Littérature scientifique sur le sujet « Physiological, Algal Protein »

c-AMP Dependent protein kinase (protein kinase A, PKA) is an important enzyme involved in the regulation of an increasing number of physiological processes including immune function, cardiovascular disease, memory disorders and cancer. The objective of this study was to evaluate the PKA inhibitory activity of a range of algal extracts, along with their fatty acid composition. Six algal species were investigated including two Chlorophyta ( Codium dimorphum and Ulva lactuca), two Phaeophyta ( Phyllospora comosa and Sargassum sp.) and two Rhodophyta ( Prionitis linearis and Corallina vancouveriensis), with the order of PKA inhibitory activity of their extracts identified as follows: brown seaweeds > red seaweeds > green seaweeds with the brown alga Sargassum sp. exhibiting the highest PKA inhibitory activity (84% at 100 μg/mL). GC/MS analysis identified a total of 18 fatty acids in the six algal extracts accounting for 72-87% of each extract, with hexadecanoic acid and 9,12-octadecadienoic acid as the dominant components. The most active extract ( Sargassum sp.) also contained the highest percentage of the saturated C14:0 fatty acid (12.8% of the total extract), which is a known to inhibit PKA. These results provide the first description of the PKA inhibitory activity of marine algae along with the first description of the fatty acid composition of these six algal species from South Eastern Australian waters. Importantly, this study reveals that abundant and readily available marine algae are a new and relatively unexplored source of PKA inhibitory compounds.

At present, there are few studies on known bacterial species and even less on fungi in biological algae control technology. In this paper, the green eutrophic shallow water lake Scenedesmus quadricauda (Turpin) was used as the research object, and white rot fungi, which has a high removal effect on water pollutants, algae and biological toxins, was used for algae control. The extent of the removal effect, physiological characteristics and the internal functional groups of the algae cells in the white rot fungi solution, the supernatant of the white rot fungi solution after centrifugation and the sterilized white rot fungi solution were investigated. The results showed that the best algae solubilization effect of the algae control system was achieved at 250 mg/L, with 8 mg/L of dissolved oxygen and a hydraulic retention time of 48 h. The average algae lysis rate was 85.48%, the average dehydrogenase activity reduction rate was 59.23%, the average soluble protein reduction rate was 65.16% and the average malondialdehyde content increased to 0.128 umol/L. After treatment with the white rot algae control system, the spatial structure of the Turpin cells was severely disrupted, and significant lysis occurred within the algal cells, forcing the release of intracellularly soluble substances, and reducing the dehydrogenase activity of the Turpin cells, thus inhibiting the growth activity of the algae cells. A further reduction in the soluble protein content reduces the nutrients required for the growth of Turpin, exacerbating the rate of reduction in the physiological metabolic activity of the Turpin cells and, ultimately, the inhibition or killing of the algal cells. The results of this research may provide theoretical guidance for the microbial control of water eutrophication; however, whether there will be secondary pollution after the algae dissolution of this process is worthy of further study.

An algal biofilm was employed as a novel kind of adsorbing material to remove Zn(II) from simulated wastewater. The algal biofilm system formed by Oedogonium sp. was operated in a dynamic mode for a period of 14 days with an initial Zn(II) concentration of 10 mg/L. The average effluent Zn(II) concentration was 0.247 mg/L and the average removal efficiency reached 97.7%. The effects of Zn(II) on key algal physiological and biochemical indices such as chlorophyll content, nitrate reductase and superoxide dismutase activity, extracellular polysaccharides (EPS), and soluble protein levels were studied. Our results showed that the algal biofilm could adapt to the simulated wastewater containing Zn(II). Scanning electron microscope and Fourier transform infrared spectroscopy analyses of algal biofilm revealed the presence of carboxyl, amino, and sulphonate groups, which were the main functional groups of EPS and proteins, and these were likely responsible for biosorption of the Zn(II) ions.

The potential to optimize wastewater utilization, whilst achieving satisfactory nutrient removal has been investigated through a simple system combining an Artificial Wetland with a High Rate Algal Pond (HRAP). Receiving septic sewage at a surface loading equivalent to 13.5 cm/day the Wetland achieved COD removals of 59.2%, NH4−N of 34,6%, PO4−P of 31.9% and SS of 78%. The HRAP selectively cultivated an easily harvestable filamentous green alga through a combination of short hydraulic residence times (< days), and microscreens as selectors over the effluent stream. Passage of the effluent through this stage permitted COD removal to increase to 79.4%, NH4−N to 82.8% and PO4−P to 54.1%, whilst generating a highly proteinaceous (42% by wt) biomass at a rate of approximately 50 tons/hectare/year. This paper discusses the performance of the pilot scale facility over a twelve month period, identifying biological and operational influences on the system, and the physiological mechanics by which the wastewater treatment is accomplished.

Abstract A comprehensive thioredoxin profile of Scenedesmus obliquus has been established by chromatography of heat-stable protein extracts on five different ion exchange, gel permeation, and affinity chromatography columns and using three different assay systems including homolo­gous S. obliquus ribonucleotide reductase, chloroplast fructose-bis-phosphatase, and NADP malate dehydrogenase. Four different thioredoxins were purified to homogeneity. Besides the large chloroplast thioredoxin f described previously, the algae contain three proteins of molecular weight 12,000 designated thioredoxin I, II, and III. They bind specifically to antibodies against E. coli thioredoxin. Chloroplast-free mutant algae (strain C-2A′) lack thioredoxin f but contain all three regular thioredoxins. Species I and II have very similar amino acid composition and enzyme-stimulating activities. They are considered cytoplasmic thioredoxins which serve as hydrogen donors in algal deoxyribonucleotide biosynthesis. Thioredoxin III is of low activity towards all the presently tested enzymes and its physiological role remains unknown; its role as a glutaredoxin could be excluded. All non-photosynthetic plant cells analyzed so far (mutant algae, seeds, and roots) contain a set of three regular-size thioredoxins.

In order to study the effects of nitrogen stress on the lipid synthesis of Parachlorella kessleri TY02 and to understand the changes in growth, photosynthetic pigments, total protein and total carbohydrate contents during lipid accumulation, the cells of the strain were cultured in nitrogen-deficient (N−) and nitrogen-rich (N+) media for one week. Changes in cell growth, chlorophyll content, chlorophyll fluorescence parameters, neutral lipid and total lipid content, total protein content and total carbohydrate content were measured and analyzed. The results showed that, under nitrogen stress, the algal strain grew slowly, and chlorophyll and total protein contents decreased, while total carbohydrate and total lipid contents increased. This indicated that, under nitrogen stress, most of the carbon flowed to the synthesis of lipids and carbohydrates. Meanwhile, reducing the nitrogen content was a relatively economical and easy to operate method of promoting lipid accumulation.

Colonization of land by plants was a major transition on Earth, but the developmental and genetic innovations required for this transition remain unknown. Physiological studies and the fossil record strongly suggest that the ability of the first land plants to form symbiotic associations with beneficial fungi was one of these critical innovations. In angiosperms, genes required for the perception and transduction of diffusible fungal signals for root colonization and for nutrient exchange have been characterized. However, the origin of these genes and their potential correlation with land colonization remain elusive. A comprehensive phylogenetic analysis of 259 transcriptomes and 10 green algal and basal land plant genomes, coupled with the characterization of the evolutionary path leading to the appearance of a key regulator, a calcium- and calmodulin-dependent protein kinase, showed that the symbiotic signaling pathway predated the first land plants. In contrast, downstream genes required for root colonization and their specific expression pattern probably appeared subsequent to the colonization of land. We conclude that the most recent common ancestor of extant land plants and green algae was preadapted for symbiotic associations. Subsequent improvement of this precursor stage in early land plants through rounds of gene duplication led to the acquisition of additional pathways and the ability to form a fully functional arbuscular mycorrhizal symbiosis.

Consumers can regulate the acquisition and use of nutrients through behavioral and physiological mechanisms. Here, we present an experimental approach that simultaneously integrates multiple nutritional traits, feeding assays, and juvenile performance to assess whether a marine herbivore (the amphipod Ampithoe valida) regulates the intake of elements (carbon and nitrogen), macronutrients (protein and non-protein) or both when offered freeze-dried tissues of seaweeds varying in nutritional content. We assessed behavioral regulation of nutrients in three ways. First, during no-choice assays, we found that amphipods ingested similar amounts of carbon, but not nitrogen, non-protein and protein, across algal diets. Second, herbivore intake rates of carbon, protein and non-protein components across no-choice assays was similar to intake rates when offered a choice of foods. Third, variation in intake rates of carbon and non-protein components among algal diets was significantly greater than was tissue content of these components, while variation in intake rates of nitrogen was significantly lower; differences in protein intake variation was equivocal. While these analytical approaches are not uniformly consistent, carbon and nitrogen seem to emerge as the nutrient components that are more strongly regulated by A. valida. Juveniles reared on single diets shown patterns of survivorship, growth and reproduction that could not be predicted by these feeding preferences, nor nutrient content. We conclude that an integrative approach that considers the intake of multiple nutrients potentially yields insights into feeding behavior and its performance consequences.

AbstractNitric oxide (NO) is a ubiquitous signalling molecule with widespread distribution in prokaryotes and eukaryotes where it is involved in countless physiological processes. While the mechanisms governing nitric oxide (NO) synthesis and signalling are well established in animals, the situation is less clear in the green lineage. Recent investigations have shown that NO synthase, the major enzymatic source for NO in animals, is absent in land plants but present in a limited number of algae. The first detailed analysis highlighted that these new NO synthases are functional but display specific structural features and probably original catalytic activities. Completing this picture, analyses were undertaken in order to investigate whether major components of the prototypic NO/cyclic GMP signalling cascades mediating many physiological effects of NO in animals were also present in plants. Only a few homologues of soluble guanylate cyclases, cGMP-dependent protein kinases, cyclic nucleotide-gated channels, and cGMP-regulated phosphodiesterases were identified in some algal species and their presence did not correlate with that of NO synthases. In contrast, S-nitrosoglutathione reductase, a critical regulator of S-nitrosothiols, was recurrently found. Overall, these findings highlight that plants do not mediate NO signalling through the classical NO/cGMP signalling module and support the concept that S-nitrosation is a ubiquitous NO-dependent signalling mechanism.

The need for clean and low-cost algae production demands for investigations on algal physiological response under different growth conditions. In this research, we investigated the growth, biomass production and biochemical composition of Chlorella vulgaris using semi-continuous cultures employing three growth media (LC Oligo, Chu 10 and WC media). The highest cell density was obtained in LC Oligo, while the lowest in Chu medium. Chlorophyll a, carbohydrate and protein concentrations and yield were highest in Chu and LC Oligo media. Lipid class analysis showed that hydrocarbons (HC), sterol esthers (SE), free fatty acids (FFA), aliphatic alcohols (ALC), acetone mobile polar lipids (AMPL) and phospholipids (PL) concentrations and yields were highest in the Chu medium. Triglyceride (TAG) and sterol (ST) concentrations were highest in the LC Oligo medium. The results suggested that for cost effective cultivation, LC Oligo medium is the best choice among those studied, as it saved the cost of buying vitamins and EDTA associated with the other growth media, while at the same time resulted in the best growth performance and biomass production.

A mangicultura é uma das atividades mais importantes para a fruticultura brasileira. Dentre as variedades produzidas, o cultivar \'Tommy Atkins\', sem dúvida, é o mais expressivo. Após a colheita, a qualidade fisiológica das mangas, geralmente, é mantida pela integração de técnicas de controle físico e aplicação de moléculas com atividade biológica contra microrganismos, a exemplo dos fungicidas aplicados no controle do fungo Colletotrichum gloeosporioides, agente causal da antracnose, principal doença na fase de pós-colheita de mangas. Entretanto, atualmente há forte pressão da população para a utilização de moléculas que deixem nenhum ou o mínimo possível de resíduos em alimentos, especialmente os consumidos in natura. Vários produtos são vendidos no Brasil como biofertilizantes, mas, estes apresentam também, a capacidade de mitigar estresses bióticos e abióticos, inerentes da vida pós-colheita de frutas. Nesse contexto, pode-se citar o extrato da alga marinha Ascophyllum nodosum (Acadian®) e o fosfito de potássio (Phytogard®), utilizados em vários passos do processo de produção agrícola, mostrando respostas diversas sobre os vegetais tratados. Ambos os produtos apresentam baixa toxicidade ao homem e ao ambiente e não são fitotóxicos. Assim, com a ideia de gerar informação mais acertada acerca dos processos envolvidos a partir da utilização desses produtos, na cadeia produtiva da manga, este trabalho foi construído sobre três vertentes principais. A primeira parte, objetivou verificar o efeito in vitro do extrato da alga marinha A. nodosum e do fosfito de potássio sobre a morfofisiologia do fungo C. gloeosporioides isolado de mangas, variedade \'Tommy Atkins\'. Na segunda parte, o objetivo do trabalho foi avaliar o efeito do extrato da alga marinha A. nodosum e do fosfito de potássio, ambos aplicados em diferentes concentrações, sobre o parasitismo do fungo 1 em mangas \'Tommy Atkins\', na perspectiva da indução de resistência, na fase de pós-colheita desses frutos. Finalmente, na terceira parte do trabalho, objetivou-se verificar o efeito do extrato da alga marinha A. nodosum e do fosfito de potássio, ambos aplicados em diferentes concentrações, sobre características físicas e químicas de mangas \'Tommy Atkins\', na fase de pós-colheita. Como resultados da primeira parte do trabalho, observou-se que o extrato de algas induz o crescimento e a esporulação do fungo, inibindo, contudo, a germinação e a fixação de conídios produzidos pelo patógeno. O fosfito de potássio interfere no crescimento e esporulação do microrganismo e inibe a germinação e adesão de conídios produzidos por C. gloeosporioides. Os dois produtos alteram a permeabilidade seletiva da membrana plasmática da hifa e incrementam a atividade das enzimas β-1,3-glucanase e quitinase na estrutura. Entretanto, somente o extrato de algas interferiu no conteúdo total de proteínas da hifa, aumentando esse parâmetro. Os dois produtos diminuíram a atividade celulolítica de C. gloeosporioides. Na segunda parte, os resultados demonstraram que, tanto para o extrato de algas quanto para o fosfito de potássio, houve diminuição do tamanho da lesão, da velocidade de crescimento da lesão e da AACPD. Além disso, foram observados incrementos em todos os parâmetros bioquímicos analisados, o que indicou que os produtos têm efeito indutor de resistência em mangas. Finalmente, como resultados para a terceira parte do trabalho, foi evidenciado que tanto o extrato de algas quanto o sal de potássio, em todas as concentrações utilizadas, ajudaram na redução da perda de massa dos frutos, retardaram a diminuição do ângulo de cor da polpa (ângulo Hue) e a firmeza desta. Além disso, os produtos testados desaceleraram a perda de acidez da polpa e mantiveram elevados os valores de ácidos orgânicos, a exemplo do ácido cítrico; mantiveram abaixo do tratamento controle o conteúdo de sólidos solúveis (°Brix), mas não interferiram no total de carboidratos encontrados nas cascas dos frutos. Conclusivamente, o extrato de A. nodosum e o fosfito de potássio, retardam o amadurecimento e senescência de mangas na fase de pós-colheita, reduzem a severidade da antracnose nos frutos pela indução de resistência e ainda, apresentam efeitos diretos sobre o fungo C. gloeosporioides. Dessa maneira, os produtos podem ser utilizados como mantenedores da qualidade fisiológica de mangas \'Tommy Atkins\', pois minimizam os estresses de ordem biótica e abiótica relativos à vida pós-colheita dessas frutas.
Mango farming is one of the most important activities for Brazilian fruit growing. Among the varieties produced, the cultivar \'Tommy Atkins\' is undoubtedly the most expressive. After harvesting, the physiological quality of mangoes is generally maintained by the integration of physical control techniques and the application of molecules with biological activity against microorganisms, such as the fungicides applied in the control of the fungus Colletotrichum gloeosporioides, the causal agent of anthracnose, the main disease in the postharvest phase of mangoes. However, there is currently strong population pressure for the use of molecules that leave none or the least possible residues in food, especially those consumed in natura. Several products are sold in Brazil as biofertilizers, but also present the ability to mitigate biotic and abiotic stresses inherent of the postharvest fruit life. Ascophyllum nodosum seaweed extract (Acadian®) and potassium phosphite (Phytogard®), both used in several steps of the agricultural production process, can be mentioned in this context, showing different responses on treated plants. Both products have low toxicity to man and the environment and are not phytotoxic. Thus, in order to generate precise information about the processes involved in the use of these products, in the production chain of mango, this work was built on three main strands. The first part aimed to verify the in vitro effect of the A. nodosum seaweed extract and the potassium phosphite on the morphophysiology of the fungus C. gloeosporioides isolated from mangoes \'Tommy Atkins\'. In the second part, the objective of this work was to evaluate the effect of A. nodosum seaweed extract and the potassium phosphite, both applied in different concentrations, on the parasitism of the fungus C. gloeosporioides in mangoes \'Tommy Atkins\', from the perspective of induction of resistance in the postharvest phase of these fruits. Finally, in the third part of the work, the objective was to verify the effect of A. nodosum seaweed extract and of the potassium phosphite, both applied in different concentrations, on physical and chemical characteristics of \'Tommy Atkins\' mangoes in the postharvest stage. As results of the first part of this work, it was observed that the algae extract induces the growth and sporulation of the fungus; however, it inhibits the germination and adhesion of conidia produced by the pathogen. Potassium phosphite interferes with the growth and sporulation of the microorganism and inhibits the germination and adhesion of conidia produced by C. gloeosporioides. The two products alter the selective permeability of hypha plasma membrane and increase the activity of the enzymes β-1,3-glucanase and chitinase in the structure. However, only the algae extract interfered in the total protein content of the hypha, increasing this parameter. The two products decreased the cellulolytic activity of C. gloeosporioides. In the second part, the results demonstrated that, for both algae extract and potassium phosphite, there was a decrease in lesion diameter, lesion growth rate and AUDPC. In addition, increments were observed in all biochemical parameters analyzed, which indicated that the products have resistance-inducing effect on mangoes. Finally, as results for the third part of the work, it was evidenced that both the algae extract and the potassium salt, in all the concentrations used, helped to reduce the loss of mass of the fruits, delayed the decrease of pulp color angle (Hue angle) and the firmness of this. In addition, the products tested decelerated the loss of acidity of the pulp and maintained high values of organic acids, as citric acid; controlled soluble solids content in relation to the control (°Brix), but did not interfere in the total carbohydrate found in the fruit peels. Conclusively, the A. nodosum extract and potassium phosphite, delay the maturation and senescence of mangoes in the post-harvest phase, reduce the severity of the anthracnose in the fruits by the induction of resistance and also have direct effects on the fungus C. gloeosporioides. In this way, the products can be used to maintain the physiological quality of \'Tommy Atkins\' mangoes, since they minimize the biotic and abiotic stresses related to the postharvest life of these fruits.

La fotosintesi è il principale sistema di conversione dell’energia luminosa sul nostro pianeta. In tutti gli organismi fotosintetici come piante, alghe e cianobatteri, la fotosintesi si svolge nelle membrane tilacoidi dei cloroplasti, e permette di convertire l'energia solare in energia chimica, utilizzata per trasformare l'anidride carbonica in biomassa, producendo ossigeno come sottoprodotto. L'energia luminosa può essere anche dannosa, se in eccesso può determinare le sovraeccitazione dei fotosistemi, e la conseguente produzione di specie reattive dell'ossigeno (ROS), molecole tossiche che danneggiano seriamente la cellula. Per evitare questa situazione critica, gli organismi fotosintetici regolano l’apparato fotosintetico, attivando diversi meccanismi fotoprotettivi. A livello della membrana tilacoidale, vi sono complessi proteici chiamati fotosistemi, con un sistema antenna (Light Harvesting Complex – LHCs), in grado di raccogliere e trasformare l’energia luminosa. Le proteine LHCs hanno un duplice fondamentale ruolo: la raccolta della luce e la regolazione dell'energia di eccitazione, per evitare la sovrasaturazione dei fotosistemi. La strategia fotoprotettiva più rapida e importante è la dissipazione termica dell’energia luminosa assorbita in eccesso, meccanismo chiamato Non-Photochemical-Quenching (NPQ), attivato da un gradiente protonico (DpH) fra le membrane tilacoidi. Nelle piante superiori, il processo di NPQ dipende dalla proteina PSBS. Nelle microalghe invece, come per la specie modello Chlamydomonas reinhardtii, è indispensabile la proteina LhcSR: proteina che lega pigmenti come clorofilla e xantofille, sensibile a pH acidi, quencher degli stati eccitati delle clorofille, con un rapido decadimento di fluorescenza. Nelle microalghe, il meccanismo di NPQ è davvero influente: fino al 80% di energia luminosa assorbita può essere dissipata sotto forma di calore, con la conseguente perdita di produttività in biomassa a favore della fotoprotezione. Lo studio del meccanismo di NPQ, permette di individuare una strategia promettente per la domesticazione delle microalghe, migliorandone la produttività. La domesticazione è indispensabile a fini commerciali: per la produzione di biomassa algale per l’alimentazione umana/animale, per l’estrazione di sostanze chimiche e farmaceutiche per la produzione di biocarburanti. Per questi motivi, il punto centrale della tesi è lo studio del meccanismo di NPQ nelle microalghe. Nella prima parte, il meccanismo NPQ è stato dettagliatamente studiato in sei diverse specie, alcune planctoniche, altre in aggregazione in biofilm. Sono state considerate misure di fluorescenza, variazione nel profilo di pigmenti e formazione di DpH transmembrana; ed è stato dimostrato l'eterogeneità del meccanismo di NPQ nelle alghe verdi: il comportamento di NPQ non è collegato alla posizione filogenetica, ma piuttosto alla pressione selettiva dell’ambientale in cui esse vivono. Alcune specie presentano un meccanismo NPQ-zeaxantina-dipendente, come per le piante superiori, mentre la correlazione è assente in altre specie algali dello stesso gruppo filogenetico. In un sistema biologico si potrebbe notevolmente aumentare produttività e biomassa, riducendo il livello di dissipazione termica dell’energia luminosa (NPQ). Per dimostrare questa ipotesi teorica, è stato studiata la correlazione tra produzione di biomassa, NPQ e accumulo di LhcSR, proteina cruciale nell’attivazione di questo fenomeno nella specie modello Chlamydomonas reinhardtii. Ceppi wild type e mutanti knock-out con ridotta induzione di NPQ, sono stati coltivati simultaneamente in un sistema di fotobioreattori, a diverse condizioni di intensità luminose. Il ceppo mutante senza le subunità proteiche di LhcSR3, presenta un ridotto livello di NPQ, e una migliore capacità di convertire fotoni in biomassa rispetto al WT. Pertanto questa è la dimostrazione che la produttività algale può essere aumentata diminuendo il livello di NPQ. Un secondo ceppo mutante senza alcun gene LhcSR (LhcSR3 e LhcSR1), con meccanismo di NPQ completamente abolito, mostra una produttività molto inferiore rispetto a WT: un livello fotoprotettivo minimo è quindi necessario. Chalmydomonas reinhardtii in condizioni di elevato irraggiamento converte l’energia luminosa a bassa efficienza, dissipando l’eccesso termicamente. In questa situazione il livello fotoprotettivo nel cloroplasto è elevato con un basso rischio di fotoinibizione, a scapito però della produzione di biomassa. In Chlamydomonas reinhardtii la proteina chiave indispensabile per l’attivazione del meccanismo di NPQ è LhcSR. In aggiunta ci sono altre proteine coinvolte, appartenenti alla famiglia LHCBM, deputate alla raccolta della luce e prevalentemente legate al fotosistema II (PSII). I geni LHCBM sono nove, altamente conservati, e nonostante l’elevata omologia, la funzione non è ridondante: alcune proteine LHCBM esercitano un ruolo ben specifico e definito. Ad esempio, LHCBM1ha un ruolo nel meccanismo di NPQ, probabilmente come partner dell'elemento regolatore principale LhcSR3, mentre LHCBM2 / 7 è coinvolta nell’induzione delle transizioni di stato. La funzione delle subunità LHCBM4, LHCBM6 e LHCBM8 è ancora sconosciuta, per questo motivo, in questo lavoro le caratteristiche biochimiche e spettroscopiche di LHCBM4, LHCBM6 e LHCBM8 sono state analizzate utilizzando proteine ricombinanti in vitro, la funzione fisiologica è stata poi studiata in-vivo utilizzando ceppi amiRNA. I risultati dimostrano il silenziamento delle subunità LHCBM4, LHCBM6 e LHCBM8, suggerendo il loro coinvolgimento nei meccanismi di fotoprotezione. Come illustrato in precedenza, la modulazione dei fenomeni NPQ, è un fattore chiave per la domesticazione delle microalghe. Le informazioni note per l'organismo modello Chlamydomonas reinhardtii sono state utilizzate su specie ad interesse commerciale, come l’alga oleaginosa Nannochloropsis gaditana, appartenente alla classe delle Eustigmatophyceae, di interesse applicativo nel campo della produzione di biocarburanti. N. gaditana è caratterizzata da un elevato contenuto lipidico (fino a 65-70% sul peso secco) e da un rapido tasso di crescita. In questo lavoro, è stata effettuata una mutagenesi chimica, ed è stato utilizzato un metodo basato sulla fluorescenza della clorofilla emessa per esaminare il gran numero di colonie, isolando quelle con variazioni in parametri fotosintetici. 2100 cloni indipendenti sono stati analizzati, tre cloni sono risultati interessanti per la riduzione delle dimensioni dell’antenna fotosintetica del PSII o per un basso livello di dissipazione termica dell’energia luminosa (NPQ). E’ stato caratterizzato il fenotipo dei mutanti selezionati e valutata l’efficienza di utilizzo dell’energia luminosa. Il fenomeno di Non-Photochemical-quenching (NPQ) è un meccanismo fisiologico chiave per tutte le cellule fotosintetiche. È essenziale per la corretta modalità di funzionamento del processo fotosintetico, perché permette di controllare il livello di clorofille tripletto e la produzione di ROS nel cloroplasto. Il processo NPQ è un meccanismo fotoprotettivo complesso: può cambiare nello stesso gruppo filogenetico algale, in base alla condizioni ambientali in cui si sono evolute. Nel processo di NPQ, diversi fattori chiave agiscono insieme: DpH transmembrana, pigmenti e proteine quencher. Il fattore più importante coinvolto nell’NPQ in C. reinhardtii è la proteina LhcSR, che può interagire con altre proteine quencher accessorie, come LHCBM1 e LHCBM6. In questa tesi è stato dimostrato che si può incrementare la produttività algale diminuendo il livello di dissipazione termica dell’energia luminosa (Non-Photochemical-Quenching NPQ) garantendo contemporaneamente un minimo livello di fotoprotezione. Con una migliore comprensione del meccanismo NPQ è possibile trovare il modo per domesticare le microalghe, eliminando il divario fra biomassa teorica e realmente ottenibile.
Photosynthesis is the main solar energy converting system on our planet. In all photosynthetic organisms, photosynthesis takes place in the thylakoid membranes of chloroplasts, which are capable of converting solar energy into chemical energy to fix carbon dioxide into biomass, producing oxygen as a byproduct. Light energy, which intensity and spectral quality change continuously in the environment, can also be harmful since excess irradiances can determine the photosystems over-excitation, with the consequent production of Reactive Oxygen Species (ROS). ROS are toxic molecules that can seriously damage the chloroplast as well as the entire cell. In order to avoid this critical situation, several photoprotective mechanisms evolved. Light harvesting and energy conversion by charge separation occur at the level of membrane protein complexes called Photosystems. In eukaryotic systems, the Light Harvesting Complex (LHCs) multigene family constitutes the pigment binding antenna system of photosystems. LHCs play two fundamental roles in photosynthesis: light harvesting and regulation of excitation energy. The fastest and most important photoprotective inducible strategy is the activation of the thermal dissipation of light energy absorbed in excess, a mechanism called Non-Photochemical-Quenching (NPQ), which is triggered by the generation of a pH gradient across thylakoid membranes. In vascular plants, NPQ depends on the Lhc-like protein PSBS, while a different polypeptide called LhcSR, is required in algae as the model species Chlamydomonas reinhardtii. LhcSR is a chlorophyll and xanthophyll-binding protein, responsive to low pH and it is a strong quencher of Chl excited states, exhibiting a fast fluorescence decay. In microalgae, the NPQ mechanism is really influent: up to 80% of absorbed light energy can be dissipated as heat, with consequent loss of light use efficiency and biomass productivity in favor of photoprotection. This explains the importance of the study of NPQ, in order to find a promising way of domestication to improve overall algal productivity. Algae domestication is an indispensible step for their commercial applications, such as production of biomass for human/animal feeding or extraction of high-value chemicals and biofuels feedstock. For all these reasons, the central point of this thesis is the study of NPQ in microalgae. In the first part of the thesis, the NPQ mechanism was studied in detail in six different green algae, some are planktonic species, others live in aggregation on biofilm structures. The analysis takes into consideration fluorescence measurements, the change in the pigment profiling and the transmembrane DpH formation. From this investigation, the heterogeneity of the NPQ mechanism was demonstrated in green algae: the NPQ behavior was not related to the phylogeny of the algae but rather to the environmental selection pressure. Some green algae present a zeaxanthin-dependent-NPQ, like the vascular plants, while the correlation is absent in other algal species of the same phylogenic group. In a biologic system the productivity and biomass accumulation could be considerably increased by reducing the level of energy dissipation into heat. In order to demonstrate this theoretic hypothesis, the attention was focused on the study of the correlation between biomass production, heat dissipation (NPQ) and the accumulation of LhcSR, which is the crucial protein in triggering NPQ in the model species for algae research Chlamydomonas reinhardtii. Wild type strain and knockout mutants with reduced NPQ induction were grown simultaneously in a small scale photobioreactor, in different conditions of light intensity. The main conclusion of this work is that a mutant in the two genes coding for LhcSR3 subunit, with reduced NPQ induction, showed an improved capacity to convert photons into biomass than the WT. Therefore this is the demonstration that algal productivity can be increased by down-regulating NPQ. On the other hand a second mutant in which NPQ induction was completely abolished by knocking out also the gene coding for LhcSR1, showed a much lower productivity compared to WT: a minimal level of photoprotective quenching is thus necessary. Therefore our results demonstrate that evolution led Chalmydomonas reinhardtii cells to promptly switch upon high irradiance exposure to energy converting states with low efficiency in order to safely dissipate the energy absorbed in excess through heat. Chloroplasts in a highly quenched state are less efficient in photosynthetic biomass production, but they are in a safer photoprotective state with a low risk for Photoinhibition. In Chlamydomonas reinhardtii NPQ is fully dependent on the presence of the LhcSR polypeptide. In addition there are likely other proteins involved among members of the LHCBM family, namely Light Harvesting Complexes subunits predominantly associated with PSII. In Chlamydomonas reinhardtii there are nine highly conserved LHCBM genes: some of them exert a specific role, with a well defined, non-redundant function despite their high homology, while for other genes their functions are still unclear. For example, a role in NPQ was demonstrated for LHCBM1 protein, likely as a partner for the main regulator element LhcSR3, while LHCBM2/7 was reported to be involved in state transitions induction. The specific function of LHCBM4, LHCBM6 and LHCBM8 polypeptide is still unknown, for all these reasons, in this work the biochemical and spectroscopic features of LHCBM4, LHCBM6 and LHCBM8 were first analyzed in the recombinant proteins in vitro and their physiologic function was then studied in vivo by a reverse-genetic approach using amiRNA strains. The results demonstrate the quenching activity of LHCBM4, LHCBM6 and LHCBM8, suggesting their involvement in photoprotective mechanisms. As shown previously, the modulation of the NPQ phenomena, is a key factor for microalgae domestication. The information obtained for the model organism Chlamydomonas reinhardtii was then applied in the case of commercial interesting species. The Eustigmatophyceae oleaginous alga Nannochloropsis gaditana is important for biofuel production: it is characterized by a high oil content (up to 65-70% oil on dry weight) and fast growth in a wide range of conditions. In this work a chemical mutagenesis was done, and time-resolved chlorophyll a fluorescence imaging was used to investigate a large number of colonies and to isolate those with changes in photosynthetic parameters. We analyzed 2100 independent clones, among them we identified three interesting clones for low antenna size of PSII or for a low energy quenching dissipation. Several experiments were done to characterize the phenotype of the selected mutants in order to evaluate their possible increase in light use efficiency. Non-Photochemical-Quenching (NPQ) is a key physiologic mechanism in all photosynthetic cells. It is essential for the correct mode of operation of the photosynthetic process controlling the level of chlorophyll triplets and the ROS production in the chloroplast. The NPQ process is a complex photoprotective mechanism: it can change in the same phylogenetic group of algal species in dependence of the environmental pressure. There are several key factors, which act together, the transmembrane DpH, the xanthophyll pigments, and quencher protein(s). The most important actor involved in NPQ in C. reinhardtii is LhcSR, which can interact with accessory LHC quencher proteins, like LHCBM1 and LHCBM6. In this thesis there is a demonstration that algal productivity can be increased by down-regulating NPQ ensuring to the cells a minimal level of photoprotective quenching. With a better understanding of the NPQ mechanism it is possible to find a way for algae domestication, in order to fill the gap between the theoretic biomass estimation and the real obtainable biomass yield.

Edible seaweeds (macroalgae and microalgae) are considered superfoods of our waterways. Based on pigmentation seaweeds, macroalgae are classified into three groups, green seaweeds (Chlorophyta), brown seaweeds (Phaeophyta) and red seaweeds (Rhodophyta). Seaweeds are rich in macro and micro nutrients. They contain protein, dietary fiber, minerals, vitamins, polyphenols, peptides, sterols and polyunsaturated fatty acids. Apart from being a major nutritional source in the human diet, seaweed is considered a functional and nutraceutical due to its extra nutritional and physiological properties. Plethora of bioactive compounds with potential applications in food, medicinal, health and pharmaceutical industries are included in extensive research and industries. For example, phycocolloids from seaweeds are widely used in the food industry. Medicinal and pharmaceutical properties of edible seaweeds include anti-tumor property, anti-viral property, anti-coagulant property, anti-Alzheimer’s property, and anti-oxidant property. Thus, a vast scope of investigating and understanding bioactive compounds from edible seaweeds is welltimed.

In order to meet the ever-growing global demands for food, healthcare, and energy, among other sources, the twenty-first century has seen a significant surge in the use of microalgae. They have seen applications in varied industries ranging from pharmaceuticals to energy to even the food industry, where its role as a source of proteins shines the most among other bioactive compounds. The microalgal biomass has the innate ability to grow in varied ecological conditions and has diverse compositions. While not economically competitive with fossil fuels or other renewable energy sources such as solar and wind, microalgal sources are technically viable, and a multitude of resources and time have been poured into the research of microalgal renewable fuels (biodiesel, ethanol, hydrogen, etc.). The rich diversity of microalgae, which is still underutilized, provides a variety of physiologically active metabolites of economic importance. These bioactive metabolites have antioxidant, antibacterial, antifungal, antiviral, anti-inflammatory, and anticancer properties. The microalgal biomass is a rich source of various compounds such as fatty acids, carotenoids, polysterols, and phenolics that can be utilized to synthesize pharmaceutical compounds and other nutraceuticals. Considering microalgae as a superfood, space food, functional food, strong agent for detoxification with high content of micro and macronutrients has found potential application in occupational, systematic, and life style disorders subsequently enhancing immunity. The path from algal research to the launching of new food products or dietary supplements is strongly affected by industrial, regulatory, and nutritional considerations. Our purpose is to review and assess what is known about different food components (i.e., proteins, polysaccharides, lipids, vitamins, minerals, and antioxidants, potential toxicants) in the context of improving knowledge about the efficacy of algal foods as nutraceuticals. This review will add be an asset for food, pharma, nutra, and cosmetic sector.