Browsing by Author "Keshwanand Tripathi"

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On agricultural importance of cyanobacteria mediated phosphate availability in soil
(Nova Science Publishers, Inc., 2015) Keshwanand Tripathi; Ashwani K. Rai; Naveen K. Sharma
Life on earth is dependent on phosphorous (P). In many natural ecosystems, P is one of the principle macronutrients limiting the growth and development of living forms. Diminishing global pool, escalating cost and limited supply have made P a geostrategically important mineral. In many agro-ecosystems, contrary to the common belief P is available in plenty but in forms that cannot be utilized directly by the crop plants. The limited availability of P to the crops is a serious threat to the global food security. In tropical regions, cyanobacteria is an agronomically important group of prokaryotic photoautotrophs often constitute a dominant microflora in agro-ecosystems such as paddy and sugarcane-fields. They are bestowed with efficient systems to sense in milieu phosphate deficiency. Moreover, they have developed different strategies to scavenge organic phosphate available in the external medium into usable inorganic forms. Apart from fulfilling their own need, the freed inorganic P becomes available to the crop plants. In this chapter, we have reviewed various strategies adopted by cyanobacteria to meet out their phosphate need under Pi-deficient conditions; and agricultural significance of cyanobacteria-mediated Pi enrichment of soil in increasing crop productivity. © 2015 by Nova Science Publishers, Inc. All rights reserved.
Physiological, biochemical and molecular responses of the halophilic cyanobacterium Aphanothece halophytica to Pi-deficiency
(2013) Keshwanand Tripathi; Naveen Kumar Sharma; Hakuto Kageyama; Teruhiro Takabe; Ashwani Kumar Rai
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. © 2013 © British Phycological Society.
Sustainability and cyanobacteria (blue-green algae): Facts and challenges
(2011) Naveen K. Sharma; Sri Prakash Tiwari; Keshwanand Tripathi; Ashwani K. Rai
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. © 2010 Springer Science+Business Media B.V.