Balkrishna Tiwari

Regulation of organophosphate metabolism in cyanobacteria. A review

Cyanobacteria sense the environmental phosphate level and respond accordingly with the help of a two component regulatory system SphS-SphR orthologous to PhoR-PhoB of E. coli, where SphS act as a sensor kinase and SphR as a response regulator. Under phosphate limiting condition SphS-SphR regulates the expression of many genes including genes which do not have the direct role in metabolism and transport of phosphate. Thus there is some crosstalk mechanism which connects this regulatory system to the other metabolic processes. Different types of enzymes and transporters are expressed by cyanobacteria under phosphate limitation to release and transport the phosphate from different organic compounds present in the environment. Genes encoding these enzymes and transporters contain Pho boxes in their promoter region where SphR binds and regulate their expression under phosphate limitation. The machinery and mechanism of regulation is not uniform in cyanobacteria as it varies in different groups according to their evolutionary adaptations. This review article is summarizing the reports on machinery and mechanism of organophosphate metabolism in cyanobacteria.

Ferric Uptake Regulator (FUR) protein: properties and implications in cyanobacteria

The Ferric uptake regulator (Fur) protein is a global iron regulator found in most prokaryotes. Although the Fur protein is involved in a variety of metabolic pathways, it is specifically known for the regulation of several iron responsive genes. It binds to the highly conserved sequences located in the upstream promoter region known as iron boxes, using ferrous ion as a co-repressor. Apart from that, the Fur protein is also directly/indirectly involved in a variety of other crucial physiological pathways. Hence, understanding the mechanism of action and the mechanistic pathways of iron regulation by Fur is necessary and important. The basic understanding of the functioning and properties of Fur protein along with its role, interaction and regulation at various levels in cyanobacteria has been discussed in detail.

Modulation of fatty acids and hydrocarbons in Anabaena 7120 and its ntcA mutant under calcium

Calcium being a signaling molecule and mediator of cell response, we examined the modulation in fatty acid and hydrocarbon profiles of wild type cyanobacterium Anabaena sp. PCC 7120 and its ntcA mutant under the influence of different calcium chloride concentrations (0–10 mM). Dynamic modifications in fatty acid and hydrocarbon profile were evident through GC‐FID analysis of extracted lipids. In the wild type, increase in CaCl2 (10 mM) resulted in unsaturation of fatty acids (observed in terms of high MUFA/PUFA ratio) while hydrocarbon production was distinctly high in the mutant strain compared to wild type at all tested concentrations. The synthesis of short chain hydrocarbons (C5–C8) were dominated at inhibitory concentration (10 mM CaCl2) in mutant strain. Results suggest that the increase in MUFA/PUFA ratio at inhibitory concentration in wild type, and higher percentage of hydrocarbons in mutant strain, may be attributed to the survival and acclimation strategies under altered calcium environment. Our results also suggest the involvement of the ntcA gene (master regulator of N2 metabolism) in regulation of carbon metabolism; specifically fatty acid, hydrocarbon, and other metabolic compounds essential for maintenance and sustenance of growth under stress condition. Thus, our study outlines basic acclimation response along with possibilities of production of fatty acid and hydrocarbon derived biofuel and other bioactive compounds in Anabaena sp. PCC 7120 under altered calcium levels which could be of biotechnological interest.

Transcriptional regulation of acetyl CoA and lipid synthesis by PII protein in Synechococcus PCC 7942

PII protein family is widespread in prokaryotes and plants. In this study, impacts of PII deficiency on the synthesis of acetyl CoA and acetyl CoA carboxylase enzyme (ACCase) was analyzed in the Synechococcus sp. PCC 7942 by evaluating the mRNA levels of pyruvate kinase (PK), pyruvate dehydrogenase (PDH), citrate synthase (CS), biotin synthase (BS), biotin carboxylase (BC), biotin carboxyl carrier protein (BCCP), carboxyl transferase (CT) α and β subunits. The PII deficient Synechococcus sp. PCC 7942 showed upregulation of all the above‐mentioned genes, except CS. Analyses of genes required for acetyl coA synthesis exhibited a substantial increase in the transcript levels of PK and PDH in the PII mutant strain. In addition, the PII mutant also displayed reduced acetyl CoA content, high ACCase activity, and increased lipid content. The lessening of acetyl CoA content was attributed to the rapid utilization of acetyl CoA in fatty acid synthesis as well as in the TCA cycle whereas the increased ACCase activity was ascribed to the rise in mRNA levels of BS, BC, BCCP, CT α, and β genes. However, increased lipid content was correlated with the declined total protein content. Hence, the study suggested that PII protein regulates the synthesis of acetyl CoA and ACCase enzyme at the transcriptional level.

Sequential role of biosorption and biodegradation in rapid removal degradation and utilization of methyl parathion as a phosphate source by a new cyanobacterial isolate Scytonema sp. BHUS-5

ABSTRACT A new isolate of genus Scytonema distinct from its closest relative cyanobacterium, Scytonema hofmanni was found efficient in the removal and degradation of organophosphorus (OP) pesticide, methyl parathion (MP). The cyanobacterial isolate was also capable of utilizing the phosphorus present in the MP following its degradation, which was evident from the increase in growth (chlorophyll content), biomass, protein content, and total phosphorus in comparison to cyanobacterium grown in phosphate-deficient cultures. The rapid removal of MP by the cyanobacterium during initial 6 hours of incubation was defined by the pseudo-second-order biosorption kinetics model, which indicated the involvement of chemosorption in initial removal of pesticide. Further, degradation of MP was also confirmed by the appearance of p-nitrophenol in the medium after 24 hours of incubation. Thus, the cyanobacterial isolate of Scytonema sp. BHUS-5 seems to be a potential bioremediation agent for the removal of OP pesticide, MP from the habitat.

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

Abstract 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.

Antimicrobial Compounds From Actinobacteria

Abstract Actinobacteria, bearing the characteristics of both bacteria and fungus, are considered as one of the most medicinally important candidates because of their tremendous ability to produce various bioactive compounds. Members of actinobacteria are strictly gram positive in nature and represent the most efficient group of prokaryotes capable of producing novel metabolites. The metabolites produced by actinobacteria exhibit inhibitory effects against different pathogens such as MDR bacterial strains, fungi, viruses, protozoa, and other parasites. Numerous antimicrobial compounds such as beta-lactams, tetracyclines, phenazine, aminoglycosides, etc. have already been isolated and characterized from several actinobacteria and are used as drugs to control diverse human diseases. Two individual pathways, i.e., nonribosomal peptide synthetase (NRPS) and polyketide synthase (PKS I and II), are thought to be responsible for the synthesis of these compounds in actinobacteria. This review demonstrates the diversity, chemistry, and bioactivity of actinobacterial metabolites along with the biochemical and genetic basis of their production.