• Bhakti Basu

      Articles written in Journal of Biosciences

    • The Kdp-ATPase system and its regulation

      Anand Ballal Bhakti Basu Shree Kumar Apte

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      K+, the dominant intracellular cation, is required for various physiological processes like turgor homeostasis, pH regulation etc. Bacterial cells have evolved many diverse K+ transporters to maintain the desired concentration of internal K+. In E. coli, the KdpATPase (comprising of the KdpFABC complex), encoded by the kdpFABC operon, is an inducible high-affinity K+ transporter that is synthesised under conditions of severe K+ limitation or osmotic upshift. The E. coli kdp expression is transcriptionally regulated by the KdpD and KdpE proteins, which together constitute a typical bacterial two-component signal transduction system. The Kdp system is widely dispersed among the different classes of bacteria including the cyanobacteria. The ordering of the kdpA, kdpB and kdpC is relatively fixed but the kdpD/E genes show different arrangements in distantly related bacteria. Our studies have shown that the cyanobacterium Anabaena sp. strain L-31 possesses two kdp operons, kdp1 and kdp2, of which, the later is expressed under K+ deficiency and desiccation. Among the regulatory genes, the kdpD ORF of Anabaena L-31 is truncated when compared to the kdpD of other bacteria, while a kdpE-like gene is absent. The extremely radio-resistant bacterium, Deinococcus radiodurans strain R1, also shows the presence of a naturally short kdpD ORF similar to Anabaena in its kdp operon. The review elaborates the expression of bacterial kdp operons in response to various environmental stress conditions, with special emphasis on Anabaena. The possible mechanism(s) of regulation of the unique kdp operons from Anabaena and Deinococcus are also discussed.

    • In situ real-time evaluation of radiation-responsive promoters in the extremely radioresistant microbe Deinococcus radiodurans

      Narasimha Anaganti Bhakti Basu Shree Kumar Apte

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      A third generation promoter probe shuttle vector pKG was constructed, using the green fluorescent protein as a reporter, for in situ evaluation of Deinococcal promoter activity in Escherichia coli or Deinococcus radiodurans. The construct yielded zero background fluorescence in both the organisms, in the absence of promoter sequences. Fifteen deinococcal promoters, either harbouring Radiation and Desiccation Response Motif (RDRM) or not, were cloned in vector pKG. Only the RDRM-promoter constructs displayed (i) gamma radiation inducible GFP expression in D. radiodurans, following gamma irradiation, (ii) DdrO-mediated repression of GFP expression in heterologous E. coli, or (iii) abolition in GFP induction following gamma irradiation, in pprI mutant of D. radiodurans. Utility of pKG vector for real-time in situ assessment of deinococcal promoter function was, thus, successfully demonstrated.

    • New insights into the activation of Radiation Desiccation Response regulon in Deinococcus radiodurans


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      The highly radiation-resistant bacterium Deinococcus radiodurans responds to gamma radiation or desiccationthrough the coordinated expression of genes belonging to Radiation and Desiccation Resistance/Response(RDR) regulon. RDR regulon is operated through cis-acting sequence RDRM (Radiation DesiccationResponse Motif), trans-acting repressor DdrO and protease IrrE (also called PprI). The present study evaluatedwhether RDR regulon controls the response of D. radiodurans to various other DNA damaging stressors, towhich it is resistant, such as UV rays, mitomycin C (MMC), methyl methanesulfonate (MMS), ethidiumbromide (EtBr), etc. Activation of 3 RDR regulon genes (ddrB, gyrB and DR1143) was studied by taggingtheir promoter sequences with a highly sensitive GFP reporter. Here we demonstrated that all the DNAdamaging stressors elicited activation of RDR regulon of D. radiodurans in a dose-dependent and RDRM-/IrrE-dependent manner. However, ROS-mediated indirect effects [induced by hydrogen peroxide (H2O2),methyl viologen (MV), heavy metal/metalloid (zinc or tellurite), etc.] did not activate RDR regulon. We alsoshowed that level of activation was inversely proportional to cellular abundance of repressor DdrO. Our datastrongly suggests that direct DNA damage activates RDR regulon in D. radiodurans.

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