Engineering the glycogen metabolism in cyanobacterial photosynthetic cell factories: a review / 生物工程学报

Cyanobacteria are important photosynthetic autotrophic microorganisms and are considered as one of the most promising microbial chassises for photosynthetic cell factories. Glycogen is the most important natural carbon sink of cyanobacteria, playing important roles in regulating its intracellular carbon distributions. In order to optimize the performances of cyanobacterial photosynthetic cell factories and drive more photosynthetic carbon flow toward the synthesis of desired metabolites, many strategies and approaches have been developed to manipulate the glycogen metabolism in cyanobacteria. However, the disturbances on glycogen metabolism usually cause complex effects on the physiology and metabolism of cyanobacterial cells. Moreover, the effects on synthesis efficiencies of different photosynthetic cell factories usually differ. In this manuscript, we summarized the recent progress on engineering cyanobacterial glycogen metabolism, analyzed and compared the physiological and metabolism effects caused by engineering glycogen metabolism in different cyanobacteria species, and prospected the future trends of this strategy on optimizing cyanobacterial photosynthetic cell factories.

Heterologous expression and function evaluation of Gloeobacter violaceus rhodopsin in Escherichia coli / 生物工程学报

Proton-pumping rhodopsin (PPR) is a simple photosystem widely distributed in nature. By binding to retinal, PPR can transfer protons from the cytoplasmic to the extracellular side of the membrane under illumination, creating a proton motive force (PMF) to synthesize ATP. The conversion of light into chemical energy by introducing rhodopsin into nonphotosynthetic engineered strains could contribute to promoting growth, increasing production and improving cell tolerance of microbial hosts. Gloeorhodopsin (GR) is a PPR from Gloeobacter violaceus PCC 7421. We expressed GR heterologously in Escherichia coli and verified its functional activity. GR could properly function as a light-driven proton pump and its absorption maximum was at 539 nm. We observed that GR was mainly located on the cell membrane and no inclusion body could be found. After increasing expression level by ribosome binding site optimization, intracellular ATP increased, suggesting that GR could supply additional energy to heterologous hosts under given conditions.

Métodos de extração, estabilidade e biodisponibilidade da guanitoxina em cultivos de Sphaeropermopsis torques-reginae analisadas por espectrometria de massas / Methods of extraction, stability, and bioavailability of guanitoxin in Sphaeropermopsis torques-reginae cultures analyzed by mass spectrometry

A guanitoxina (GNT) é uma neurotoxina produzida por algumas cepas de cianobactérias dos gêneros Dolichospermum e Sphaerospermopsis>. A GNT é o único organofosforado natural, capaz de causar a morte de animais selvagens e domésticos devido à inibição irreversível da acetilcolinesterase. Apesar de sua alta toxicidade, o diagnóstico da GNT em amostras biológicas ainda é um grande desafio. A dificuldade para sua detecção está diretamente ligada à sua instabilidade em altas temperaturas e pH alcalino, tornando difícil seu monitoramento em corpos d'água. Por isso, esta pesquisa objetivou estudar a estabilidade e biodisponibilidade da GNT em amostras aquosas, com intuito de obter mais informações sobre a natureza química e biológica dessa potente neurotoxina. Para realizar este estudo, a cepa ITEP-24 (S. torques-reginae) produtora de GNT foi cultivada em laboratório sob condições controladas, para obter biomassa para os experimentos de extração, semi-isolamento, estabilidade, ensaio in vitro e identificação por LC-MS/MS. Primeiramente foram realizados testes de extração da GNT partir de células liofilizadas da cepa ITEP-24 utilizando água, metanol e etanol em pH ácido. Depois utilizou-se dois métodos de extração em fase sólida (SPE) com cartuchos preenchidos com fases estacionarias C18 em fase reversa e sílica gel em fase normal, com objetivo de avaliar qual método de SPE seria melhor para extrair e concentrar a GNT. Nós também testamos métodos para lisar as células com sondas de ultrassom, misturador e centrifugação. Além dos métodos de extração, nós avaliamos a estabilidade da toxina em diferentes temperaturas, para isso a biomassa seca contendo a GNT ficou condicionada a 4 °C, 23 °C, -20 °C, -80 °C durantes seis meses, e análises de identificação foram realizadas dentro período de 150 dias em uma sequência de 30 dias. A estabilidade da toxina foi analisada também a partir de extrações em soluções com diferentes valores de pH (1,5; 3,0; 5,0; 7,0; 8,5; 10,5) e temperatura (23 ºC e 37 ºC). Depois, analisou-se a biodisponibilidade da GNT em células frescas da linhagem ITEP-24 através de teste de dissolução in vitro. O objetivo deste teste foi avaliar a liberação da toxina intracelular em meio simulado do conteúdo gástrica e intestinal com e sem enzimas digestivas para compreender e estimar a disponibilidade da GNT in vivo. Os resultados de todos experimentos descritos neste estudo, foram obtidos a partir de análises por cromatografia líquida de interação hidrofílica (HILIC) acoplado ao espectrômetro de massas do tipo triplo quadrupolo LC-QqQ-MS/MS utilizando as transições 253>58, 253>159 e 159>58 [M+H]+ utilizando coluna com fase estacionária zwitteriônica (ZIC). A identificação da GNT foi realizada também por cromatografia líquida acoplada ao espectrômetro de massas de alta resolução (LC-HR-QTOF-MS) com coluna Luna C18, Hydro-RP C18 e ZIC-HILIC. Dos protocolos de extração testados, a combinação de metanol/água (70:30 v/v) com ácido acético (0.3%) extraiu maior quantidade relativa da GNT a partir de células frescas e liofilizadas da cepa ITEP-24 e a concentração da toxina foi maior em amostras de células frescas. Em relação aos métodos de lise celular, as extrações realizadas em sonda de ultrassom com banho-maria e centrifugação por 1h foram estatisticamente significantes para liberar a toxina intracelular. Não houve diferença significativa entre os testes de SPE, no entanto, a semipurificação da toxina foi melhor com cartucho preenchido com sílica gel em fase normal e adaptação desse método em coluna aberta permitiu obter uma fração enriquecida com GNT. A GNT mostrou ser mais estável em pH ácido, sendo o pH 3,0 o melhor para manter e extrair a toxina em amostras aquosas e a toxina intracelular presente em células secas podem degradar em temperatura de 23 °C por um período de 150 dias mesmo em solução com pH 3,0. Durante os testes de extração e purificação foi observado também a degradação da toxina em processos de secagem e ressuspensão. As análises realizadas no LC-HR-QTOF-MS com diferentes métodos cromatográficos possibilitou a identificação da GNT, porém o método realizado com coluna ZIC-HILIC mostrou melhor resolução cromatográfica dos picos relativos m/z e tempo de retenção de toxina. Os resultados obtidos nos testes de dissolução in vitro mostraram que a GNT fica mais disponível no simulado gástrico com e sem a enzima pepsina, mas também pode ser absorvida no intestino. Portanto, o teste de dissolução in vitro pode ser uma ferramenta útil para a avaliação de risco de cianotoxinas in vivo, devido ao seu potencial de monitorar qualitativa e quantitativamente substâncias dissolvidas em fluidos gastrointestinais. Os resultados apresentados neste estudo fornecem informações valiosas para uma melhor compreensão da estabilidade e biodisponibilidade do GNT. Além disso, os métodos apresentados neste estudo podem ser úteis para diversas aplicações projetadas para identificar a toxina em amostras ambientais, bem como orientações para procedimentos de purificação da GNT

Guanitoxin (GNT) is a neurotoxin produced by some strains of cyanobacteria of the genus Dolichospermum and Sphaerospermopsis. GNT is the only natural organophosphate, capable of causing the death of animals from wild and domestic animals due to irreversible inhibition of acetylcholinesterase. Despite its high toxicity, the diagnosis of GNT in biological samples is still a significant challenge. The difficulty in its detection is directly linked to its instability at high temperatures and alkaline pH, making it difficult to monitor in bodies of water. Therefore, this research aimed to study the stability and bioavailability of GNT in aqueous samples to provide more information about the chemical and biological nature of this molecule. The strain ITEP-24 (S. torques-reginae) producing GNT was grown in the laboratory under controlled conditions to obtain biomass for the extraction, semi-isolation, stability, in vitro tests, and toxin identification by LC-MS/MS. Firstly, tests were carried out to extract GNT from lyophilized cells strain ITEP-24 using water, methanol, and ethanol at acidic pH and, two SPE methods in cartridges with stationary phases of C18 reverse phase and normal phase gel silica, to evaluate which would be better to extract and concentrate the GNT. We also tested different methods of cell lysis, such as ultrasound probes, mixers, and centrifugation. In addition to the extraction methods, the stability of the toxin was evaluated at different temperatures, for this, the dry biomass containing the toxin was conditioned at 4 °C, 23 °C, -20 °C, -80 °C for 150 days and analysis of the identification of the GNT was carried out within that period in a sequence of 30 days. The toxin stability was also analyzed from extractions in solutions with different pH values (1.5; 3.0; 5.0; 7.0; 8.5; 10.5) and temperature (23 ºC and 37 ºC). In addition, we performed dissolution tests with fresh cells of the ITEP-24 strain to evaluate the bioavailability of GNT in simulated gastric and intestinal fluids with and without digestive enzymes to understand and estimate the availability of GNT in vivo. The results of all experiments described in this study were obtained from analyzes by hydrophilic interaction liquid chromatography (HILIC) coupled to the LC-QqQ-MS/MS triple quadrupole mass spectrometer using the transitions m/z 253> 58, m/z 253> 159 and m/z 159> 58 [M + H]+ using a column with the zwitterionic stationary phase (ZIC). Liquid chromatography coupled to the high-resolution mass spectrometer (LC-HR-QTOF-MS) with Luna column C18, Hydro-RP C18, and ZIC-HILIC carried out the identification of the GNT. From the extraction protocols tested, the combination of methanol/water (70:30 v/v) with acetic acid (0.3%) extracted a greater relative amount of GNT from fresh and lyophilized ITEP-24 cells, and the concentration of the toxin is higher previously fresh. Concerning cellular methods, the ultrasound probe with a water bath and centrifugation for 1h ware statistically significant to release the intracellular toxin. There was no significant difference between the SPE tests. However, the semi-purification of the toxin was better with a cartridge filled with gel silica in the normal phase and adaptation of this method in an open column allowed to obtain a fraction enriched with GNT. GNT was more stable at acid pH, with pH 3.0 being the best to maintain and the intracellular toxin present in dry cells can degrade at a temperature at 23 °C for 150 days even in pH 3.0 solution. The toxin can also hydrolyze in the drying and resuspension processes. The analyzes carried out in LC-HR-QTOF-MS with different chromatographic methods made it possible to identify the GNT itself, however, the ZIC-HILIC column method showed excellent chromatographic resolution of the relative m/z peaks and toxin retention time. The results obtained in the in vitro dissolution tests showed that GNT is more available in the gastric simulation with and without the enzyme pepsin, but it can also be absorbed in the intestine. Thus, in vitro dissolution tests can be used as a useful tool for the risk assessment of cyanotoxins in vivo due to their potential to qualitatively and quantitatively monitor substances dissolved in gastrointestinal fluids. The results presented in this study provide valuable information for a better understanding of the stability and bioavailability of GNT. Besides, the methods presented in this study can be useful for various applications designed to identify the toxin in environmental samples, as well as guidance on procedures for purifying GNT

Bacterial degradation of dissolved organic matter released by Planktothrix agardhii (Cyanobacteria) / Degradação bacteriana da matéria orgânica dissolvida liberada por Planktothrix agardhii (Cyanobacteria)

Abstract Although Planktothrix agardhii often produces toxic blooms in eutrophic water bodies around the world, little is known about the fate of the organic matter released by these abundant Cyanobacteria. Thus, this study focused in estimating the bacterial consumption of the DOC and DON (dissolved organic carbon and dissolved organic nitrogen, respectively) produced by axenic P. agardhii cultures and identifying some of the bacterial OTUs (operational taxonomic units) involved in the process. Both P. agardhii and bacterial inocula were sampled from the eutrophic Barra Bonita Reservoir (SP, Brazil). Two distinct carbon degradation phases were observed: during the first three days, higher degradation coefficients were calculated, which were followed by a slower degradation phase. The maximum value observed for particulate bacterial carbon (POC) was 11.9 mg L-1, which consisted of 62.5% of the total available DOC, and its mineralization coefficient was 0.477 day-1 (t½ = 1.45 days). A similar pattern of degradation was observed for DON, although the coefficients were slightly different. Changes in the OTUs patterns were observed during the different steps of the degradation. The main OTUs were related to the classes Alphaproteobacteria (8 OTUs), Betaproteobacteria (2 OTUs) and Gammaproteobacteria (3 OTUs). The genus Acinetobacter was the only identified organism that occurred during the whole process. Bacterial richness was higher at the slower degradation phase, which could be related to the small amounts of DOM (dissolved organic matter) available, particularly carbon. The kinetics of the bacterial degradation of P. agardhii-originated DOM suggests minimal loss of DOM from the Barra Bonita reservoir.

Resumo Embora Planktothrix agardhii frequentemente forme florações tóxicas em corpos d'água pelo mundo, pouco ainda se sabe sobre o destino da matéria orgânica liberada por essa abundante Cyanobacteria. Assim, este estudo foi focado na estimativa do consumo bacteriano do carbono orgânico dissolvido (DOC) e nitrogênio orgânico dissolvido (DON) produzido por culturas axênicas de P. agardhii e identificação de algumas das unidades taxonômicas operacionais (OTUs) bacterianas envolvidas no processo. Ambos a linhagem de P. agardhii e o inóculo bacteriano foram amostrados do reservatório eutrófico de Barra Bonita (SP, Brasil). Foram observadas duas fases distintas da degradação do DOC: durante os três primeiros dias, coeficientes mais altos de degradação foram calculados, que foram então seguidos por uma fase mais lenta da degradação do carbono. O valor máximo calculado para o carbono bacteriano particulado (POC) foi de 11,9 mgL-1, o que equivale a aproximadamente 62,5% do DOC disponível para consumo, e o seu coeficiente de mineralização foi de 0,477 dia-1 (t1/2 = 1,45 dias). Um padrão similar de degradação foi observado para DON, embora os coeficientes sejam ligeiramente diferentes. Foram observadas mudanças nos padrões de OTUs durante os diferentes passos da degradação. As principais OTUs foram relacionadas às classes Alphaproteobacteria (8 OTUs), Betaproteobacteria (2 OTUs) e Gammaproteobacteria (3 OTUs). O gênero Acinetobacter foi o único organismo identificado que ocorreu durante todo o processo. A maior riqueza bacteriana foi observada durante a fase lenta de degradação, o que pode estar relacionado às pequenas quantidades de matéria orgânica dissovida (DOM) disponíveis, particularmente o carbono. A cinética da degradação bacteriana da MOD de P. agardhii, quando comparada ao tempo de retenção do reservatório, sugere que existe uma perda mínima após sua liberação em Barra Bonita.

Degradation of textile dyes by cyanobacteria

Abstract Dyes are recalcitrant compounds that resist conventional biological treatments. The degradation of three textile dyes (Indigo, RBBR and Sulphur Black), and the dye-containing liquid effluent and solid waste from the Municipal Treatment Station, Americana, São Paulo, Brazil, by the cyanobacteria Anabaena flos-aquae UTCC64, Phormidium autumnale UTEX1580 and Synechococcus sp. PCC7942 was evaluated. The dye degradation efficiency of the cyanobacteria was compared with anaerobic and anaerobic-aerobic systems in terms of discolouration and toxicity evaluations. The discoloration was evaluated by absorption spectroscopy. Toxicity was measured using the organisms Hydra attenuata, the alga Selenastrum capricornutum and lettuce seeds. The three cyanobacteria showed the potential to remediate textile effluent by removing the colour and reducing the toxicity. However, the growth of cyanobacteria on sludge was slow and discoloration was not efficient. The cyanobacteria P. autumnale UTEX1580 was the only strain that completely degraded the indigo dye. An evaluation of the mutagenicity potential was performed by use of the micronucleus assay using Allium sp. No mutagenicity was observed after the treatment. Two metabolites were produced during the degradation, anthranilic acid and isatin, but toxicity did not increase after the treatment. The cyanobacteria showed the ability to degrade the dyes present in a textile effluent; therefore, they can be used in a tertiary treatment of effluents with recalcitrant compounds.

Photosynthesis at the far-red region of the spectrum in Acaryochloris marina

Acaryochloris marina is an oxygenic cyanobacterium that utilizes far-red light for photosynthesis. It has an expanded genome, which helps in its adaptability to the environment, where it can survive on low energy photons. Its major light absorbing pigment is chlorophyll d and it has α-carotene as a major carotenoid. Light harvesting antenna includes the external phycobilin binding proteins, which are hexameric rods made of phycocyanin and allophycocyanins, while the small integral membrane bound chlorophyll binding proteins are also present. There is specific chlorophyll a molecule in both the reaction center of Photosystem I (PSI) and PSII, but majority of the reaction center consists of chlorophyll d. The composition of the PSII reaction center is debatable especially the role and position of chlorophyll a in it. Here we discuss the photosystems of this bacterium and its related biology.

Effect of UV-C on thylakoid arrangement, pigment content and nitrogenase activity in the cyanobacterium Microchaete sp.

The effect of UV-C radiation on thylakoid arrangement, chlorophyll-a and carotenoid content and nitrogenase activity of the cyanobacterium Microchaete sp. was studied. Chlorophyll-a and carotenoid content increased gradually up to 48 h of UV-C exposure but declined with longer exposures. Nitrogenase activity decreased moderately with 6 to 12 h exposure and decreased substantially afterwards. When cells exposed to UV-C for 12 to 24 h, grown under fluorescent light for 144 h, nitrogenase activity increased to levels greater than in the control cells. The exposure of UV-C treated cells to fluorescent light, however, did not result in recovery of pigment content. In Microchaete sp. cells treated with UV-C for 144 h, thylakoid membranes became dense, were aggregated into bundles, and were surrounded by spaces devoid of cytoplasm.

Biodiesel production from marine cyanobacteria cultured in plate and tubular photobioreactors.

Carbon (neutral) based renewable liquid biofuels are alternative to petroleum derived transport fuels that contribute to global warming and are of a limited availability. Microalgae based biofuels are considered as promising source of energy. Lyngbya sp. and Synechococcus sp. were studied for the possibility of biodiesel production in different media such as ASNIII, sea water enrichment medium and BG11. The sea water enrichment medium was found superior in enhancing the growth rate of these microalgae. Nitrogen depletion has less effect in total chlorophyll a content, at the same time the lipid content was increased in both Lyngbya sp. and Synechococcus sp. by 1.4 and 1.2 % respectively. Increase in salinity from 0.5-1.0 M also showed an increase in the lipid content to 2.0 and 0.8 % in these strains; but a salinity of 1.5 M has a total inhibitory effect in the growth. The total biomass yield was comparatively higher in tubular LED photobioreactor than the fluorescent flat plated photobioreactor. Lipid extraction was obtained maximum at 60 ºC in 1:10 sample: solvent ratio. GC-MS analysis of biodiesel showed high content of polyunsaturated fatty acids (PUFA; 4.86 %) than saturated fatty acid (SFA; 4.10 %). Biodiesel production was found maximum in Synechococcus sp. than Lyngbya sp. The viscosity of the biodiesel was closely related to conventional diesel. The results strongly suggest that marine microalgae could be used as a renewable energy source for biodiesel production.

Evalúan las probables propiedades terapéuticas de la espirulina / Assessment of the probable therapeutic properties of spirulina

La espirulina es un alga verdeazulada (cianobacteria) que ha sido consumida por los seres humanos durante cientos de años en la región Kanem de Chad y en las regiones lacustres de México. Actualmente se comercializa en todo el mundo como alimento terapéutico. Su potencial como tratamiento de varias enfermedades se encuentra en evaluación. El consumo mundial de espirulina ha clarificado tanto sus potenciales efectos adversos como sus acciones beneficiosas. En este artículo se presenta un breve resumen del uso de la espirulina en el área de la salud.

In vivo quality control of photosystem II in cyanobacteria Synechocystis sp. PCC 6803: D1 protein degradation and repair under the influence of light, heat and darkness.

The cells of Synechocystis sp. PCC 6803 were subjected under photoinhibitory irradiation (600 micromolm(-2)s(-1)) at various temperatures (20-40 degrees C) to study in vivo quality control of photosystem II (PSII). The protease biogenesis and its consequences on photosynthetic efficiency (chlorophyll fluorescence ratio Fv/Fm) of the PSII, D1 degradation and repair were monitored during illumination and darkness. The loss in Fv/Fm value and degradation of D1 protein occurred not only under high light exposure, but also continued when the cells were subjected under dark restoration process after high light exposure. No loss in Fv/Fm value or D1 degradation occurred during recovery under growth/low light (30 micromol m(-2) s(-1)). Further, it helped the resynthesis of new D1 protein, essential to sustain quality control of PSII. In vivo triggering of D1 protein required high light exposure to switch-on the protease biosynthesis to maintain protease pool which induced temperature-dependent enzymatic proteolysis of photodamaged D1 protein during photoinhition and dark incubation. Our findings suggested the involvement and overexpression of a membrane-bound FtsH protease during high light exposure which caused degradation of D1 protein, strictly regulated by high temperature (30-40 degrees C). However, lower temperature (20 degrees C) prevented further loss of photoinhibited PSII efficiency in vivo and also retarded temperature-dependent proteolytic process of D1 degradation.

Antioxidant activity of Aulosira fertilisima on CCl4 induced hepatotoxicity in rats.

Free radicals cause cell injury, when they are generated in excess or when the antioxidant defense is impaired. Carbon tetrachloride (CCl4) is used as a model for liver injury. In this study antioxidant activity of ethanol extract of A. fertilisima (EEA) was investigated using CCl4 intoxicated rat liver as the experimental model. Oral administration of EEA at a dose of 100 mg/kg body weight, for 14 consecutive days, the rate of the production of antioxidant enzymes like super oxide dismutase, catalase, glutathione peroxidase and glutathione transferase in rats compared to the CCl4 treated group without any supporting treatment. Liver damage is detected by the measurement of the activities of serum enzymes like aspartate aminotransferase, alanine aminotransferase, gamma glutamyl transpeptidase and alkaline phosphatase which were released in to the blood from damaged cells. The normalization of these enzymes levels was observed in rats treated with EEA (100 mg/kg body weight) by reducing the leakage of the above enzymes in to the blood. The findings provide a rationale for further studies on isolation of active principles and its pharmacological evaluation. Protection offered by silymarin (standard reference drug) seemed relatively greater.

PCR-based detection of microcystin-producing cyanobacterial blooms from Central India.

Microcystin synthetase-gene-specific primers were used to identify hepatotoxic microcystin producing genotypes in six Microcystis spp.-dominant water blooms. Four blooms gave positive PCR reaction. They produced microcystin-RR and -LR amounting to 0.037 to 0.095% of the dry mass.

Mycosporine-like amino acids (MAAs): chemical structure, biosynthesis and significance as UV-absorbing/screening compounds.

Continuous depletion of the stratospheric ozone layer has resulted in an increase in ultraviolet-B (UV-B; 280-315 nm) radiation on the earth's surface which inhibits photochemical and photobiological processes. However, certain photosynthetic organisms have evolved mechanisms to counteract the toxicity of ultraviolet or high photosynthetically active radiation by synthesizing the UV-absorbing/screening compounds, such as mycosporine-like amino acids (MAAs) and scytonemin besides the repair of UV-induced damage of DNA and accumulation of carotenoids and detoxifying enzymes or radical quenchers and antioxidants. Chemical structure of various MAAs, their possible biochemical routes of synthesis and role as photoprotective compounds in various organisms are discussed.

Experimental and bioinformatic approaches for analyzing and visualizing cyanobacterial nitrogen and hydrogen metabolism

Many cyanobacteria are capable of utilizing light energy for nitrogen fixation. As a by-product of this nitrogenase mediated catalysis, hydrogen gas is produced. Several approaches to increase hydrogen production from cyanobacteria exist. Usually, these approaches are non-targeted. Here we exemplify how DNA-microarray based gene-expression analysis and bioinformatic visualization techniques can be used to analyze nitrogen and hydrogen metabolism from the filamentous, heterocyst forming cyanobacterium Nostoc PCC 7120. We analyzed the expression of 1249 genes from major metabolic categories under nitrogen fixing and non-nitrogen fixing growth. Of the selected genes, 494 show a more than 2-fold expression difference in the two conditions analyzed. Under nitrogen-fixing conditions 465 genes, mainly involved in energy metabolism, photosynthesis, respiration and nitrogen-fixation, were found to be stronger expressed, whereas only 29 genes showed a stronger expression under non-nitrogen fixing conditions. To help understanding probe hybridization, all expression data were correlated with potential target secondary structures and probe GC-content. For the first time the expression of high light-induced stress proteins (HLIP-family) is shown to be linked to the nitrogen availability.

Effect of UV-B on photosynthesis, membrane lipids and MAAs in marine cyanobacterium, Phormidium corium (Agardh) Gomont.

UV-B radiation (0.8 +/- 0.1 mW cm(-2)) and UV-B radiation supplemented with low intensity PAR (approximately 80 micro mol m(-2) s(-1)) affected photosynthesis at the level of antenna system as well as PS II reaction centre (Fo and Fm declined) in Phormidium corium (Agardh) Gomont. UV-B radiation resulted in decline in sugar content, peroxidation of membrane lipids as well as quantitative and qualitative changes in phosphoglycolipids and neutral lipids. Fatty acid profile did not show any qualitative changes due to the treatment, however, UV-B supplemented with low PAR resulted in slightly higher level of unsaturation. P. corium synthesized MAAs in response to UV-B. Quantity of MAAs increased when UV-B treatment was supplemented with low level PAR.

A simple method for efficient extraction and purification of C-phycocyanin from Spirulina platensis Geitler.

Phycocyanin is a major light harvesting accessory pigment of red algae and cyanobacteria. In the light of its many commercial applications in food and pharmaceutical industry, purity of the pigment plays a major role. Pharmaceutical industry demands a highly pure phycocyanin with A620/280 ratio of 4 and food industry a ratio of 2. In the present study phycocyanin was extracted in sodium phosphate buffer (pH 7) after macerating in liquid nitrogen. The crude phycocyanin thus extracted was precipitated with 50% ammonium sulphate, purified by dialysis and finally by gel filtration chromatography. Pure phycocyanin was finally obtained with an A620/A280 value of 4.98.

Scavenging of nickel and chromium toxicity in Aulosira fertilissima by immobilization: effect on nitrogen assimilating enzymes

The ubiquity of heavy metals in the biosphere results in the introduction of high amounts of toxic metals into the food chain from various sources. In the present study, one of the strongest nitrogen fixing cyanobacterium of the rice fields, Aulosira fertilissima, was subjected to nickel and chromium stress and the ameliorating effect of immobilization was investigated. Cell immobilization could protect the organism's growth against the toxicity of both heavy metals at LC50 as compared to lethal concentrations. The nitrate reductase activity in free cells treated with the metals was substantially inhibited but immobilized cells treated with 0.1 ppm nickel was not affected by the metal treatment. Cell immobilization also resulted in a significant protection against sub-lethal concentration of chromium but to a lesser degree than it did with sub- lethal levels of nickel. Control immobilized cells also had higher Nitrogenase activity than control free cells. Nickel and chromium addition markedly decreased the enzyme activity in free cells but immobilized cells exposed to sublethal concentrations of both metals could overcome this decrease. Glutamine synthetase showed similar response under immobilized conditions compared to free cells with both metals. The addition of algal filtrate in 3:1 ratio further increased the nitrogenase activity compared with immobilized cells treated with sublethal doses of both metals. Immobilization facilitated higher uptake of nickel as compared to chromium. The observations of the present study clearly demonstrate the protective effect of immobilization on Aulosira fertilissima against Nickel and chromium toxicity. Rice field ecosystem thus possess a bidirectional natural metal ameliorating system where Aulosira mats act as a naturally immobilized system and the decay of Aulosira along with other cyanobacteria act as natural chelators protecting the rice plants from deleterious effects of the heavy metals. Most importantly is...

Alginate immobilization of Spirulina platensis for wastewater treatment.

Immobilization of cyanobacterium Spirulina platensis in sodium alginate (1.5 %) gave the best quality of bead and 15-16 beads were formed per mL of aqueous solution of alginate. The immobilized cells were used in a batch process for treatment of diluted sewage. After 8 days, 95 % of BOD5, 77 % of COD, 90 % of ammonia, and 94 % of TSS were removed.

Induction of polyunsaturated fatty-acid synthesis enhances tolerance of a cyanobacterium, Cylindrospermopsis raciborskii, to low-temperature photoinhibition.

Acyl-lipid desaturation introduces double bonds (unsaturated bonds) at specifically defined positions of fatty acids that are esterified to the glycerol backbone of membrane glycerolipids. Desaturation pattern of the glycerolipids of Cylindrospermopsis raciborskii (C. raciborskii), a filamentous cyanobacterial strain, was determined in cells grown at 35 degrees C and 25 degrees C. The lowering of the growth temperature from 35 degrees C to 25 degrees C resulted in a considerable accumulation of polyunsaturated octadecanoic fatty acids in all lipid classes. Lipid unsaturation of C. raciborskii was also compared to Synechocystis PCC6803. In C. raciborskii cells, a shift in growth temperature induced a much more pronounced alteration in the desaturation pattern of all lipid classes than in Synechocystis PCC6803. The tolerance to low-temperature photoinhibition of the C. raciborskii cells grown at 25 degrees C and 35 degrees C was also compared to the tolerance of Synechocystis cells grown at the same temperatures. Lower growth temperature increased the tolerance of C. raciborskii cells but not that of Synechocystis cells. These results strengthen the importance of polyunsaturated glycerolipids in the tolerance to environmental stresses and may give a physiological explanation for the determinative role of C. raciborskii strain in algal blooming in the Lake Balaton (Hungary).

Carbon concentration mechanisms in photosynthetic microorganisms.

Unicellular green algae and cyanobacteria have mechanism to actively concentrate dissolved inorganic carbon into the cells, only if they are grown with air levels of CO2. The carbon concentration mechanisms are commonly known as "CCM" or "DIC-pumps". The DIC-pumps are environmental adaptation that function to actively transport and accumulate inorganic carbon (HCO3- and CO2; Ci) within the cell and then uses this Ci pool to actively increase the concentration of CO2 at the site of ribulose bisphosphate carboxylase-oxygenase (Rubisco), the primary CO2-fixing enzyme. The current working model for dissolved inorganic carbon concentration mechanism in unicellular green algae includes several isoforms of carbonic anhydrase (CA), and ATPase driven active transporters at the plasmalemma and at the inner chloroplast envelopes. In the past fifteen years, significant progress has been made in isolating and characterizing the various isoforms of carbonic anhydrase at the biochemical and molecular level. However, we have an inadequate understanding of active transporters that are located on the plasmalemma and at the chloroplast envelopes. In this mini-review we focus on certain aspects of the induction, function and significance of the dissolved inorganic carbon concentration mechanisms in aquatic photosynthetic microorganisms.