prey community, as individual prokaryotes can develop distinct grazing-resistant mechanisms. Moreover, the microbial loop is well known to regulate carbon fluxes in surface marine environments but few studies have quantified the impact of HNF predation on prokaryotes in the dark ocean. The present work was aimed to: (1) quantify the impact of HNF predation on the deep prokaryotes biomass; (2) investigate if and how prey diversity varies in response to different predation pressure; (3) define taxonomic community composition in studied areas and identify most affected prokaryotic phylotypes by HNF grazing (4) evaluate the effects of small HNF (<3 µm), which are known to dominate nano-sized compartment and represent the main bacterivores in aquatic ecosystems, being an important link between bacteria and larger protists; (5) evidence differences in community sensitivity to grazing between surface and mesopelagic ecosystems (6) identify the main environmental drivers shaping microbial community diversity. Predation experiments were performed with surface and mesopelagic water samples collected from the Southern Adriatic and Northern Ionian basins. An additional predation experiment was set up in the North-eastern Adriatic Sea. We coupled the traditional ‘dilution method’ with high-throughput molecular analysis (ARISA and Ion Torrent/454 sequencing) to provide a quantitatively and qualitatively evaluation of the grazing process occurring in marine microbial communities. The present work is structured by four manuscripts in preparation and one manuscript already submitted. 1. Heterotrophic nanoflagellate grazing on picoplankton in deep waters (manuscript in preparation) 2. Effects of heterotrophic flagellate predation on bacterial community diversity (manuscript in preparation) 3. HNF grazing impact on taxonomic composition of marine prokaryotic community (manuscript in preparation) 4. Environmental drivers structuring surface and deep bacterial communities in Adriatic and Ionian Seas (manuscript in preparation) 5. Biodiversity changes of bacterial community under predation pressure analyzed by 16S rRNA pyrosequencing (manuscript submitted) My PhD research led to important progresses in the comprehension of microbial dynamics regulating carbon cycles and bacterial diversity in the Adriatic and Ionian basins. Prokaryotic abundance and biomass were one order of magnitude higher in the photic than in the aphotic layers of Southern Adriatic and Ionian Seas (surface biomass 1.68 ± 1.76 µC L-1, deep biomass 9.00 ± 2.11 µC L-1). The Northern Adriatic community presented the highest biomass value (57.46 µC L-1), according to its richer trophic status. All in situ communities displayed the same evenness, being dominated by rare phylotypes. Rare taxa were confirmed to represent the major contributors of microbial communities, with only a few phylotypes dominant. Mesopelagic bacterial communities were as rich and variable as surface assemblages, despite the significant biomass decrease along the water column. Natural archaeal assemblages were characterized by very low richness as we recovered only two genera (Cenarchaeum and Nitrosopumilus), while in situ bacterial communities were composed by the six major marine phyla (Proteobacteria, Cyanobacteria, Bacteroidetes, Actinobacteria, Firmicutes and Deinococcus-Thermus), whose contribution varied according to sampling depth. Flagellates were demonstrated to efficiently control their preys (ingestion rates: 7.86-22.26 µg C L-1 in surface experiments, 0.53-10.61 µg C L-1 in deep experiments), causing important losses in the potentially produced prokaryotic biomass. Despite picoplankton and HNF abundance reduction with depth contrasts with the hypothesis that at least 108 picoplanktonic cells L-1 are necessary to sustain HNF community, our data confirm that also in mesopelagic waters prey and predator concentrations are sufficient to sustain efficient microbial food webs. HNF grazing modified bacterial community diversity in both surface and deep marine systems but with different strength. Mesopelagic communities were more sensitive to grazing impact, evidencing a bell-shaped response to the increasing ingestion rates. Moderate-high top-down control preserved or enhanced bacterial diversity, that fell at low predation. In upper communities grazing did not induce wide variations of bacterial richness and evenness, revealing to be more stable. Small HNF (<3 µm) were the dominant size fraction within flagellate communities and likely constituted the main bacterivores. After the removal of large HNF, a higher fraction of prokaryotic phylotypes was affected. Larger protists partially reduced small flagellate impact on their preys. Larger HNF had a more important role in photic systems compared to mesopelagic waters. The fraction of bacterial taxa favored or affected by predation when small HNF were the only predators more markedly varied in surface experiments, while few phylotypes changes their behavior between the two size treatments in deep experiments. Some taxa were consumed mainly by larger HNF (3-10 µm), while others were grazed by smaller ones (<3 µm). Over 50% of the predated phylotypes belonged to the rare biosphere, mainly in the surface experiments. Rare bacteria are thus not only a dormant ‘seed bank’ but constitute a fundamental component of microbial food webs and actively vector the carbon transfer toward higher trophic levels, being as important as dominant organisms. Although general patterns applicable to all communities were not found, trends of selectivity over different phylotypes were highlighted within sampling layer along the water column and between different systems. While the majority of predator-prey interactions were characteristic to specific environments, some can be considered common to different systems (e.g. Burkholderiaceae and Pseudomonadaceae were exclusively selected in all mesopelagic sites, Bacterivoracaceae were subjected to small HNF predation independently from sampling site or depth). The Southern Adriatic and Ionian basins were significantly distinguished by both the physicochemical water characteristics and the prokaryotes and protists abundance distributions. Cluster analysis based on Jaccard and Bray-Curtis metrics evidenced that depth and geographical location of sampling sites influenced bacterial community similarity. The Southern Adriatic Sea was clearly distinguished from the Ionian Sea. The Northern Adriatic samples were always separated from the others, coherently with different biotic and abiotic characteristics of the sub-basin. Additionally, temperature, chl a and O2 concentration represented important environmental drivers shaping biodiversity of bacterial communities that inhabit Adriatic and Ionian basins. In conclusion, we evidenced that heterotrophic flagellates control bacterial biomass and select certain taxa among all possible preys, grazing also on the rare ones. HNF predation thus shapes bacterial community structures, which in turn influence the ecosystem functioning. Despite the cell abundance decrease of both predators and preys reduces encounter probabilities, the dark ocean hosts complex microbial food webs, structured around three trophic levels (i.e. prokaryotes, small and large heterotrophic flagellates).
I nanoflagellati eterotrofi (HNF) costituiscono una delle principali cause di mortalità dei procarioti in ambiente marino, esercitando una forte selezione sulle comunità predate. Possono modificarne l’abbondanza cellulare e alterarne la diversità e la composizione tassonomica, in quanto le diverse specie procariotiche possono sviluppare distintivi meccanismi di resistenza alla predazione. Mentre l’impatto degli HNF sui procarioti degli acque marine superficiali è ben noto, pochi studi si sono focalizzati sullo studio degli ambienti profondi. Il presenta lavoro di dottorato è stato finalizzato a: (1) quantificare l’impatto della predazione da parte degli HNF sulla biomassa procariotica profonda; (2) capire se e come la biodiversità della comunità predata vari in risposta alla diversa pressione di predazione; (3) definire la composizione tassonomica delle comunità presenti nell’area di studio e identificare i filotipi maggiormente colpiti dalla predazione da parte degli HNF; (4) valutare il contributo dei piccolo flagellati (<3 µm), i quali costituiscono la più abbondante frazione nanoplanctonica e rappresentano i principali organismi batterivori negli ambienti acquatici; (5) evidenziare possibili differenze nella risposta alla predazione tra comunità procariotiche che vivono in acque superficiali e profonde; (6) identificare i principali fattori ambientali che modulano la diversità delle comunità microbiche. Esperimenti di predazione sono stati condotti su campioni di acqua superficiale e mesopelagica raccolti nel Mar Adriatico meridionale e nel Mar Ionio settentrionale. Un ulteriore esperimento è stato condotto nel Mar Adriatico nord-orientale. Il tradizionale metodo delle diluizioni è stato abbinato ad analisi molecolari quali elettroforesi capillare (ARISA) e sequenziamento (Ion Torrent e 454) per consentire una valutazione quali-quantitativa degli effetti della predazione sulle comunità microbiche marine. La presente tesi è costituita da quattro articoli in preparazione e un articolo già sottomesso: 1. Heterotrophic nanoflagellate grazing on picoplankton in deep waters (articolo in preparazione) 2. Effects of heterotrophic flagellate predation on bacterial community diversity (articolo in preparazione) 3. HNF grazing impact on taxonomic composition of marine prokaryotic community (articolo in preparazione) 4. Environmental drivers structuring surface and deep bacterial communities in Adriatic and Ionian Seas (articolo in preparazione) 5. Biodiversity changes of bacterial community under predation pressure analyzed by 16S rRNA pyrosequencing (articolo sottomesso) La ricerca condotta durante il mio dottorato ha portato a interessanti progressi nella comprensione delle dinamiche microbiche che regolano i cicli del carbonio e la diversità batterica nei bacini adriatico e ionico. L’abbondanza e la biomassa delle comunità procariotiche superficiali è risultata un ordine di grandezza superiore rispetto alle comunità profonde in Mar Adriatico meridionale e Mar Ionio (biomassa superficiale 9.00 ± 2.11 µC L-1, biomassa profonda 1.68 ± 1.76 µC L-1). La comunità descritta nel Mar Adriatico settentrionale è caratterizzata dai valori più elevati di biomassa (57.46 µC L-1), coerentemente con l’eutrofia del bacino. I flagellati eterotrofi hanno causando perdite significative nella biomassa procariotica in tutti gli esperimenti condotti, con tassi di ingestione pari a 7.86-22.26 µgC L-1 negli esperimenti superficiali e 0.53-10.61 µgC L-1 negli esperimenti profondi. Un’abbondanza picoplanctonica di 108 cellule L-1 è stata ipotizzata come necessaria per sostenere la comunità degli flagellati. Nonostante l’aumento della profondità comporti una riduzione dell’abbondanza del picoplancton tale da non raggiungere questa soglia, i nostri dati confermano che anche negli ambienti profondi si instaurano interazione preda-predatore sufficienti a sostenere le reti trofiche microbiche. Tutte le comunità in situ hanno mostrato la medesima distribuzione, con prevalenza di filotipi rari e pochi gruppi dominanti. Le comunità mesopelagiche presentano diversità e variabilità analoghe a quelle superficiali, nonostante il decremento in biomassa lungo la colonna d’acqua. Una bassa diversità è stata osservata nelle comunità naturali di Archea, dove sono stati rilevati due soli generi (Cenarchaeum e Nitrosopumilus), mentre le comunità batteriche sono composte dai sei principali phyla marini (Proteobacteria, Cyanobacteria, Bacteroidetes, Actinobacteria, Firmicutes e Deinococcus-Thermus), la cui frequenza varia in base alla profondità di campionamento. La predazione esercitata dagli HNF ha modificato la diversità delle comunità sia superficiali che profonde ma con diversi effetti. Le comunità profonde si sono dimostrate più suscettibili alla diversa intensità della predazione. Un controllo top-down medio-alto ha preservato o incrementato la diversità batterica, che invece è risultata fortemente ridotta con bassa pressione di predazione. Al contrario, le comunità superficiali hanno subito solo leggere variazioni nella biodiversità batterica in risposta ai diversi tassi di ingestione, dimostrandosi più stabili. I piccoli flagellati (<3 µm) costituiscono la frazione dominante delle comunità nanoplanctoniche. In seguito alla rimozione dei predatori >3 µm, variazione significative dell’abbondanza sono state riscontrate in una maggiore percentuale di filotipi procariotici. Flagellati di maggiori dimensioni possono quindi mitigare l’impatto dei piccoli predatori sulle prede, con una maggior influenza nei sistemi fotici. Alcuni taxa batterici sono stati consumati prevalentemente dal grandi HNF (3-10 µm), mentre altri sono stati selezionati dai piccoli flagellati (<3 µm). Oltre il 50% dei filotipi predati apparteneva alla biosfera rara, soprattutto negli esperimenti condotti in superficie. I batteri rari (0.1-1% dell’abbondanza totale) non rappresentano quindi una frazione ‘dormiente’ il cui contributo varia in seguito a cambiamenti delle condizioni ambientali, come inizialmente ipotizzato. Costituiscono invece una componente fondamentale delle reti trofiche microbiche e contribuiscono attivamente al trasferimento di carbonio verso i livelli trofici superiori, così come gli organismi dominanti. Nonostante ciascuna comunità risponda in maniera distintiva alla predazione, in funzione della composizione tassonomica delle comunità stesse e dello stato trofico del sistema, alcuni indizi di selettività sono stati individuati. Alcune interazioni preda-predatore si sono rivelate tipiche delle comunità profonde o superficiali, mentre altre erano comuni ad entrambi i sistemi (es. Burkholderiaceae e Pseudomonadaceae sono stati selezionati sono in ambiente pelagico, Bacterivoracaceae sono stati sottoposti a predazione da parte di piccolo flagellati in tutti gli esperimenti, indipendentemente dalla profondità e dal sito di campionamento). I bacini Adriatico meridionale e Ionio settentrionale sono significativamente distinti sia per le caratteristiche chimico-fisiche della colonna d’acqua, sia per l’abbondanza di pico- e nanoplancton. La cluster analisi basata sugli indici di Jaccard e Bray-Curtis ha evidenziato che profondità di campionamento e localizzazione geografica sono i principali fattori che determinano la similarità tra le comunità batteriche. Il Mar Adriatico settentrionale è risultato sempre separato dagli altri campioni, coerentemente con le diverse caratteristiche biotiche e abiotiche del bacino. Oltre a profondità e sito geografico, temperatura, concentrazione di chl a e ossigeno contribuiscono a determinare la biodiversità batterica adriatica e ionica. In conclusione, il presente lavoro ha evidenziato come i flagellati eterotrofi controllino la biomassa procariotica e mostrino preferenza per determinati taxa, selezionando anche quelli rari. La predazione influenza la struttura delle comunità e di conseguenza il funzionamento degli ecosistemi. Anche gli ambienti marini profondi ospitano complesse reti trofiche, strutturate attorno a tre livelli principali (procarioti, piccoli e grandi flagellati eterotrofi) così come le acque superficiali.
XXVI Ciclo
1986

Chromera velia was discovered a decade ago associated with stony corals in the Great Barrier Reef and Sydney Harbour, Australia. This unicellular alveolate possesses housekeeping genes and ultrastructural features typical of apicomplexans, and has active photosynthetic pathways related to dinoflagellates. This unique connection suggests that C. velia can be used to understand the evolution of apicomplexan parasites from their algal ancestors. C. velia exists in either an immotile coccoid state or an active motile flagellated form. The life cycle is not well understood and little is known about what triggers the transformation between states, and how this translates to ecological conditions. With its structural similarity to both apicomplexans and dinoflagellates, the flagellated form of C. velia represents a relatively unexplored part of the life cycle that is critical for understanding the ecological significance of this novel organism. The presence of a flagellated state may enhance competitive fitness of the organism under certain environmental conditions. This thesis investigated the flagellated form of C. velia and explored environmental factors that induce or suppress flagellation. Optimised conditions for flagellation were then used to test the flagellated form as a screening platform to test anti-apicomplexan drugs. In addition, the ecology and biodiversity of C. velia was explored by screening freshly procured coral samples for new chromerid cultures. To explore the flagellated state of C. velia cells were cultured in a range of light, temperature and physical and chemical stress conditions. Light wavelength had a significant effect on flagellation, with different spectra causing the induction or suppression of flagellation. The highest levels of flagellation were seen when C. velia was cultured in blue light or the dark. C. velia exhibited a temporal cycle of motility over 24 hours similar to that of the coral symbiont Symbiodinium, which exhibits motility rhythms in a light-dark environmental cycle. However, in C. velia this pattern continued when the cells were grown in constant dark, suggesting that the cycle is not completely light dependent. High cell density completely suppressed flagellation, and no flagellates were seen in cultures of 106 cells/mL. Non-optimal temperatures and a range of other stressors either killed cells or suppressed flagellation, but did not induce it. A negative correlation was found between light conditions inducing cell multiplication and flagellation, and this has been explored in a proposed new amendment to the life cycle model. Culturing techniques adapted by Moore (2006) were used to screen coral samples for novel chromerids to gain a better understanding of the biodiversity and ecological niche of C. velia. A new strain of C. velia was isolated from L. purpurea present in the Heron Island lagoon, and this additional strain was used in developing a multilocus sequence typing (MLST) system with eight genetic loci that was able to differentiate the three strains of C. velia that are now available. The three strains had considerable diversity at the genetic level, and attempts were made to distinguish them phenotypically by studying growth, flagellation and B vitamin synthesis. The three strains did not require the addition of B vitamins for growth, and possessed a typical algal B7 synthesis pathway, no synthesis or requirement for B12, and an unusual B1 synthesis pathway involving a mosaic of genes with closest homologs of bacterial and fungal origin. New insights on flagellation in C. velia were used to design a flagellation assay to screen compounds for apicomplexan drug development. The Malaria Box, a set of 400 compounds with anti-malarial activity, was provided by the Medicines for Malaria Venture and screened using this assay, finding a number of positive hits. These positive hits were used by structural chemist collaborators at SPECS to synthesise an additional 80 structurally similar compounds that were also screened. A high proportion of compounds found to inhibit flagellation in each assay belong to the diaminopyrimidine class of compounds that are known to affect the folate biosynthesis pathway. A bioinformatic study of C. velia folate synthesis revealed a pathway similar to that of Plasmodium, demonstrating that C. velia has biochemical pathways similar to the parasite and screening may pick up compounds that can be used as starting points for therapeutics. C. velia is closely related, phylogenetically speaking to apicomplexans and the flagellated state is the most structurally similar and also the active form, capable of sensing changes in the environment and moving the cell in response to these changes. To date most studies have only looked at the structure of this form and little has been done to explore its role in the life cycle of C. velia. This study has provided new insights into the ecology and biodiversity of C. velia by identifying triggers for flagellation, producing an amended life cycle model, identifying a new strain of C. velia and designing a set of molecular markers for future population studies. The findings were used to design a flagellation assay able to identify compounds that may be useful starting points for anti-apicomplexan therapeutics.

The propulsion of low Reynolds number swimmers has been widely studied, from the swimming sheet models of Taylor (1951), which were analogous to swimming spermatozoa, to more recent studies by Smith (2010) who coupled the boundary element method and method of regularised Stokeslets to look at cilia and flagella driven flow. While the majority of studies have investigated the propulsion and hydrodynamics of spermatozoa and bacteria, very little has been researched on bi-flagellate green algae. Employing an immersed boundary algorithm and a flexible beat pattern Fauci~(1993) constructed a model of a free-swimming algal cell. However, the two-dimensional representation tended to over-estimate the swimming speed of the cell. Jones~\etal~(1994) developed a three-dimensional model for an idealised bi-flagellate to study the gyrotactic behaviour of bottom-heavy swimmers. However, the un-realistic cell geometry and use of resistive force theory only offered order of magnitude accuracy. In this thesis we, investigate the hydrodynamics of swimming bi-flagellates via the application of the method of regularised Stokeslets, and obtain improved estimates for swimming speed and behaviour. Furthermore, we consider three-dimensional models for bi-flagellate cells with realistic cell geometries and flagellar beats. We investigate the behaviour of force- and torque-free swimmers with bottom-heavy spheroidal bodies and two flagella located at the anterior end of the cell body, which beat in a breast stroke motion. The cells exhibit gravitactic and gyrotactic behaviour, which result in cells swimming upwards on average in an ambient fluid and also towards regions of locally down-welling fluid, respectively. In order to compare how important the intricacies of the flagellar beat are to a cell's swimming dynamics we consider various beat patterns taken from experimental observations of the green alga \Rein~and idealised approaches from the literature. We present models for the bi-flagellate swimmers as mobility problems, which can be solved to obtain estimates for the instantaneous translational and angular velocities of the cell. The mobility problem is formulated by coupling the method of regularised Stokeslets with the conditions that there is no-slip on the surface of the body and flagella of the cell and that there exists a balance between external and fluid forces and torques. The method of regularised Stokeslets is an approach to computing Stokes flow, where the solutions of Stokes equations are desingularised. Furthermore, by modelling the cells as self-propelled spheroids we outline an approach to estimate the mean effective behaviour of cells in shear flows. We first investigate bi-flagellate swimming in a quiescent fluid to obtain estimates for the mean swimming speed of cells, and demonstrate that results for the three-dimensional model are consistent with estimates obtained from experimental observations. Moreover, we explore the various mechanisms that cells may use to re-orientate and conclude that gyrotactic and gravitactic re-orientation is due to a combination of shape and mass asymmetry, with each being equally important and complimentary. Next, we compare the flow fields generated by our simulations with some recent experimental observations of the velocity fields generated by free-swimming \rein, highlighting that simulations capture the same characteristics of the flow found in the experimental work. We also present our own experiments for \rein~and \Dunny~detailing the trajectories and instantaneous swimming speeds for free-swimming cells, and flow fields for trapped cells. Furthermore, we construct flagellar beats based upon experimental observations of \dunny~and \textit{D. bioculata}, which have different body shapes and flagellar beats than \chlamy. We then compare the estimates for swimming speed and re-orientation time with \rein, highlighting that, in general, \Dun~achieve greater swimming speeds, but take longer to re-orientate. The behaviour of cells in a shear flow is also investigated showing that for sufficiently large shear, vorticity dominates and cells simply tumble. Moreover, we obtain estimates for the effective cell eccentricity, which, contrary to previous hypotheses, shows that cells with realistic beat patterns swim as self-propelled spheres rather than self-propelled spheroids. We also present a technique for computing the effective eccentricity that reduces computational time and storage costs, as well as being applicable to unordered image data. Finally, we examine what effects interactions with boundaries, other cells, and obstacles have on a free-swimming cell. Here, we find that there are various factors which affect a cell's swimming speed, orientation and trajectory. The most important aspect is the distance between the interacting objects, but initial orientation and the flagella beat are also important. Free-swimming cells in an unbounded fluid typically behave as force-dipoles in the far field, and we find that for cell-to-cell and cell-to-obstacle interactions the far field behaviour is similar. However, swimming in the proximity of a boundary results in the flow field decaying faster. This implies that hydrodynamic interactions close to solid no-slip surfaces will be weaker than in an infinite fluid.

In der vorliegenden Arbeit wurden 212 Kotproben von Chamäleons auf Parasitenstadien und 75 Tierkörper pathologisch sowie bei einem nachgewiesenen Parasitenbefall histopathologisch untersucht. Ziel war es, anhand dieser Untersuchungen das Vorkommen und die Schadwirkungen von Endoparasiten unter Berücksichtigung der Herkunft, des Alters, des Geschlechts und der Chamäleonart zu beschreiben. Von 212 Kotproben wiesen 55,2% Endoparasitenstadien auf. Bei 54,7% der 64 sezierten und auswertbaren Tiere wurden Endoparasiten nachgewiesen. Der Anteil positiver Proben zeigt zwischen Nachzuchten (55,5%) und Wildfängen (54,1%) keinen wesentlichen Unterschied. In Wildfängen konnten häufiger Endoparasiten mit einem indirekten Lebenszyklus ermittelt werden, Nachzuchten beherbergten dagegen öfter Parasiten mit einem direkten Entwicklungszyklus. In den untersuchten Chamäleons konnten regelmäßig Kokzidien der Gattung Isospora und Oxyuriden nachgewiesen werden. Zestoden konnten in der koproskopischen Untersuchung gar nicht aufgefunden werden, wohingegen sie in der pathologischen Untersuchung sporadisch im Darm diagnostiziert werden konnten. Die Häufigkeit des koproskopischen Nachweises von Parasitenstadien bezogen auf die Gesamtzahl der untersuchten Chamäleons stellte sich wie folgt dar: in 30,4% wurden Protozoon gefunden, 21,7% der Tiere waren mit Kokzidien infiziert (davon 78,3% Isospora spp., 13,0% Choleoeimeria spp., 6,5% Eimeria spp., 2,2% Mischinfektion Isospora spp./Choleoeimeria spp.) und 8,5% mit Flagellaten oder Ziliaten. Bei 83,3% der Tiere mit gastrointestinalen Symptomen konnte ein Befall mit Kokzidien der Gattung Isospora nachgewiesen werden. In 38,7% der koproskopischen Untersuchungen konnten Nematoden (65,9% Oxyuriden, 19,5% Askariden/ Heterakiden, 1,4% Rhabdias sp., 2,8% Strongyloides sp., je 0,5 % Spirurida, Heterakiden/Filarien, Oxyuriden/Strongyloiden) und in 2,8% Trematoden (Digenea) aufgefunden werden. Anamnestisch konnten in 35,8% aller Tiere klinische Symptome beobachtet werden, wovon bei 88,2% der erkrankten Tiere ein Endoparasitenbefall nachzuweisen war. Insgesamt 64,1% der sezierten Chamäleons waren mit Endoparasiten befallen, wovon 68,3% Mono- und 31,7% Mischinfektionen beherbergten. In 31,3% der sezierten Chamäleons wurden Nematoden gefunden und der Befall wurde in 55,0% dieser Fälle als hochgradig eingestuft. Es wurden Befallsraten von 25,0% für Strongyloides sp., 23,4% für Askariden/ Heterakiden,15,0% für Filarien, 5,0% für Rhabdias sp., 9,4% für Zestoden, 10,9% für Digenea registriert. In 11,3% der Fälle lagen Mischinfektionen vor. Damit ist ein Endoparasitenbefall bei Chamäleons häufig und kann zu Erkrankungen führen. Die Exposition unterscheidet sich bei Wildfängen und Nachzuchten aufgrund der unterschiedlichen Umgebungsbedingungen. Auch klinisch unauffällige Tiere waren zu 27,8% mit Parasiten befallen, so dass eine klinische Symptomatik nicht zwingend aus einem Parasitenbefall resultiert. Insgesamt betrachtet verdient der Endoparasitenbefall von Chamäleons das Augenmerk von Tierärzten und Tierhaltern und sollte bei augenscheinlich hohem Infektionsdruck zu Gegenmaßnahmen, insbesondere auch einer verbesserten Hygiene, Anlaß geben
In the present study 212 chameleon fecal samples were examined for parasite stages and 75 carcasses were examined histopathologically and pathologically in a proven case of a parasite infestation. The basis of this study was to describe the occurrence and harmful effects of internal parasites considering the origin, age and sex of the chameleons. Of the 212 fecal samples 55.2% showed stages of endoparasites. Parasites were detected at 54.7% of 64 evaluated and dissected animals. The proportion of positive samples shows no significant difference between offspring (55.5%) and wild specimens (54.1%). In wild specimens common internal parasites could be determined with an indirect life cycle, however offspring harbored more parasites with a direct life cycle. In the studied chameleons coccidia as the genus Isospora and Oxyurids were regularly detected. In the coprological study Cestodes could not be found, while in the pathological examination they could be diagnosed sporadically in the intestine. Based on the total number of investigated chameleons the frequency of detection of parasite stages are presented as follows: Protozoa were found in 30.4%, 21.7% of the animals were infected with coccidia (of which 78,3% Isospora spp, 13,0% Choleoeimeria spp., 6.5% Eimeria spp., 2.2% polyinfections between Isospora spp./ Choleoeimeria spp.) and 8.5% with flagellates or ciliates. At 83.3% of the animals with gastrointestinal symptoms coccidia of the genus Isospora were detected. In 38.7% of the fecal examination nematodes were determined (65.9% Oxyurids, 19.5% Ascarids/ Heterakis, 1.4% Rhabdias sp., 2.8% Strongyloides sp., 0.5% Spirurida, Heterakids/ Filariae, Oxyurids/ Strongyloides sp.) and Trematodes in 2.8% (Digenea) were found. The anamnesis showed that clinical symptoms could be observed in 35.8% of all of the animals, whereas endoparasite infestation could be detected inn 88.2% of the affected animals. Overall, 64.1% of the dissected chameleons were infested with parasites, of which 68.3% harbored mono- and 31.7% polyinfections. In 31.3% of the dissected chameleons nematode infestations were found and 55.0% of these cases were classified as severe. Prevalences were registered: 25.0% for Strongyloides spp., 23.4% for Ascarids/ Heterakids, 15.0% for Filaria, 5.0% for Rhabdias sp., 9.4% for Cestodes, 10.9% for Digenea. In 11.3% of the cases mixed infections were reported. Thus, endoparasite infestation is common among chameleons and can lead to diseases. Exposure differs from wild-specimens and captive-bred due to the different environmental conditions. Also, 27.8% of clinically healthy animals were also infested with parasites, which means that clinical symptoms are not necessarily the result of a parasitic infestation. Overall, chameleon endoparasites deserve the attention of veterinarians and pet owners and should be treated promptly when there is a high likelihood of infection or hygiene is of concern

Bacterial flagellar filaments are long cell surface appendages that generate propulsion for movement. They also play key roles in surface attachment and host-bacterial interactions. The filament is made from a single protein species flagellin. Approximately 45 % of annotated flagellar systems possess multiple flagellin genes. We have investigated the ability of Caulobacter crescentus to build a flagellar filament using six flagellins: FljJ, FljK, FljL, FljM, FljN and FljO. Our analysis showed that this flagellar system exhibits extensive structural redundancy, in that one species of flagellin is sufficient to sustain motility. However, when that flagellin is FljJ cells are non motile. Distinct flagellar assembly checkpoints are utilised by bacteria in order to coordinate and couple flagellar gene expression to the assembly pathway. One of these checkpoints, hook-basal-body completion, is sensed and overcome by the secretion of a flagellar-associated secretion substrate. This mechanism results in a system switch to the export of proteins, which are needed for filament assembly. In C. crescentus the post-transcriptional regulators FlbT and FlaF have been implicated to function at this switch. As the flagellins themselves are being secreted we asked the logical question: are the flagellins involved in subunit feedback control of the regulation of filament assembly? In a bacterial two-hybrid assay, FljJ was the only flagellin able to interact with FlbT and FlaF. Furthermore, FljJ along with FlbT was found to interact with flagellin mRNA. In light of our data we a propose model for the regulation of flagellar filament assembly in C. crescentus and discuss the implications with respect to other flagellar systems

This project investigated the Potential for using the bacterial flagellar filament as a functionalized protein nanotube. A varied approach to flagellin engineering was taken using the flagella of E. coli and R. sphaeroides, with engineered flagellar flilaments from E. coli proving successful. A variety ofepitopes were inserted into the E. coli flagellin, resulting in filaments which displayed adhesive peptides or cleaveable sites. His-tagged filaments allowed the binding of metal ions and nanoparticles, and the biotin-avidin system was empl~yed to allow more specific binding of ligands. Cys-tagged filaments were 'made to order' for a collaborator to allow improved binding of gold to flagellar filaments. The TEV protease recognition site was used to allow specific cleavage of the surface displayed portion of the flagellin within the intact filament structure. Other proteases allowed further digestion ofthis surface displayed region. By combining the adhesive epitope with flanking TEV protease sites selective excision of the tag was possible, allowing the potential for directed whole filament removal from a surface or scaffold in applications such as nanolithography. An in trans expression system was developed to allow assembly of different flagellins into the same filament, with expression levels varied to result in specific ratios of each functionalised monomer. This allowed the creation of bi-functional protein nanotubes, which could bind more than one ligand.

Flagellin was demonstrated to initiate signalling responses in intestinal epithelial cells resulting in the induction of interleukin-8 (IL-8) and human beta defensin-2 (hBD-2) genes.  Intestinal epithelial cell responses to flagellin isolated from both these organisms and signalling responses to whole bacteria and their mutants was examined. Studies with S. enteritidis mutants confirmed the importance of flagellin in signalling responses in Caco-2 intestinal epithelial cells.  Flagellin was a requirement for the nuclear locations of the transcription factor NF-κB.  IL-8 and hBD-2 gene transcription in response to S. enteritidis was found to be dependent on bacterial cell density.  At high densities there was a down-regulation in the induction of these genes.  This down-regulatory signal was isolated in bacterial cell-free conditioned media.  Experiments with R. intestinalis in a novel anaerobic/aerobic co-culture system also suggested that this organism may regulate aspects of the intestinal epithelial cell response to flagellin.  Proteomic methods were employed to characterise proteins in bacterial cell-free conditioned media produced by S. enteritidis, and also to examine density-dependent changes in the S. enteritidis proteome.  These techniques were also employed to investigate epithelial cell-induced changes in the proteome of flagellate commensal Roseburia hominis. In summary this study confirmed previous published evidence that flagellin is important in signalling responses in Caco-2 cells challenged with S. enteritidis. Novel experiments with commensal R. intestinalis derived flagellin (fliC gene sequenced in this project) showed that it also induced the transcription of IL-8 and hBD-2 genes.

Flagella and cilia are thin, active organelles protruding from cells that are used to propel the cell or move fluid. The flagellated alga Chlamydomonas reinhardtii is a uni-cellular model organism well-suited for the study of flagellar and cilia mechanics.

Bacterial flagella have been employed as nanoactuators for biomimetic microswimmers in low Reynolds number fluidic environments. The microswimmer is a dumbbell-like swimmer that utilizes flagellar hydrodynamics to achieve spiral-type swimming. Flagellar filaments from Salmonella typhimurium are harnessed and functionalized in order to serve as couplers for polystyrene (PS) microbeads and magnetic nanoparticles (MNPs) using avidin-biotin chemistry. The MNP have an iron oxide core that will allow us to actuate the microswimmer under a rotating magnetic field. Using a micromanufacturing process, microswimmer of different configurations can be created to mimic mono- and multi-flagellated bacteria. A magnetic control system consists of electromagnetic coils arranged in an approximate Helmholtz configuration was designed, constructed, and characterized. In conjunction with a LabVIEW input interface, a DAQ controller was used as a function generator to generate sinusoidal waveforms to the power supplies. AC current outputs were supplied from the power supplies to the coils in order to generate a rotating magnetic field. A rotating magnetic field will induce rotation in the flagella conjugated MNP which in term will rotate the flagellar filament into a spiral configuration and achieve propulsion, as in polarly-flagellated bacteria. A high-speed camera provided real-time imaging of the microswimmer motion in a static fluidic environment inside a closed PDMS (Polydimethylsiloxane) chamber. The microswimmers exhibited flagellar propulsion in a low Reynolds number fluidic environment under a rotating magnetic field, which demonstrates its potential for biomedical applications.

Drug delivery systems have had a profound impact on several branches of medicine. Engineers and researchers alike have labored to create a controlled drug delivery device capable of regulated dosage release and a specific cell targeting mechanism. The growing field of biomimicry has inspired several of these drug systems, though success has been limited. The flagellated low Reynolds number propulsion system of Salmonella typhimurium has inspired this specific delivery complex. In this system, the helical flagellar filaments of S. typhimurium are isolated from the bacteria’s cell body and are bound to functionalized paramagnetic microspheres. As a magnetic field is applied to this device, the microsphere rotates, inducing rotation of the helical flagella. This motion creates a locomotive force and drives the device in a predestined direction.

At the microscale, the ability to precisely move objects on the scale of microns is a challenge. One method is to use microbiorobots (MBRs), constructed of a neutrally-buoyant microstructure powered by a monolayer of swarmer flagellated bacteria adhered to the surface. The bacteria swim to propel the microstructure in a fluidic environment in the absence of external forces. The trajectory is a combination of translation and rotation, with the rotation generally observed to be clockwise when viewed from above. In order to create a dynamic model of the inherent motion of MBRs, we use UV light to immobilize the bacteria on different regions of an MBR and characterize the resultant motion. We show that the bacteria on the edge of the structure have different force contributions than those in the center of the microstructure where the flagella cannot interact with the surface under that MBR. This is a step towards improved accuracy in the control of MBRs when external forces are applied for manipulation.

To achieve a high degree of functional density and efficiency, some of the micro actuators in MEMS can be replaced by active biological elements. An example of this is the cellular motor micro pump (CMMP) currently under development at the University of Arkansas. The CMMP is realized through the tethering of a harmless strain of Escherichia coli cells to a MEMS-based micro fluidic channel. In a free moving state, an E.coli cell ‘swims’ by rotating its’ flagella, driven at the base by a rotary motor. When a cell is attached to a surface by a single shortened flagellar filament (∼0.5 micron long), the motor turns the entire cell body at a high rotational speed. The CMMP utilizes this mechanism to transport liquid in a micro fluidic channel through viscous pumping. This paper describes two important areas in the CMMP development process: cell tethering in micro channels fabricated from various substrate materials and visualization of tethered cell behavior through fluorescent microscopy.

One of the primary goals of medical micro and nano robots is to reach currently inaccessible areas of the human body and carry out a host of complex operations, such as minimally invasive surgery (MIS), highly localized drug delivery, and screening for diseases at their very early stages. One of the innovative approaches to design microrobot propulsion is based on the flagellar motion of bacteria [1]. Certain bacteria, such as Escherichia coli (E.coli) use multiple flagella often concentrated at one end of their bodies to induce locomotion. Each flagellum is formed in a left-handed helix and has a motor at the base that rotates the flagellum in a corkscrew motion. As pointed out by Purcell in his Lecture “Life at low Reynolds numbers” [2], microorganisms experience an environment quite different from our own. In particular, because of their small size (of the order of microns), inertia is, to them, essentially irrelevant. The fact that inertia is irrelevant for micro-organisms makes it difficult for them to move. The propulsive mechanisms based on flow inertia will not work on a mesoscopic scale. To overcome this problem, organisms living in low Reynolds number regimes have developed moving organelles which have a handedness to them. For instance, E. Coli’s flagella rotate with a helical motion, much like a corkscrew. This configuration produces patterns of motion that do not repeat the first half of the cycle in reverse for the second half, allowing the organisms to achieve movement in their environment.

A novel method for detecting and configuring bacteria using a micro-scale pore is presented. The method distinguishes between different species of bacteria by measuring the ionic current blockage (resistive pulse) as bacteria electrophoretically translocate the micro-pore. Both wild-type flagellated (HCB 33) and non-flagellated Escherichia coli (HCB 5), and Polystyrene microbeads were used in this study to demonstrate the efficacy of this method. High resolution electrical signal readout enabled discrimination of the orientation of both non-flagellated and peritrichously flagellated bacteria as they move through the solid-state pore.

Microfluidic actuators are extremely important components of microfluidic systems used in biological, chemical and biochemical analyses. We are in the process of developing hybrid microsystem devices that utilize flagellar motors in tethered Escherichia coli (E.coli) cells as actuators. In this study we describe the robustness of the flagellar motor actuators. To examine the robustness of the actuators we observe the behavior of the cells when exposed to a hydrodynamic load. With this method we are able to determine the torque generated by the flagellar motor and the adhesion force of the flagellar filament to the substrate. Using hydrodynamic loading we are also able to synchronize the rotation of multiple cells. Finally, we present data which represents the lifetime of the flagellar motor actuators.