Literatura académica sobre el tema "Population de Streptomyces"

Population dynamics of Streptomyces spp. producing melanoid pigments were monitored in field plots planted to the potato cultivars 'Chippewa' (susceptible to common scab) or 'Superior' (resistant), and in fallow control plots. Relative frequencies of streptomycetes most commonly isolated from soil, the rhizosphere, and potato tuber surfaces were determined during two growing seasons. Shannon indices of diversity indicated populations in soils planted to potatoes were more diverse than populations in fallow soil. In 1986, S. diastatochromogenes and S. longisporus accounted for ≥38% of all streptomycetes observed in all three environments. In 1987, S. diastatochromogenes was observed frequently in soil, while S. longisporus was observed rarely in all environments. Relative numbers of three Streptomyces spp. differed in the rhizospheres of 'Chippewa' and 'Superior' (P ≤ 0.05). This is the first report of a differential response of Streptomyces spp. to potato cultivars. Key words: rhizosphere, Solanum tuberosum, Streptomyces spp., melanin.

Nonpathogenic, antibiotic-producing streptomycetes have been shown to reduce potato scab when added to disease-conducive soil. Spontaneous mutants of the pathogenic Streptomyces scabies RB4 that are resistant to at least one antibiotic activity produced by the nonpathogenic suppressive isolates Streptomyces diastatochromogenes strain PonSSII and S. scabies PonR have been isolated. To determine the importance of antibiosis in this biocontrol system, these mutants were investigated for their ability to cause disease in the presence of the two pathogen antagonists in a greenhouse assay. Disease caused by one of the mutant strains was reduced in the presence of both suppressive isolates, whereas disease caused by the other five mutants was not significantly reduced by either suppressive strain. In addition, a nonpathogenic mutant of S. scabies RB4 was isolated, which produced no detectable in vitro antibiotic activity and reduced disease caused by its pathogenic parent strain when the pathogen and mutant were coinoculated into soil. Population densities of the pathogen were consistently lower than those of the suppressive strains when individual strains were inoculated into soil. When a pathogen was coinoculated with a suppressive strain, the total streptomycete population density in the pot was always less than that observed when the suppressive isolate was inoculated alone. When the pathogens were inoculated individually into soil, a positive correlation was seen between population density and disease severity. In coinoculation experiments with pathogen and suppressive strains, higher total streptomycete population densities were correlated with lower amounts of disease.Key words: Streptomyces scabies, biological control, antibiotic resistance, potato scab disease.

A field in East Lansing, MI, showed a decline of potato common scab compared with an adjacent potato field. To confirm that the decline was due to biological factors, the soil was assayed. In the greenhouse, putative common-scab-suppressive soil (SS) was either treated with various temperatures or mixed with autoclaved SS at various ratios. Pathogenic Streptomyces scabies was incorporated into the treated soil at 106 CFU/cm3 of soil, followed by planting of either potato or radish. Disease severity was negatively correlated with the percentage of SS in the mixture and positively correlated with temperature above 60°C. The soil was screened for four groups of potential antagonists (general bacteria, streptomycetes, fluorescent pseudomonads, and bacilli) pairing in culture with S. scabies. The frequency of antagonistic bacteria in SS was higher than common-scab-conducive soil (CS) in all four groups but only pseudomonads and streptomycetes were significantly higher. The population of pathogenic Streptomyces spp. in the rhizosphere of CS was significantly higher than SS. Dilution plating of CS and SS samples showed no clear trends or differences in populations of total fungi, total bacteria, streptomycetes, fluorescent pseudomonads, and bacilli but terminal restriction fragment polymorphism analysis revealed two distinct microbial communities were present in SS and CS.

Analysis of cellular fatty acid profiles was used to distinguish among introduced pathogen- suppressive strains and indigenous strains of Streptomyces spp. isolated from soil of field plots established to test the efficacy of Streptomyces strains PonSSII and PonR in the biological control of potato scab. Reference libraries of fatty acid profiles were developed for a collection of known pathogenic strains and the introduced suppressive strains. Population densities of pathogen-related, suppressive, and saprophytic Streptomyces strains were determined from the relationship of field isolates to mean library profiles using cluster analysis and the unweighted pair-group method using arithmetic averages. Community diversity was similarly determined. Streptomyces strains PonSSII and PonR were distinguished from each other and from the pathogen group (which clustered together) based on fatty acid profiles. The introduced, suppressive strains successfully colonized the soil and represented 2–19% of the isolates sampled over 2 years. The introduction of the suppressive strains inhibited the population of strains related to the pathogen library at each sample date; the pathogen population was substantially lower in soil from treatments where the suppressive strains were introduced compared with the nonamended control. At harvest, the pathogen-related population was suppressed 85–93 and 36–44% in 1991 and 1992, respectively, in treatments with the suppressive strains compared with the nonamended control. Diversity of the community was not affected by the introduced strains, and diversity and equitability indices were similar among treatments at any sample time. The inhibition of the pathogen-related population was correlated with a reduction of scab symptoms observed in the field plots into which the suppressive strains were introduced. Implications of a fundamental shift in the pathogen-related population in response to the introduction of the suppressive strains for long-term biological control of potato scab are encouraging.Key words: Streptomyces, fatty acid analysis, biological control, community ecology.

Bacteria of the genus Streptomyces, one of the main microorganisms of soils, and their bacteriophages are important inhabitants of soil ecosystems. Important though they are, not much is known about their functional patterns and population dynamics. A question of particular interest, which is still to be understood, is how bacteriophages regulate the population dynamics of Streptomyces and how this regulation affects the soil ecosystem as a whole. Isolation and study of new Streptomyces bacteriophages can help to understand these problems. In this paper, we describe isolation of a new bacteriophage from the soils of the Prioksko- Terrasny Reserve. The analysis of morphology of the new phage allows us to conclude that it belongs to the family Siphoviridae.

ABSTRACTExamining the population structure and the influence of recombination and ecology on microbial populations makes great sense for understanding microbial evolution and speciation. Streptomycetes are a diverse group of bacteria that are widely distributed in nature and a rich source of useful bioactive compounds; however, they are rarely subjected to population genetic investigations. In this study, we applied a five-gene-based multilocus sequence analysis (MLSA) scheme to 41 strains ofStreptomyces albidoflavusderived from diverse sources, mainly insects, sea, and soil. Frequent recombination was detected inS. albidoflavus, supported by multiple lines of evidence from the pairwise homoplasy index (Φw) test, phylogenetic discordance, the Shimodaira-Hasegawa (SH) test, and network analysis, underpinning the predominance of homologous recombination withinStreptomycesspecies. A strong habitat signal was also observed in both phylogenetic and Structure 2.3.3 analyses, indicating the importance of ecological difference in shaping the population structure. Moreover, all three habitat-associated groups, particularly the entomic group, demonstrated significantly reduced levels of gene flow with one another, generally revealing habitat barriers to recombination. Therefore, a combined effect of homologous recombination and ecology is inferred forS. albidoflavus, where dynamic evolution is at least partly balanced by the extent that differential distributions of strains among habitats limit genetic exchange. Our study stresses the significance of ecology in microbial speciation and reveals the coexistence of homologous recombination and ecological divergence in the evolution of streptomycetes.

The influence of Ilkompost and Micromix bacterial consortium inoculation during sewage sludge (SS) with wheat straw (WS) composting was assessed. The effect of inoculation on compost quality parameters such as pH, temperature, nutrient contents and C/N, bacterial and fungal population were determined. Compared to the control treatment, the temperature of piles and population of microorganism increased after inoculated bacterial consortiums at the beginning of compost. But, WS addition did not effect on compost quality parameters and microbial population. Fungal and bacterial population, the peak temperature, or heating rate, of Micromix bacterial consortium based on Streptomyces pratensis, Bacillus mesentericus, Azotobacter chroococcum inoculated treatments was clearly higher than that of Ilkompost bacterial consortium based on Pediococcus pentosaceus, Streptomyces sindenensis, Bacillus megaterium inoculated treatments

Streptomyces albus J1074 has recently emerged as a powerful chassis strain for natural product research and discovery, as well as model to investigate various aspects of actinobacterial biology. A number of genetic tools have been developed to facilitate the use of this strain for the aforementioned purposes. One of the promising approaches is to introduce into J1074 genome mutations that would improve the antibiotic-producing capacity of J1074. Particularly, we reported a collection of spontaneous and genomically engineered J1074 mutants carrying mutation in genes for ribosomal protein S12, RNA polymerase beta subunit etc. We took advantage of this collection to build an in-house database which would host (both current and future) the primary and curated sequencing data for these mutants. The database is available at https://biotools.online/media/. The main benefits of the database lie in the known pedigree of the strains, which allows deep interpretation of the data. For example, there is lively – and unresolved – debate on the origins and consequences of the GC composition in actinobacteria. A better understanding of this issue should improve our knowledge of genome evolution in bacteria and will have a number of biotechnological ramifications. We used our Streptomyces albus J1074 dataset as an experimental model to reveal genome-wide spectrum of mutation, which appears to be biased towards elevated GC content. We also included the high-quality genomes of the other streptomycetes into our databse for comparative purposes. The genomic GC content in streptomycetes varies from 75 % to 66.5 %, with median value being 72 %. The GC content of secondary metabolic genes of S. coelicolor is less variable than that of primary metabolic genes, an indicative of different selection pressure on these gene groups. Along with selective constraints, the peculiarities of Streptomyces DNA mismatch repair might contribute to the skewed GC content of their genomes. Further uses of the database may include the development of a more precise knowledge of the mutation rate as well as population genetic processes within this species and genus.

A procedure is described for estimating Streptomyces populations in soil. Soils are air-dried, 10g quantities are shaken in plastic bags containing 0.1% water agar and homogenized with a Stomacher homogenizer, serial dilutions are plated on a semi-selective culture (STR) medium and incubated for 2 weeks at 22°C, and the Streptomyces colonies are enumerated. Use of STR medium reduced the bacterial and fungal colonies recovered from soil to levels below that of the Streptomyces spp. while not affecting the number of Streptomyces colonies compared with those enumerated on yeast malt extract medium. A procedure for screening large numbers of Streptomyces strains for thaxtomin production, a phytotoxin recognized as a virulence marker in S. scabies, is also described. Strains are grown on oatmeal medium, and the thaxtomin is extracted from the medium by facilitated diffusion and detected by miniature thin layer chromatography. S. scabies and S. acidiscabies strains (approximately 130 from Ontario and 70 from other locations in North America) that produced thaxtomin did not form aerial mycelia or sporulate on STR medium within 2 weeks at 22°C. Ontario S. scabies strains that produced thaxtomin A also produced melanin on STR medium. All S. scabies strains from scab lesions that produced thaxtomin A had this colony morphology, whereas only 4 to 9% of strains from soil with this colony morphology produced thaxtomin A. Using these procedures, we determined that the population of thaxtomin-producing S. scabies in soil from a potato field in Ontario with a history of potato scab was about 20,000 CFU/g soil.

Potato common scab (PCS), caused by pathogenic Streptomyces spp., is a serious disease in potato production worldwide. Cultural practices, such as optimizing the soil pH and irrigation, are recommended but it is often difficult to establish stable disease reductions using these methods. Traditionally, local farmers in southwest Japan have amended soils with rice bran (RB) to suppress PCS. However, the scientific mechanism underlying disease suppression by RB has not been elucidated. The present study showed that RB amendment reduced PCS by repressing the pathogenic Streptomyces population in young tubers. Amplicon sequencing analyses of 16S ribosomal RNA genes from the rhizosphere microbiome revealed that RB amendment dramatically changed bacterial composition and led to an increase in the relative abundance of gram-positive bacteria such as Streptomyces spp., and this was negatively correlated with PCS disease severity. Most actinomycete isolates derived from the RB-amended soil showed antagonistic activity against pathogenic Streptomyces scabiei and S. turgidiscabies on R2A medium. Some of the Streptomyces isolates suppressed PCS when they were inoculated onto potato plants in a field experiment. These results suggest that RB amendment increases the levels of antagonistic bacteria against PCS pathogens in the potato rhizosphere.

Les Streptomyces sont des bactéries de la rhizosphère qui contribuent à la fertilité des sols (recyclage de la matière organique), et à la croissance et la santé des plantes. Elles possèdent parmi les plus grands génomes bactériens (12 Mb) et présentent une variabilité génétique importante. Cette variabilité connue au niveau interspécifique n’a jamais été abordée à l’échelle de la population, c’est-à-dire entre individus sympatriques appartenant à la même espèce (souches sœurs) au sein de la même niche écologique. L’objectif de ce travail est de rechercher cette diversité dans les populations de l’écosystème sol forestier, d’approcher sa dynamique et son rôle fonctionnel. Après séquençage et comparaison des génomes complets, nous avons observé une grande diversité génomique en termes de taille, de présence/absence d’éléments extrachromosomiques, mais également en terme de présence/absence de gènes le long du chromosome. Un grand nombre d’événements d’insertions et délétions (indels) comprenant de 1 à 241 gènes différencient les individus de la population. Au vu des liens phylogénétiques étroits entre les individus, l’ancêtre commun de la population est récent, aussi la diversité génomique résulterait d’un flux massif et rapide de gènes. La forte prévalence d’éléments conjugatifs intégrés dans la population suggère que la conjugaison est le moteur prépondérant de cette diversité génomique. La production différentielle de métabolites spécialisés (antibiotiques) a également été utilisée pour estimer l’impact de la diversité génétique sur le fonctionnement de la population. Nous avons pu montrer que cette production était liée à des gènes spécifiques de souches et qu’elle pouvait constituer un bien commun pour la population. Nous proposons que l’évolution rapide du génome participe au maintien des mécanismes de cohésion sociale chez ces bactéries du sol<br>Streptomyces are rhizospheric bacteria that contribute to soil fertility (recycling of organic matter), plant growth and health. They have among the largest bacterial genomes (12 Mb) with a high genetic variability. The genome variability, observed at the interspecific level has never been addressed within a population, i.e. between sympatric individuals belonging to the same species (Conspecific strains) within the same ecological niche. The objective of this work was to investigate this diversity in the forest soil ecosystem, to estimate its dynamics and its potential functional roles. After sequencing and comparison of the complete genomes, we observed a wide genomic diversity in terms of size, presence/absence of extrachromosomal elements, but also in terms of presence/absence of genes along the chromosome. A large number of insertion and deletion events (indels) from 1 to 241 genes differentiate individuals in the population. Given the close phylogenetic relationship of these strains, the common ancestor of the population is recent, hence the genomic diversity would result from a massive and rapid gene flux. The high prevalence of integrative and conjugative elements in the population suggests that conjugation could act as a driving force of this diversity. Differential production of specialized metabolites (antibiotics) was also used to estimate the impact of genetic diversity on population’s ecology. We were able to show that this production was linked to strain specific genes and that it may constitute a « public good » for the population. We propose that the rapid evolution of the genome contributes to the maintenance of social cohesion mechanisms within these soil bacteria

Les Streptomyces sont des bactéries ubiquistes des sols où elles interagissent avec les organismes environnants via un large répertoire de métabolites spécialisés. En étudiant une population rhizosphérique de Streptomyces (des souches de même espèce et isolées du même micro-habitat rhizosphérique), il a été montré que les flux de gènes massifs promeuvent une évolution rapide des individus, permettant leur diversification génétique et fonctionnelle dans le sol forestier. L'objectif de la recherche est de déterminer l'ampleur de ces flux de gènes au sein de la population et les mécanismes responsables des transferts. Les éléments conjugatifs, intégrés (ICE) ou plasmidiques, assurent leur propre transfert et stimulent celui d'ADN chromosomiques. Dans un premier temps, nous avons dressé l'inventaire des ICE spécifiques aux Actinomycetes (AICE) et caractérisé leur richesse, diversité et distribution au sein de la population. Nous avons montré que lors d'un événement de conjugaison unique, plusieurs éléments étaient mobilisés simultanément, et qu'une forte hétérogénéité des AICE était décelable dans la descendance. Afin de mesurer l'ampleur des transferts chromosomiques, nous avons réalisé des croisements entre isolats de la population, puis analysé la séquence du génome des recombinants. Au moyen du polymorphisme nucléotidique, nous avons pu identifier l'origine parentale de chaque segment du génome, et déterminer que la quantité d'information génétique acquise varie entre 1,5 et 35% de l'information totale répartie en plusieurs fragments distincts. Les transferts conjugatifs modifient profondément l'arsenal de gènes codant le métabolisme spécialisé (ex. antibiotiques). En effet, plus de 90% des recombinants se distinguent de leurs parents par les gènes de biosynthèse : gains, pertes, remplacements et recombinaisons. Nous montrons que plusieurs voies de biosynthèse entières (ca. 100 kb) peuvent être acquises par conjugaison. Ainsi, les transferts conjugatifs chez les Streptomyces permettraient de générer une forte diversité intra-populationnelle, diversité nécessaire pour faire émerger des individus plus adaptés, mais aussi pour assurer le partage des tâches au sein de la population dans leur environnement compétitif (sol). Ces résultats ouvrent également des perspectives biotechnologiques avec la possibilité de transferts et de diversification de voies de biosynthèse d'intérêts<br>Streptomyces are ubiquitous bacteria in soils where they interact with surrounding organisms via a wide repertoire of specialized metabolites. By studying a rhizospheric population of Streptomyces, (strains of the same species and isolated from the same rhizospheric micro-habitat), it was shown that massive gene flows promote a rapid evolution of individuals, allowing their genetic and functional diversification in the forest soil. The objective of the research is to determine the magnitude of these gene flows within the population and the mechanisms responsible for the transfers. The conjugative elements, integrated (ICE) or plasmid, ensure their transfer and stimulate that of chromosomal DNA. First, we drew up an inventory of Actinomycetes-specific ICE (AICE) and characterized their richness, diversity, and distribution within the population. We showed that during a single conjugation event, several elements were mobilized simultaneously and that a strong heterogeneity of AICE was detectable in the progeny. To assess the extent of the chromosomal transfers, we performed crosses between isolates of the population and then analyzed the genome sequence of the recombinants. Using nucleotide polymorphism, we were able to identify the parental origin of each segment of the genome and determine that the amount of genetic information acquired varies between 1.5 and 35% of the total information splitted into several distinct fragments. Conjugative transfers profoundly modify the arsenal of genes encoding specialized metabolism (e.g., antibiotics). Indeed, more than 90% of recombinants are distinct from their parents by biosynthesis genes: gains, losses, replacements, and recombination. We show that several whole biosynthetic pathways (ca., 100 kb) can be acquired by conjugation. Thus, conjugative transfers in Streptomyces generate a strong intra-population diversity in a few generations, diversity necessary to raise more adapted individuals, but also to ensure the division of tasks among the population in their competitive environment (soil). These results also open biotechnological perspectives with the possibility of transfers and diversification of biosynthesis pathways of interest

Obligate micro-parasites must enter and compromise a living host cell in order to reproduce. Distinct from symbiosis and commensalism, parasitism results in host mortality or morbidity; the severity of which may be expressed in terms of virulence. Bacteriophage and viruses are ubiquitous in the environment, and localised co-existence of host with parasite is a priori evidence for mechanisms which act to mitigate virulence. When physical separation of host-parasite is not possible, molecular immunity to infection may be selected. The phage growth limitation (Pgl) system of soil bacterium Streptomyces coelicolor confers resistance to temperate phage ΦC31 and clear plaque (virulent) derivatives. A key component of the Pgl mechanism (pglX) is a putative methyltransferase, which resembles a type I restriction modification protein. Phase variable regulation represents an elegant mechanism for generating bi-directional genetic polymorphism; reversible phenotypic diversity. At ca. 10-3 – 10-4 DNA replications, translational phase variation of pglX results from slipped strand mispairing within a polyG-tract. Potential costs associated with the phage-resistant allele were considered. It was hypothesised that the Pgl phenotypes would be distinct in the absence of ΦC31. Growth differences were observed between phase variant S. coelicolor populations in the absence of ΦC31, indicative of Pgl-derived pleiotropy. Liquid infection studies were executed using virulent phage ΦC31cΔ25, designed to exert various degrees of selective pressure on independent cultures of each host phase variant. Under conditions designed to maximise phage-host encounter, the population and evolutionary dynamics of phage and host were interrogated. It was hypothesised that selection for the Pgl-positive allele would be rapid when host seeds were predominantly Pgl-negative. Shaken liquid microcosms were seeded with host, and exposed to ΦC31cΔ25 at various densities (MOI 10, 0.1, 0.001 and 0). Surviving host were purified of exogenous phage, processed, and progeny spores used to inoculate fresh microcosms. Phage selection was maintained at each respective MOI using ancestral (stock) ΦC31cΔ25. Phage adaptation was predictably constrained, however it was hypothesised that pglX phase variation would prevent ancestral ΦC31cΔ25 extinction at an intermediate MOI. At selected microcosm cycles, host populations were screened for phenotypic resistance to ΦC31cΔ25, and a novel adaptation of dHPLC (Transgenomic Inc) was used to resolve and make semi-quantitative the N+/-1 sized pglX alleles within a mixed PCR product. Using host total community DNA, the contribution of Pgl to supporting free ΦC31cΔ25 in addition to host phage-resistance was ascertained. ΦC31cΔ25 mutants bearing lysogenic characteristics emerged during the first infection cycle; a phenomenon reproduced in soil microcosms. While temperance often gives rise to lytic phage mutants in vitro, the converse was most unexpected, particularly during experimental regimes designed to direct evolution in favour of the host. Mutant ΦC31cΔ25 microcosm isolates produced turbid plaques when assayed using S. lividans TK24, and subsequent S. lividans lysogenic spores were superimmune to infection when screened on ΦC31cΔ25-impregnated agar.

Les Streptomyces possédent un large arsenal enzymatique ayant des rôles importants dans le sol. Au cours de cette thèse, nous avons exploré leur diversité génétique, fonctionnelle et écologique à partir de collections provenant de sols forestiers. Ainsi, l’exploration du potentiel cellulolytique et la capacité à détecter des sucres libérés lors de l’attaque du bois par des champignons lignivores a permis de créer un biosenseur dont l’exploitation pourrait constituer un nouvel outil normatif pour la détection de la dégradation du bois. Suite à une approche de génomique comparative réalisée entre des isolats sympatriques, nos résultats ont permis de démontrer que des souches phylogénétiquement très apparentées présentaient de grandes différences en termes de présence/absence de gènes, suggérant une vitesse d’évolution rapide du génome accessoire au sein de la population. Ces gènes, souvent associés à des éléments potentiellement transférables, a souligné un rôle important du transfert horizontal pour la diversification de la population. Par une approche d’écologie réverse, la fonction prédite de certains de ces gènes a également pu être corrélée avec un rôle écologique potentiel. Ainsi, l’un des clusters de gènes variables identifié était impliqué dans la production de métabolites secondaires et pourrait constituer un bien commun pour la population. Nos résultats ont confirmé la grande diversité métabolique des Streptomyces (et leur utilité à des fins appliquées), mais indique également qu’une diversification rapide entre souches proches, aurait un rôle écologique important au niveau des populations naturelles de Streptomyces<br>Streptomyces are known to possess a large enzymatic arsenal which can have important roles in the soil. During this thesis, we explored their genetic, functional and ecological diversity using collections from forest soils. Thus, the exploration of their cellulolytic potential and their ability to detect complex sugars released by wood during lignivorous fungi attacks has led to the creation of a biosensor whose exploitation could constitute a new normative tool for the detection of the degradation of wood. Subsequent to comparative genomic approach carried out between sympatric isolates, our results also demonstrated that phylogenetically highly related strains exhibited large differences in the presence / absence of genes, suggesting a rapid rate of evolution of the population accessory genome. These genes, often associated with potentially transferable elements, underlined important role of horizontal transfer for population diversification. Using a reverse ecology approach, the predicted function of some of these genes could also be correlated with a potential ecological role. Thus, one of the variable gene clusters identified by genome analysis was involved in the production of secondary metabolites and would constitute a common good for the population. All of our results confirm the wide metabolic diversity of Streptomyces (and their utility for applied purposes), but also indicates that this diversification would be rapid between nearby strains and would have an important ecological role in the natural populations of Streptomyces

Surface mucus of a freshwater fish, Alburnus alburnus (bleak), caught from Lake Mogan, situated in south of Ankara, was collected in different seasons. The total cultivable bacteria were enumerated by spread plate method on nine different media. Bacteria were isolated based on colony morphologies and pigmentation. A total of sixty bacterial isolates obtained. The mucus-dwelling bacteria were first tested for resistance against ampicillin and kanamycin<br>then streptomycin and chloramphenicol were added to the experimental set up. The resistance levels of isolates were determined in terms of four antibiotics by tube dilution method. About 90% of the isolates were resistant to chloramphenicol, about 84% to kanamycin, about 88% to streptomycin and about 98% to ampicillin. These high levels of antibiotic resistance are rather interesting from a standpoint that the lake has no record of antibiotics exposure of any sort. The plasmid isolations were carried out to determine if the multiple antibiotic resistance could be attributed to plasmids for starting assumption. But we found no direct relationship between the presence of plasmids and multiple antibiotic resistance. Our study indicated that multiple antibiotic resistance at high levels is among the current phenotypes of the fish mucus-dwelling bacterial populations in Lake Mogan.

碩士<br>國立中興大學<br>植物病理學系所<br>99<br>Numerous microorganisms have the potential to control disease and to promote plant growth, and most of them are considered rhizosphere microorganisms. Co- inoculation of more than one beneficial microorganisms was attempted in previous studies, tried to induce synergistic interaction and increase promotional ability of plant growth or control more diseases. In this study, Streptomyces saraceticus 31 (SS31) was co- inoculated with Bacillus subtilis, Trichoderma sp., phosphate solubilizing bacteria (PSB), nitrogen fixing bacteria (NFB), and mycorrhizal fungi, respectively. The effects of these microorganisms applied alone or with SS31 on plant growth promotion and root-knot nematode (RKN, Meloidogyne incognita) control was evaluated. In the duel culture tests, SS31 was only inhibited by B. subtilis, and when co-cultured in potato sucrose broth, the population of SS31 was also inhibited by B. subtilis and PSB. All microorganisms could be reisolated after 110 days from rhizosphere of water spinach and banana; SS31, B. subtilis, PSB, and NFB had more than 104 CFU/g soil, Trichoderma sp. more than 103 CFU, and mycorrhizal fungi more than 100 spores. When water spinach was inoculated with RKN, the population of Trichoderma sp. would decrease over time to 1.3 × 102 CFU/g soil. All the microorganism water suspensions did not lower RKN egg hatching rate, the water suspensions of Trichoderma sp. and NFB could lower RKN J2 infective ability, and PSB could decrease the attracting rate of water spinach root to RKN J2. On the other hand, SS31 soybean-sucrose cultured solution significantly decreased RKN egg hatching rate, infective ability, and the attracting rate of water spinach root to RKN J2. Commercial products of B. subtilis and PSB showed the effect on decreasing egg hatching rate and the attracting rate. Trichoderma sp. could lower both hatching rate and infective ability of RKN. When the microorganisms were cultured in rich broth or applied as commercial products, SS31, B. subtilis, Trichoderma sp. and PSB showed potential to control RKN. Suggesting the cultured substance and the secondary metabolites played an important role in disease control. In a 52 days green house test, microorganism cultured in rich solutions and commercial products also showed better efficacy than water suspension on RKN control and plant growth promotion. Single inoculated with SS31, PSB, NFB, and co-inoculated SS31 with Trichoderma sp., PSB, NFB, and mycorrhizal fungi in a 130 days green house test showed that applied microorganisms before RKN infection significantly decreased RKN population. The co-inoculated treatments could suppress RKN in soil better than single bioagent treatments. Among them, co-inoculation of SS31 and mycorrhizal fungi, after 70 and 110 days of inoculation, decreased RKN population to 17.7 and 127.7 J2/g soil, while the blank control treatment were 112.0 and 1678.0 J2/g soil. When bio-agents were added after RKN infection, they could also decrease RKN J2 population. In the 110 days green house test, co-inoculation of SS31 and B. subtilis was the best treatment for water spinach growth promotion; 110 days after inoculation, the above ground fresh weight (35.1 g) was twice more than the blank control treatment control (15.1 g). The results also showed co-inoculation treatments could help water spinach growth better than single bio-agent treatments. However, all treatments showed little effect on promoting banana plant growth; all treatments were no effect on soil pH values. Overall, co-inoculations of SS31 and other five microorganisms showed better effects on RKN control and plant growth promotion, but the results were not significantly different from each other. Based from my study, the result indicated that if microorganisms could coexist in the same environment, the synergy effect might not happen, so the cost effect of apply more than one bioagents need to be carefully evaluated.

‘Antibiotics’ begins by presenting a brief history of antibiotics, from the use of antimicrobials by indigenous populations to the discovery of penicillin by Alexander Fleming. By discovering the genus Streptomyces, Selman Waksman had identified the source of what was going to produce two-thirds of all antibiotics. Penicillin, sulphonamides, and streptomycin were all selectively toxic to bacteria without harming the human cells. The other major group of chemical antibacterials has been the quinolones and naphthyridines. We now have new methods of discovering antibiotics, including high-throughput screening and DNA sequencing.

Abstract From a human perspective, the most important biochemical feature of the streptomycetes is their capacity to make antibiotics. From the organism’s point of view, this is an adaptation to competition in the soil, with its teaming populations of microbes and small invertebrates of all kinds. The regulation of antibiotic production is a very sophisticated process, optimized over eons of natural selection to maximize the selective advantage of the organism.

Induced Systemic Resistance (ISR) is a highly variable property that can be induced by compost amendment of potting media and soils. For example, previous studies showed that only 1 of 79 potting mixes prepared with different batches of mature composts produced from several different types of solid wastes were able to suppress the severity of bacterial leaf spot of radish caused by Xanthomonas campestris pv. armoraciae compared with disease on plants produced in a nonamended sphagnum peat mix. In this project, microbial consortia in the rhizosphere of plants grown in ISR-active compost-amended substrates were characterized. The plants used included primarily cucumber but also tomato and radish. Rhizosphere microbial consortia were characterized using multiple molecular tools including DGGE (Israel) and T -RFLP (Ohio) in both ISR-active field plots and potting media. Universal as well as population-specific bacterial and fungal PCR primers were utilized. T -RFLP analyses using universal bacterial primers showed few significant differences in overall bacterial community composition in ISR-active and inactive substrates (Ohio). In addition, the community members which were significantly different varied when different ISR-activecomposts were used (Ohio). To better characterize the shifts in microbial community structure during the development of ISR, population specific molecular tools were developed (Israel, Ohio).-PCR primers were designed to detect and quantify bacterial groups including Pyrenomycetes, Bacillus, Pan toea, Pseudomonas, Xanthomonas and Streptomyces as well as Trichoderma and Fusarium; two groups of fungi that harbor isolates which are ISR active (Isreal and Ohio). Bacterial consortia associated with cucumber plants grown in compost-amended potting mixtures were shown to be dominated by the phylogenetic taxon Bacteroidetes, including members of the genus Chryseobacterium, which in some cases have been shown to be involved in biocontrol (Israel). Nested-PCR-DGGE analyses coupled with long l6S rDNA sequencing, demonstrated that the Chryseobacteriumspp. detected on seed and the root in compost-amended treatments were derived from the compost itself. The most effective ISR inducing rhizobacterial strains were identified as Bacillus sp. based on partial sequencing of l6S rDNA. However, these strains were significantly less effective in reducing the severity of disease than Trichoderma hamatum382 (T382). A procedure was developed for inoculation of a compost-amended substrate with T -382 which consistently induced ISR in cucumber against Phytophthora blight caused by Phytophthora capsiciand in radish against bacterial spot (Ohio). Inoculation of compost-amended potting mixes with biocontrol agents such as T -382 and other microbes that induce systemic resistance in plants significantly increased the frequency of systemic disease control obtained with natural compost amendments.

The main objective of this study was to develop data that would facilitate a consistently effective method of biological control of fire blight disease to be developed and to enable its implementation for disease control by ensuring its compatibility with variations in the biological, environmental, and chemical conditions present in pear orchards. As considerable information on the pathogen and biological control of fire blight was already gathered from studies in California and elsewhere, an emphasis was placed on investigating the genetics and ecology of Erwinia amylovora, the causal agent of fire blight in Israel. Studies of plasmid profile, virulence on several host, serological characteristics, as well as DNA fingerprints with selected primers all revealed E. amylovora strains in Israel to be homogeneous. Strains did vary in their resistance to streptomycin, with those from more northern locations being resistant while those in the southern costal plain were all sensitive to streptomycin. Resistance appeared to be conferred by chromosomal mutations as in streptomycin-resistant strains in California. The biological control agent Pseudomonas fluorescens strain A506 colonized flowers of both the Costia and Spodona pear cultivars in Israel as well as Bartlett pear in California. Flowers that were open at the time of spray inoculation of trees subsequently harbored from 105 to 107 cells of strain A506 per flower, while those that opened subsequent to spraying developed population sizes of about 105 cells/flower within 5 days. The incidence of fire blight infections were reduced about 3-fold in several trials in which moderate amounts of disease occurred in the plot areas; this degree of biological control is similar to that observed in California and elsewhere. On two occasions warm and moist weather that favored disease led to epidemics in which nearly all flowers became infected and which was so severe that neither P. fluorescens strain A506 nor chemical bactericides reduced disease incidence. A novel method for identifying antagonistic microorganisms for biological control of fire blight and other diseases was developed. A bacterial ice nucleation gene was introduced into E. amylovora to confer an Ice+ phenotype and the population sizes of this modified pathogen on flowers that had been pre-treated with potential control agents was estimated by measuring the freezing temperature of colonized flowers. Antagonistic strains that prevented the growth of E. amylovora in flowers were readily detected as those in which flowers froze at a low temperature. The method is both rapid and unbiased and several bacterial strains with substantial biological control potential have been identified using this method.

Campylobacter spp. are the most common bacterial cause of foodborne illness in the UK, with chicken considered to be the most important vehicle for this organism. The UK Food Standards Agency (FSA) agreed with industry to reduce Campylobacter spp. contamination in raw chicken and issued a target to reduce the prevalence of the most contaminated chickens (those with more than 1000 cfu per g chicken neck skin) to below 10 % at the end of the slaughter process, initially by 2016. To help monitor progress, a series of UK-wide surveys were undertaken to determine the levels of Campylobacter spp. on whole UK-produced, fresh chicken at retail sale in the UK. The data obtained for the first four years was reported in FSA projects FS241044 (2014/15) and FS102121 (2015 to 2018). The FSA has indicated that the retail proxy target for the percentage of highly contaminated raw whole retail chickens should be less than 7% and while continued monitoring has demonstrated a sustained decline for chickens from major retailer stores, chicken on sale in other stores have yet to meet this target. This report presents results from testing chickens from non-major retailer stores (only) in a fifth survey year from 2018 to 2019. In line with previous practise, samples were collected from stores distributed throughout the UK (in proportion to the population size of each country). Testing was performed by two laboratories - a Public Health England (PHE) laboratory or the Agri-Food &amp; Biosciences Institute (AFBI), Belfast. Enumeration of Campylobacter spp. was performed using the ISO 10272-2 standard enumeration method applied with a detection limit of 10 colony forming units (cfu) per gram (g) of neck skin. Antimicrobial resistance (AMR) to selected antimicrobials in accordance with those advised in the EU harmonised monitoring protocol was predicted from genome sequence data in Campylobacter jejuni and Campylobacter coli isolates The percentage (10.8%) of fresh, whole chicken at retail sale in stores of smaller chains (for example, Iceland, McColl’s, Budgens, Nisa, Costcutter, One Stop), independents and butchers (collectively referred to as non-major retailer stores in this report) in the UK that are highly contaminated (at more than 1000 cfu per g) with Campylobacter spp. has decreased since the previous survey year but is still higher than that found in samples from major retailers. 8 whole fresh raw chickens from non-major retailer stores were collected from August 2018 to July 2019 (n = 1009). Campylobacter spp. were detected in 55.8% of the chicken skin samples obtained from non-major retailer shops, and 10.8% of the samples had counts above 1000 cfu per g chicken skin. Comparison among production plant approval codes showed significant differences of the percentages of chicken samples with more than 1000 cfu per g, ranging from 0% to 28.1%. The percentage of samples with more than 1000 cfu of Campylobacter spp. per g was significantly higher in the period May, June and July than in the period November to April. The percentage of highly contaminated samples was significantly higher for samples taken from larger compared to smaller chickens. There was no statistical difference in the percentage of highly contaminated samples between those obtained from chicken reared with access to range (for example, free-range and organic birds) and those reared under standard regime (for example, no access to range) but the small sample size for organic and to a lesser extent free-range chickens, may have limited the ability to detect important differences should they exist. Campylobacter species was determined for isolates from 93.4% of the positive samples. C. jejuni was isolated from the majority (72.6%) of samples while C. coli was identified in 22.1% of samples. A combination of both species was found in 5.3% of samples. C. coli was more frequently isolated from samples obtained from chicken reared with access to range in comparison to those reared as standard birds. C. jejuni was less prevalent during the summer months of June, July and August compared to the remaining months of the year. Resistance to ciprofloxacin (fluoroquinolone), erythromycin (macrolide), tetracycline, (tetracyclines), gentamicin and streptomycin (aminoglycosides) was predicted from WGS data by the detection of known antimicrobial resistance determinants. Resistance to ciprofloxacin was detected in 185 (51.7%) isolates of C. jejuni and 49 (42.1%) isolates of C. coli; while 220 (61.1%) isolates of C. jejuni and 73 (62.9%) isolates of C. coli isolates were resistant to tetracycline. Three C. coli (2.6%) but none of the C. jejuni isolates harboured 23S mutations predicting reduced susceptibility to erythromycin. Multidrug resistance (MDR), defined as harbouring genetic determinants for resistance to at least three unrelated antimicrobial classes, was found in 10 (8.6%) C. coli isolates but not in any C. jejuni isolates. Co-resistance to ciprofloxacin and erythromycin was predicted in 1.7% of C. coli isolates. 9 Overall, the percentages of isolates with genetic AMR determinants found in this study were similar to those reported in the previous survey year (August 2016 to July 2017) where testing was based on phenotypic break-point testing. Multi-drug resistance was similar to that found in the previous survey years. It is recommended that trends in AMR in Campylobacter spp. isolates from retail chickens continue to be monitored to realise any increasing resistance of concern, particulary to erythromycin (macrolide). Considering that the percentage of fresh, whole chicken from non-major retailer stores in the UK that are highly contaminated (at more than 1000 cfu per g) with Campylobacter spp. continues to be above that in samples from major retailers more action including consideration of interventions such as improved biosecurity and slaughterhouse measures is needed to achieve better control of Campylobacter spp. for this section of the industry. The FSA has indicated that the retail proxy target for the percentage of highly contaminated retail chickens should be less than 7% and while continued monitoring has demonstrated a sustained decline for chickens from major retailer stores, chicken on sale in other stores have yet to meet this target.