Naveen K. Sharma

Sustainability and cyanobacteria (blue-green algae): facts and challenges

Cyanobacteria (blue-green algae) are widely distributed Gram-negative oxygenic photosynthetic prokaryotes with a long evolutionary history. They have potential applications such as nutrition (food supplements and fine chemicals), in agriculture (as biofertilizer and in reclamation of saline USAR soils) and in wastewater treatment (production of exopolysaccharides and flocculants). In addition, they also produce wide variety of chemicals not needed for their normal growth (secondary metabolites) which show powerful biological activities such as strong antiviral, antibacterial, antifungal, antimalarial, antitumoral and anti-inflammatory activities useful for therapeutic purposes. In recent years, cyanobacteria have gained interest for producing biofuels (both biomass and H2 production). Because of their simple growth needs, it is potentially cost-effective to exploit cyanobacteria for the production of recombinant compounds of medicinal and commercial value. Recent advances in culture, screening and genetic engineering techniques have opened new ways to exploit the potential of cyanobacteria. This review analyses the sustainability of cyanobacteria to solve global problems such as food, energy and environmental degradation. It emphasizes the need to adopt multidisciplinary approaches and a multi-product production (biorefinery) strategy to harness the maximum benefit of cyanobacteria.

Phosphate Metabolism in the Cyanobacterium Anabaena doliolum Under Salt Stress

In the present study, we have investigated the effects of NaCl concentrations on the growth and phosphate metabolism of an Anabaena doliolum strain isolated from a paddy field, in order to determine the possible effects of salinization. Growth rate, chlorophyll content, and protein content decreased with increasing salt concentration in the growth medium, while carbohydrate concentration increased. Phosphate content and phosphate uptake rate decreased. There was an increase in total alkaline phosphatase activity, with an approximately 7-fold increase in extracellular activity compensating for an approximately 3-fold decrease in cell-bound activity. NaCl effects on protein and chlorophyll concentrations were greater in P-deficient medium, while presence or absence of P in the medium had little effect on cellular carbohydrate concentrations. It is concluded that growth in high salt likely leads to reduced phosphate uptake in A. doliolum.

Microcystin producing cyanobacterium Nostoc sp. BHU001 from a pond in India.

The cyanobacterium Nostoc sp. BHU001 is a new isolate from a pond in India. The cyanobacterium produces more than ten peptides including five microcystin (MC) variants, MC-LR, -WR, -AR, -LA and methylated MC-LR, and a new peptide similar to cyanopeptolin. Total MC content determined by ELISA was 25.2 microg g(-1) dry wt of the cyanobacterium, dominated by MC-LR (54%). This is the first report of MC producing Nostoc strain from India.

Microbial Interactions in the Arsenic Cycle: Adoptive Strategies and Applications in Environmental Management

Arsenic (As) is a nonessential element that is often present in plants and in other organisms. However, it is one of the most hazardous of toxic elements globally. In many parts of the world, arsenic contamination in groundwater is a serious and continuing threat to human health. Microbes play an important role in regulating the environmental fate of arsenic. Different microbial processes influence the biogeochemical cycling of arsenic in ways that affect the accumulation of different arsenic species in various ecosystem compartments. For example, in soil, there are bacteria that methylate arsenite to trimethylarsine gas, thereby releasing arsenic to the atmosphere.In marine ecosystems, microbes exist that can convert inorganic arsenicals to organic arsenicals (e.g., di- and tri-methylated arsenic derivatives, arsenocholine,arsenobetaine, arsenosugars, arsenolipids). The organo arsenicals are further metabolized to complete the arsenic cycle.Microbes have developed various strategies that enable them to tolerate arsenic and to survive in arsenic-rich environments. Such strategies include As exclusion from cells by establishing permeability barrier, intra- and extracellular sequestration,active efflux pumps, enzymatic reduction, and reduction in the sensitivity of cellular targets. These strategies are used either singly or in combination. In bacteria,the genes for arsenic resistance/detoxification are encoded by the arsenic resistance operons (ars operon).In this review, we have addressed and emphasized the impact of different microbial processes (e.g., arsenite oxidation, cytoplasmic arsenate reduction, respiratory arsenate reduction, arsenite methylation) on the arsenic cycle. Microbes are the only life forms reported to exist in heavy arsenic-contaminated environments. Therefore,an understanding of the strategies adopted by microbes to cope with arsenic stress is important in managing such arsenic-contaminated sites. Further future insights into the different microbial genes/proteins that are involved in arsenic resistance may also be useful for developing arsenic resistant crop plants.

The freshwater cyanobacterium Anabaena doliolum transformed with ApGSMT-DMT exhibited enhanced salt tolerance and protection to nitrogenase activity, but became halophilic

Glycine betaine (GB) is an important osmolyte synthesized in response to different abiotic stresses, including salinity. The two known pathways of GB synthesis involve: 1) two step oxidation of choline (choline → betaine aldehyde → GB), generally found in plants, microbes and animals; and 2) three step methylation of glycine (glycine → sarcosine → dimethylglycine → GB), mainly found in halophilic archaea, sulphur bacteria and the cyanobacterium Aphanothece (Ap.) halophytica. Here, we transformed a salt-sensitive freshwater diazotrophic filamentous cyanobacterium Anabaena (An.) doliolum with N-methyltransferase genes (ApGSMT-DMT) from Ap. halophytica using the triparental conjugation method. The transformed An. doliolum synthesized and accumulated GB in cells, and showed increased salt tolerance and protection to nitrogenase activity. The salt responsiveness of the transformant was also apparent as GB synthesis increased with increasing concentrations of NaCl in the nutrient solution, and maximal [12.92 µmol (g dry weight)(-1)] in cells growing at 0.5 M NaCl. Therefore, the transformed cyanobacterium has changed its behaviour from preferring freshwater to halophily. This study may have important biotechnological implications for the development of stress tolerant nitrogen-fixing cyanobacteria as biofertilizers for sustainable agriculture.

Physiological, biochemical and molecular responses of the halophilic cyanobacterium Aphanothece halophytica to Pi-deficiency

We studied the responses of a halophilic cyanobacterium Aphanothece halophytica at surplus (normal composition of growth medium containing 125 µM PO43−), sufficient (the minimum concentration supporting optimal growth, 22 µM PO43−) and deficient (no external supply of Pi) concentrations of inorganic phosphate (Pi). The cyanobacterium was able to grow well in Pi-deficient conditions until the end of incubation (14 days), though at a marginally reduced rate. The cellular P-quota in Pi-surplus cells at the end of incubation was 2.7 times that of their initial P-quota (0.75 µmol mg protein−1), and remained fairly high (0.442 µmol mg protein−1) even in Pi-deficient medium. However, cultures growing in Pi-sufficient medium (22 µM PO43−), upon transfer to Pi-deficient medium, exhibited a rapid decline in cellular P level. Furthermore, cells growing in Pi-surplus medium showed a rapid efflux of P into the external medium. Aphanothece halophytica exhibited a biphasic phosphate transport system involving both high- (Ks 2.06 µM) and low-affinity (Ks 17.85 µM) transporters. Cyanobacterial cells maintained a basal level (constitutively expressed and not affected by Pi availability) of alkaline phosphatase (APase) activity, which increased 5–7-fold under Pi-deficiency. Supplementation of phosphate to the medium caused gradual decline in the enzyme activity to the basal level. Pi-deficient cells showed an enhanced level of transcripts for PPi-dependent glycolytic enzymes. Though moderate, Pi-deficiency affected the respiration, photosynthetic rate and electron transport chain activity negatively. PS II activity was most sensitive to Pi-deficiency, followed by PSI and whole chain. Pi-replete A. halophytica cells showed a single high-affinity nitrate transport system. However, deficiency of Pi reduced the nitrate and nitrite reductase activities.

From natural to human-impacted ecosystems: rationale to investigate the impact of urbanization on cyanobacterial diversity in soils

Human activities have long been recognized as a major force shaping the biosphere. Advancing urbanization is one such transformation with unforeseen effect on the soil microbiota, including the cyanobacteria. This includes the loss of agronomically important nitrogen fixing cyanobacteria, which may negatively affect the agricultural productivity of peri-urban soils. However, empirical studies are lacking to validate the statement. Even, in journals specifically dealing with diversity and distribution of organisms, urban ecology and ecosystems. Here, I describe a critical area beset with challenges that needs to be investigated.

Algal Particles in the Atmosphere

Because of various natural processes and anthropocentric activities atmosphere remain constantly loaded with diverse kinds of biological particles. Although, their nature, prevalence and distribution varying in space and time. A total of 353 morphologically distinct airborne algal taxa have been identified from the atmosphere of various parts of the globe. The composition of aero-algal communities exhibits seasonal variation, and is strongly influenced often by a combination of various climatic factors. Here, we have reviewed the ecological and economic significances of airborne microalgal particles. Including the methodological (metagenomic approach) and technological (cutting-edge molecular techniques) advances that are being used to characterize the aeroalgal communities.