Insight to biotechnological utility of phycochemicals from cyanobacterium Anabaena sp.: An overview.

Cyanobacteria (blue-green algae) are well-known for the ability to excrete extra-cellular products, as a variety of cyanochemicals (phycocompounds) of curio with several extensive therapeutic applications. Among these phycocompound, the cyanotoxins from certain water-bloom forming taxa are toxic to biota, including crocodiles. Failure of current non-renewable source compounds in producing sustainable and non-toxic therapeutics led the urgency of discovering products from natural sources. Particularly, compounds of the filamentous N2-fixing Anabaena sp. have effective antibacterial, antifungal, antioxidant, and anticancer properties. Today, such newer compounds are the potential targets for the possible novel chemical scaffolds, suitable for mainstream-drug development cascades. Bioactive compounds of Anabaena sp. such as, anatoxins, hassallidins and phycobiliproteins have proven their inherent antibacterial, antifungal, and antineoplastic activities, respectively. Herein, the available details of the biomass production and the inherent phyco-constituents namely, alkaloids, lipids, phenols, peptides, proteins, polysaccharides, terpenoids and cyanotoxins are considered, along with geographical distributions and morphological characteristics of the cyanobacterium. The acquisitions of cyanochemicals in recent years have newly addressed several pharmaceutical aliments, and the understanding of the associated molecular interactions of phycochemicals have been considered, for plausible use in drug developments in future.

Production of polyhydroxybutyrate by the cyanobacterium cf. Anabaena sp.

Polyhydroxybutyrate (PHB) production by the cyanobacterium cf. Anabaena sp. was here studied by varying the medium composition and the carbon source used to induce mixotrophic growth conditions. The highest PHB productivity (0.06 gPHB gbiomass-1 d-1) was observed when cultivating cf. Anabaena sp. in phosphorus-free medium and in the presence of sodium acetate (5.0 g L-1 concentration), after an incubation period of 7 days. A content of 40% of PHB on biomass, a dry weight of 0.1 g L-1, and a photosynthetic efficiency equal to the control were obtained. The cyanobacterium was then grown on a larger scale (10 L) to evaluate the characteristics of the produced PHB in relation to the main composition of the biomass (the content of proteins, polysaccharides, and lipids): after an incubation period of 7 days, a content of 6% of lipids (52% of which as unsaturated fatty acids with 18 carbon atoms), 12% of polysaccharides, 28% of proteins, and 46% of PHB was reached. The extracted PHB had a molecular weight of 3 MDa and a PDI of 1.7. These promising results demonstrated that cf. Anabaena sp. can be included among the Cyanobacteria species able to produce polyhydroxyalkanoates (PHAs) either in photoautotrophic or mixotrophic conditions, especially when it is grown under phosphorus-free conditions.

A TonB-Like Protein, SjdR, Is Involved in the Structural Definition of the Intercellular Septa in the Heterocyst-Forming Cyanobacterium Anabaena.

Cyanobacteria are photosynthetic organisms with a Gram-negative envelope structure. Certain filamentous species such as Anabaena sp. strain PCC 7120 can fix dinitrogen upon depletion of combined nitrogen. Because the nitrogen-fixing enzyme, nitrogenase, is oxygen sensitive, photosynthesis and nitrogen fixation are spatially separated in Anabaena. Nitrogen fixation takes place in specialized cells called heterocysts, which differentiate from vegetative cells. During heterocyst differentiation, a microoxic environment is created by dismantling photosystem II and restructuring the cell wall. Moreover, solute exchange between the different cell types is regulated to limit oxygen influx into the heterocyst. The septal zone containing nanopores for solute exchange is constricted between heterocysts and vegetative cells, and cyanophycin plugs are located at the heterocyst poles. We identified a protein previously annotated as TonB1 that is largely conserved among cyanobacteria. A mutant of the encoding gene formed heterocysts but was impaired in diazotrophic growth. Mutant heterocysts appeared elongated and exhibited abnormal morphological features, including a reduced cyanophycin plug, an enhanced septum size, and a restricted nanopore zone in the septum. In spite of this, the intercellular transfer velocity of the fluorescent marker calcein was increased in the mutant compared to the wild type. Thus, the protein is required for proper formation of septal structures, expanding our emerging understanding of Anabaena peptidoglycan plasticity and intercellular solute exchange, and is therefore renamed SjdR (septal junction disk regulator). Notably, calcium supplementation compensated for the impaired diazotrophic growth and alterations in septal peptidoglycan in the sjdR mutant, emphasizing the importance of calcium for cell wall structure. IMPORTANCE Multicellularity in bacteria confers an improved adaptive capacity to environmental conditions and stresses. This includes an enhanced capability of resource utilization through a distribution of biochemical processes between constituent cells. This specialization results in a mutual dependency of different cell types, as is the case for nitrogen-fixing heterocysts and photosynthetically active vegetative cells in Anabaena. In this cyanobacterium, intercellular solute exchange is facilitated through nanopores in the peptidoglycan between adjacent cells. To ensure functionality of the specialized cells, septal size as well as the position, size, and frequency of nanopores in the septum need to be tightly established. The novel septal junction disk regulator SjdR characterized here is conserved in the cyanobacterial phylum. It influences septal size and septal nanopore distribution. Consequently, its absence severely affects the intercellular communication and the strains' growth capacity under nitrogen depletion. Thus, SjdR is involved in septal structure remodeling in cyanobacteria.

Functional and mechanistic insights into the differential effect of the toxicant 'Se(IV)' in the cyanobacterium Anabaena PCC 7120.

Selenium, an essential trace element for animals, poses a threat to all forms of life above a threshold concentration. The ubiquitously present cyanobacteria, a major photosynthetic biotic component of aquatic and other ecosystems, are excellent systems to study the effects of environmental toxicants. The molecular changes that led to beneficial or detrimental effects in response to different doses of selenium oxyanion Se(IV) were analyzed in the filamentous cyanobacterium Anabaena PCC 7120. This organism showed no inhibition in growth up to 15 mg/L sodium selenite, but above this dose i.e. 20-100 mg/L of Se(IV), both growth and photosynthesis were substantially inhibited. Along with the increased accumulation of non-protein thiols, a consistent reduction in levels of ROS was observed at 10 mg/mL dose of Se(IV). High dose of Se(IV) (above 20 mg/L) enhanced endogenous reactive oxygen species (ROS)/lipid peroxidation, and decreased photosynthetic capability. Treatment with 100 mg/L Se(IV) downregulated transcription of several photosynthesis pathways-related genes such as those encoding photosystem I and II proteins, phycobilisome rod-core linker protein, phycocyanobilin, phycoerythrocyanin-associated proteins etc. Interestingly, at a dose range of 10-15 mg/L Se(IV), Anabaena showed an increase in PSII photosynthetic yield and electron transport rate (at PSII), suggesting improved photosynthesis. Se was incorporated into the Anabaena cells, and Se-enriched thylakoid membranes showed higher redox conductivity than the thylakoid membranes from untreated cells. Overall, the data supports that modulation of photosynthetic machinery is one of the crucial mechanisms responsible for the dose-dependent contrasting effect of Se(IV) observed in Anabaena.

Alleviation of carbon tetrachloride-induced hepatocellular damage and oxidative stress in rats by Anabaena oryzae phycocyanin.

Phycocyanin isolated from Anabaena biomass was in-vitro assayed for its antioxidant activity against DPPH (2,2-diphenyl-1-picrylhydrazyl) and ABTS [2,2'-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid)] free radical, revealing maximum activities amounting to 77 and 80% at 1,000 µg/ml and SC50 values about 96 and 111 µg/ml, respectively. A biological experiment was conducted, involving 40 male Wistar Albino rats, divided into five groups. Group I received only the basal diet as a normal control, while groups II, III, IV, and V were administrated intraperitoneal (IP) injection of a single dose of CCl4 (50% in corn oil) at 0.5 ml/kg body weight. Subsequently, groups II, III, IV, and V received phycocyanin at 0.0, 25, 50, and 100 mg/kg body weight/day. CCl4 induced considerable increases (p < .05) in the levels of serum ALT, AST, urea and creatinine, total lipid, and triglycerides coupled with significant reductions (p < .05) in serum antioxidant enzymes and some liver histopathological deformations compared to the negative control (group 1). Administration of Anabaena oryzae phycocyanin can counteract these CCl4 -induced changes. PRACTICAL APPLICATIONS: Phycocyanin isolated from Anabaena has beneficial effects such as the antioxidant, antibacterial, anticancer, and hepatoprotective effect. Phycocyanin may play a key role in alleviating oxidative stress, artificially induced by carbon tetrachloride in Albino rats, to ultimately determine its capacity to serve as a natural antioxidant for food and health applications.

Phytohormone up-regulates the biochemical constituent, exopolysaccharide and nitrogen metabolism in paddy-field cyanobacteria exposed to chromium stress.

BACKGROUND: Cyanobacteria are well known for their inherent ability to serve as atmospheric nitrogen fixers and as bio-fertilizers; however, increased contaminants in aquatic ecosystem significantly decline the growth and function of these microbes in paddy fields. Plant growth regulators play beneficial role in combating the negative effects induced by heavy metals in photoautotroph. Current study evaluates the potential role of indole acetic acid (IAA; 290 nm) and kinetin (KN; 10 nm) on growth, nitrogen metabolism and biochemical constituents of two paddy field cyanobacteria Nostoc muscorum ATCC 27893 and Anabaena sp. PCC 7120 exposed to two concentrations of chromium (CrVI; 100 µM and 150 µM). RESULTS: Both the tested doses of CrVI declined the growth, ratio of chlorophyll a to carotenoids (Chl a/Car), contents of phycobiliproteins; phycocyanin (PC), allophycocyanin (APC), and phycoerythrin (PE), protein and carbohydrate associated with decrease in the inorganic nitrogen (nitrate; NO3- and nitrite; NO2-) uptake rate that results in the decrease in nitrate and ammonia assimilating enzymes; nitrate reductase (NR), nitrite reductase (NiR), glutamine synthetase (GS), glutamate synthase (GOGAT) except glutamate dehydrogenase (GDH). However, exogenous supplementation of IAA and KN exhibited alleviating effects on growth, nitrogen metabolism and exopolysaccharide (EPS) (first protective barrier against metal toxicity) contents in both the cyanobacteria, which probably occurred as a result of a substantial decrease in the Cr uptake that lowers the damaging effects. CONCLUSION: Overall result of the present study signifies affirmative role of the phytohormone in minimizing the toxic effects induced by chromium by stimulating the growth of cyanobacteria thereby enhancing its ability as bio-fertilizer that improved fertility and productivity of soil even in metal contaminated condition.

Assessment of the antioxidant and anticancer potential of different isolated strains of cyanobacteria and microalgae from soil and agriculture drain water.

The potential usage of cyanobacteria and microalgae as a promising and alternative source for new and safe therapeutic compounds is recently caught the attention, due to its versatile properties as antitumor, antioxidant, antifungal, and antiviral agents. Primarily, the cyanobacteria and microalgae from fresh and marine water are previously studied, however those isolated from soil and agriculture drain water were poorly investigated. Therefore, this study aimed to screen and characterize the antioxidant profile, as well as the potential anticancer assessment of 12 species of cyanobacteria and two species of microalgae strains isolated from soil and agriculture drain water. The data showed that total phenol contents were highest in Anabaena oryzae and Aphanizomenon gracile (27.39 and 26.83 mg GAE/g, respectively), followed by Leptolyngbya fragilis (22.96 mg GAE/g). Out of the 14 species identified, the cyanobacterium Dolichospermum flos-aquae HSSASE2 exhibited the most elevated antioxidant activity in terms of NO scavenging activity and anti-lipid peroxidation potential (IC50 = 28.7 ± 0.1 and 11.9 ± 0.2 µg/ml, respectively) and the lowest DPPH radical scavenging activity (467.7 µg/ml). Screening of the anticancer potential of all studied strains against four different human cancer cell lines (Caco-2, MCF-7, PC3, and HepG-2) demonstrated that Dolichospermum crassum HSSASE20 has the highest anticancer effect among all tested species against colon and prostate cancer cell lines (IC50 = 57.9 ± 0.4 and 44.1 ± 0.2 µg/ml, respectively), while Oscillatoria sancta HSSASE19 recorded the most anticancer effect against MCF-7 (breast cancer) cell line (IC50 = 15.1 ± 0.7 µg/ml). Dolichospermum spiroides HSSASE18 obtained the highest anticancer effect HepG-2 (hepatic cancer) cell line (IC50 = 48.8 ± 0.7 µg/ml). Additionally, cytotoxicity against healthy peripheral blood mononuclear cells was studied and revealed that Oscillatoria sancta was the safest one among all studied strains. Data obtained from the sensitivity index demonstrated that Dolichospermum crassum was the most sensitive strain against the four cancerous cell lines. Cyanobacteria and microalgae from the soil and drain water sources are efficient free radical scavengers, containing apoptogens capable of stimulating apoptotic cascades and overcoming chemo-resistance in cancer therapy. Thus, these novel secondary metabolites are an excellent alternative, safe, and low-cost antioxidant and anticancer therapeutic compounds.

Physiological and biochemical responses to aluminum-induced oxidative stress in two cyanobacterial species.

Phycoremediation technologies significantly contribute to solving serious problems induced by heavy metals accumulation in the aquatic systems. Here we studied the mechanisms underlying Al stress tolerance in two diazotrophic cyanobacterial species, to identify suitable species for Al phycoremediation. Al uptake as well as the physiological and biochemical responses of Anabaena laxa and Nostoc muscorum to 7 days Al exposure at two different concentrations i.e., mild (100 µM) and high dose (200 µM), were investigated. Our results revealed that A. laxa accumulated more Al, and it could acclimatize to long-term exposure of Al stress. Al induced a dose-dependent decrease in photosynthesis and its related parameters e.g., chlorophyll content (Chl a), phosphoenolpyruvate carboxylase (PEPC) and Ribulose‒1,5‒bisphosphate carboxylase/oxygenase (RuBisCo) activities. The affect was less pronounced in A. laxa than N. muscorum. Moreover, Al stress significantly increased cellular membrane damage as indicated by induced H2O2, lipid peroxidation, protein oxidation, and NADPH oxidase activity. However, these increases were lower in A. laxa compared to N. muscorum. To mitigate the impact of Al stress, A. laxa induced its antioxidant defense system by increasing polyphenols, flavonoids, tocopherols and glutathione levels as well as peroxidase (POX), catalase (CAT), glutathione reductase (GR) and glutathione peroxidase (GPX) enzymes activities. On the other hand, the antioxidant increases in N. muscorum were only limited to ascorbate (ASC) cycle. Overall, high biosorption/uptake capacity and efficient antioxidant defense system of A. laxa recommend its feasibility in the treatment of Al contaminated waters/soils.

Cyanobacterial removal by a red soil-based flocculant and its effect on zooplankton: an experiment with deep enclosures in a tropical reservoir in China.

As one kind of cheap, environmentally-friendly and efficient treatment materials for direct control of cyanobacterial blooms, modified clays have been widely concerned. The present study evaluated cyanobaterial removal by a red soil-based flocculant (RSBF) with a large enclosure experiment in a tropical mesotrophic reservoir, in which phytoplankton community was dominated by Microcystis spp. and Anabaena spp. The flocculant was composed of red soil, chitosan and FeCl3. Twelve enclosures were used in the experiment: three replicates for each of one control and three treatments RSBF15 (15 mg FeCl3 l-1), RSBF25 (25 mg FeCl3 l-1), and RSBF35 (35 mg FeCl3 l-1). The results showed that the red soil-based flocculant can significantly remove cyanobacterial biomass and reduce concentrations of nutrients including total nitrogen, nitrate, ammonia, total phosphorus, and orthophosphate. Biomass of Microcystis spp. and Anabaena spp. was reduced more efficiently (95%) than other filamentous cyanobacteria (50%). In the RSBF15 treatment, phytoplankton biomass recovered to the level of the control group after 12 days and cyanobacteria quickly dominated. Phytoplankton biomass in the RSBF25 treatment also recovered after 12 days, but green algae co-dominated with cyanobacteria. A much later recovery of phytoplankton until the day of 28 was observed under RSBF35 treatment, and cyanobacteria did no longer dominate the phytoplankton community. The application of red soil-based flocculant greatly reduces zooplankton, especially rotifers, however, Copepods and Cladocera recovered fast. Generally, the red soil-based flocculant can be effective for urgent treatments at local scales in cyanobacteria dominating systems.

Role of Ca2+ as protectant under heat stress by regulation of photosynthesis and membrane saturation in Anabaena PCC 7120.

The present study was aimed at understanding the effects of heat stress on selected physiological and biochemical parameters of a model cyanobacterium, Anabaena PCC 7120 in addition to amelioration strategy using exogenous Ca2+. A comparison of the cells exposed to heat stress (0-24 h) in the presence or absence of Ca2+ clearly showed reduction in colony-forming ability and increase in reactive oxygen species (ROS) leading to loss in the viability of cells of Ca2+-deficient cultures. There was higher level of saturation in membrane lipids of the cells supplemented with Ca2+ along with higher accumulation of proline. Similarly, higher quantum yield (7.8-fold) in Ca2+-supplemented cultures indicated role of Ca2+ in regulation of photosynthesis. Relative electron transport rate (rETR) decreased in both the sets with the difference in the rate of decrease (slow) in Ca2+-supplemented cultures. The Ca2+-supplemented sets also maintained high levels of open reaction centers of PS II in comparison to Ca2+-deprived cells. Increase in transcripts of both subunits ((rbcL and rbcS) of RubisCO from Ca2+-supplemented Anabaena cultures pointed out the role of Ca2+ in sustenance of photosynthesis of cells via CO2 fixation, thus, playing an important role in maintaining metabolic status of the heat-stressed cyanobacterium.

A new therapy prevents intellectual disability in mouse with phenylketonuria.

Untreated phenylketonuria (PKU) results in severe neurodevelopmental disorders, which can be partially prevented by an early and rigorous limitation of phenylalanine (Phe) intake. Enzyme substitution therapy with recombinant Anabaena variabilis Phe Ammonia Lyase (rAvPAL) proved to be effective in reducing blood Phe levels in preclinical and clinical studies of adults with PKU. Aims of present study were: a) to gather proofs of clinical efficacy of rAvPAL treatment in preventing neurological impairment in an early treated murine model of PKU; b) to test the advantages of an alternative delivering system for rAvPAL such as autologous erythrocytes. BTBR-Pahenu2-/- mice were treated from 15 to 64 post-natal days with weekly infusions of erythrocytes loaded with rAvPAL. Behavioral, neurochemical, and brain histological markers denoting untreated PKU were examined in early treated adult mice in comparison with untreated and wild type animals. rAvPAL therapy normalized blood and brain Phe; prevented cognitive developmental failure, brain depletion of serotonin, dendritic spine abnormalities, and myelin basic protein reduction. No adverse events or inactivating immune reaction were observed. In conclusion present study testifies the clinical efficacy of rAvPAL treatment in a preclinical model of PKU and the advantages of erythrocytes as carrier of the enzyme in term of frequency of the administrations and prevention of immunological reactions.

Biological activities and nitrogen and phosphorus removal during the anabaena flos-aquae biofilm growth using different nutrient form.

This work investigated the biological activities and nitrogen and phosphorus removal during the anabaena flos-aquae biofilm growth on the polyvinyl chloride (PVC) carriers, in different nutrient form mediums. The study showed that the production of dehydrogenase activity (DHA) and extracellular polymeric substances (EPS) can reach 40.4 g/(h·m2) and 115 × 10-2 g/m2 in an 11-day period, respectively, indicating that the anabaena flos-aquae biofilm had high biological activities. The results showed that the nitrogen and phosphorus removal reached 94.9 and 96.8%, respectively, in the ammonium form nitrogen group; while 97.7% of phosphorus were removed in the orthophosphate form phosphorous group. A comparison study was conducted and results showed that the present anabaena flos-aquae based biofilm provided a better removal of nitrogen and phosphorus than the other microalgae biofilms.

Screening of microalgae for integral biogas slurry nutrient removal and biogas upgrading by different microalgae cultivation technology.

The microalgae-based technology has been developed to reduce biogas slurry nutrients and upgrade biogas simultaneously. In this work, five microalgal strains named Chlorella vulgaris, Scenedesmus obliquus, Selenastrum capricornutum, Nitzschia palea, and Anabaena spiroides under mono- and co-cultivation were used for biogas upgrading. Optimum biogas slurry nutrient reduction could be achieved by co-cultivating microalgae (Chlorella vulgaris, Scenedesmus obliquus, and Nitzschia palea) with fungi using the pelletization technology. In addition, the effects of different ratio of mixed LED light wavelengths applying mixed light-emitting diode during algae strains and fungi co-cultivation on CO2 and biogas slurry nutrient removal efficiency were also investigated. The results showed that the COD (chemical oxygen demand), TN (total nitrogen), and TP (total phosphorus) removal efficiency were 85.82 ± 5.37%, 83.31 ± 4.72%, and 84.26 ± 5.58%, respectively at red: blue = 5:5 under the co-cultivation of S. obliquus and fungi. In terms of biogas upgrading, CH4 contents were higher than 90% (v/v) for all strains, except the co-cultivation with S. obliquus and fungi at red: blue = 3:7. The results indicated that co-cultivation of microalgae with fungi under mixed light wavelengths treatments was most successful in nutrient removal from wastewater and biogas upgrading.

New thermodynamic entropy calculation based approach towards quantifying the impact of eutrophication on water environment.

Although the eutrophication phenomenon has been studied for a long time, there are still no quantifiable parameters available for a comprehensive assessment of its impacts on the water environment. As contamination alters the thermodynamic equilibrium of a water system to a state of imbalance, a novel method was proposed, in this study, for its quantitative evaluation. Based on thermodynamic analyses of the algal growth process, the proposed method targeted, both theoretically and experimentally, the typical algae species encountered in the water environment. By calculating the molar enthalpy of algae biomass production, the heat energy dissipated in the photosynthetic process was firstly evaluated. The associated entropy production (ΔS) in the aquatic system could be then obtained. For six algae strains of distinct molecular formulae, the heat energy consumed for the production of a unit algal biomass was found to proportionate to the mass of nitrogen (N) or phosphorus (P) uptake through photosynthesis. A proportionality relationship between ΔS and the algal biomass with a coefficient circa 44kJ/g was obtained. By the principle of energy conservation, the heat energy consumed in the process of algae biomass production is stored in the algal biomass. Furthermore, by measuring the heat of combustion of mature algae of Microcystis flos-aquae, Anabaena flos-aquae, and Chlorella vulgaris, the proportionality relationships between the heat energy and the N and P contents were validated experimentally at 90% and 85% confidence levels, respectively. As the discharge of excess N and P from domestic wastewater treatment plants is usually the main cause of eutrophication, the proposed impact assessment approach estimates that for a receiving water body, the ΔS due to a unit mass of N and P discharge is 268.9kJ/K and 1870.1kJ/K, respectively. Consequently, P discharge control would be more important for environmental water protection.

Proteomic analysis reveals contrasting stress response to uranium in two nitrogen-fixing Anabaena strains, differentially tolerant to uranium.

Two strains of the nitrogen-fixing cyanobacterium Anabaena, native to Indian paddy fields, displayed differential sensitivity to exposure to uranyl carbonate at neutral pH. Anabaena sp. strain PCC 7120 and Anabaena sp. strain L-31 displayed 50% reduction in survival (LD50 dose), following 3h exposure to 75µM and 200µM uranyl carbonate, respectively. Uranium responsive proteome alterations were visualized by 2D gel electrophoresis, followed by protein identification by MALDI-ToF mass spectrometry. The two strains displayed significant differences in levels of proteins associated with photosynthesis, carbon metabolism, and oxidative stress alleviation, commensurate with their uranium tolerance. Higher uranium tolerance of Anabaena sp. strain L-31 could be attributed to sustained photosynthesis and carbon metabolism and superior oxidative stress defense, as compared to the uranium sensitive Anabaena sp. strain PCC 7120. SIGNIFICANCE: Uranium responsive proteome modulations in two nitrogen-fixing strains of Anabaena, native to Indian paddy fields, revealed that rapid adaptation to better oxidative stress management, and maintenance of metabolic and energy homeostasis underlies superior uranium tolerance of Anabaena sp. strain L-31 compared to Anabaena sp. strain PCC 7120.

Differential regulation of ssb genes in the nitrogen-fixing cyanobacterium, Anabaena sp. strain PCC71201.

Anabaena sp. PCC7120 possesses three genes coding for single-stranded DNA-binding (SSB) protein, of which ssb1 was a single gene, and ssb2 and ssb3 are the first genes of their corresponding operons. Regulation of the truncated ssb genes, ssb1 (alr0088) and ssb2 (alr7559), was unaffected by N-status of growth. They were negatively regulated by the SOS-response regulatory protein LexA, as indicated by the (i) binding of Anabaena LexA to the LexA box of regulatory regions of ssb1 and ssb2, and (ii) decreased expression of the downstream gfp reporter gene in Escherichia coli upon co-expression of LexA. However, the full-length ssb gene, ssb3 (all4779), was regulated by the availability of Fe2+ and combined nitrogen, as indicated by (i) increase in the levels of SSB3 protein on Fe2+ -depletion and decrease under Fe2+ -excess conditions, and (ii) 1.5- to 1.6-fold decrease in activity under nitrogen-fixing conditions compared to nitrogen-supplemented conditions. The requirement of Fe2+ as a co-factor for repression by FurA and the increase in levels of FurA under nitrogen-deficient conditions in Anabaena (Lopez-Gomollon et al. 2007) indicated a possible regulation of ssb3 by FurA. This was substantiated by (i) the binding of FurA to the regulatory region of ssb3, (ii) repression of the expression of the downstream gfp reporter gene in E. coli upon co-expression of FurA, and (iii) negative regulation of ssb3 promoter activity by the upstream AT-rich region in Anabaena. This is the first report on possible role of FurA, an important protein for iron homeostasis, in DNA repair of cyanobacteria.

Profenofos induced modulation in physiological indices, genomic template stability and protein banding patterns of Anabaena sp. PCC 7120.

To understand the mechanism underlying organophosphate pesticide toxicity, cyanobacterium Anabaena PCC 7120 was subjected to varied concentrations (0, 5, 10, 20 and 30 mg L(-1)) of profenofos and the effects were investigated in terms of changes in cellular physiology, genomic template stability and protein expression pattern. The supplementation of profenofos reduced the growth, total pigment content and photosynthetic efficiency of the test organism in a dose dependent manner with maximum toxic effect at 30 mg L(-1). The high fluorescence intensity of 2', 7' -dichlorofluorescin diacetate and increased production of malondialdehyde confirmed the prevalence of acute oxidative stress condition inside the cells of the cyanobacterium. Rapid amplified polymorphic DNA (RAPD) fingerprinting and SDS-PAGE analyses showed a significant alteration in the banding patterns of DNA and proteins respectively. A marked increase in superoxide dismutase, catalase, peroxidase activity and a concomitant reduction in glutathione content indicated their possible role in supporting the growth of Anabaena 7120 up to 20 mg L(-1). These findings suggest that the uncontrolled use of profenofos in the agricultural fields may not only lead to the destruction of the cyanobacterial population, but it would also disturb the nutrient dynamics and energy flow.

Role of calcium in the mitigation of heat stress in the cyanobacterium Anabaena PCC 7120.

The effects of exogenously added CaCl2 (0.25mM) on photopigments, photosynthetic O2-evolution, antioxidative enzyme activity, membrane damage, expression of two heat shock genes (groEL and groES) and apoptotic features in Anabaena 7120 under heat stress (45°C) for up to 24h were investigated. Heat stress lowered the level of photopigments; however, Ca2+--supplemented cultures showed a low level reduction in Chl a but induced accumulation of carotenoids and phycocyanin under heat stress. Photosynthetic O2-evolving capacity was maintained at a higher level in cells from Ca2+-supplemented medium. Among the antioxidative enzymes, superoxide dismutase activity was unaffected by the presence or absence of Ca2+ in contrast to increases in catalase, ascorbate peroxidase and glutathione reductase activities in cells grown in Ca2+-supplemented medium. Lower levels of lipid peroxidation were recorded in Anabaena cells grown in Ca2+-supplemented medium in comparison to cells from Ca2+--deprived medium. Target cells grown in Ca2+-deprived medium developed apoptotic features in the early stages of heat shock, while Ca2+ application seemed to interfere with apoptosis because only a few cells showed such features after 24 h of heat exposure, indicating a role for Ca2+ in maintaining cell viability under heat stress. There was also continuous up regulation of two important heat shock genes (groEL and groES) in Ca2+-supplemented cultures, exposed to heat shock, again indicating a role for Ca2+ in stress management.

Phosphorus removal coupled to bioenergy production by three cyanobacterial isolates in a biofilm dynamic growth system.

In the present study a closed incubator, designed for biofilm growth on artificial substrata, was used to grow three isolates of biofilm-forming heterocytous cyanobacteria using an artificial wastewater secondary effluent as the culture medium. We evaluated biofilm efficiency in removing phosphorus, by simulating biofilm-based tertiary wastewater treatment and coupled this process with biodiesel production from the developed biomass. The three strains were able to grow in the synthetic medium and remove phosphorus in percentages, between 6 and 43%, which varied between strains and also among each strain according to the biofilm growth phase. Calothrix sp. biofilm turned out to be a good candidate for tertiary treatment, showing phosphorus reducing capacity (during the exponential biofilm growth) at the regulatory level for the treated effluent water being discharged into natural water systems. Besides phosphorus removal, the three cyanobacterial biofilms produced high quality lipids, whose profile showed promising chemical stability and combustion behavior. Further integration of the proposed processes could include the integration of oil extracted from these cyanobacterial biofilms with microalgal oil known for high monounsaturated fatty acids content, in order to enhance biodiesel cold flow characteristics.

Unraveling of cross talk between Ca(2+) and ROS regulating enzymes in Anabaena 7120 and ntcA mutant.

In order to understand a cross talk between Ca(2+) and ROS regulating enzymes and the possible involvement of ntcA gene, Anabaena sp. PCC 7120 and its derivative ntcA mutant grown in varied levels of calcium chloride (0, 1, 10, and 100 mM) have been investigated. Scanning Electron Microscopy showed abnormal structure formation at high calcium concentration (100 mM) both in wild type and mutant. Fv /Fm values suggested that 100 mM calcium concentration was detrimental for photosynthetic apparatus. SOD, catalase, APX, GR, and peroxidase activity were found to be maximum for 100 mM and minimum for 1 mM of exogenously supplied calcium salt. NADPH contents were higher for wild type than mutant. RAPD-PCR and SDS-PAGE analysis revealed a difference in DNA as well as proteome pattern with changes in calcium chloride regime. Prominent bands of approximately 70, 33, 21, and 14 kDa expressed in the wild type served as the marker polypeptide bands under calcium supplementation. Results suggest that higher levels of calcium ion disturb the cellular homeostasis generating ROS, thereby inducing enhanced levels of antioxidative enzymes. Further, data also suggests possible involvement of ntcA gene in cross talk between calcium ion and ROS regulating enzymes.