Physiological adaptations and tolerance towards higher concentration of selenite (Se+4) in Enterobacter sp. AR-4, Bacillus sp. AR-6 and Delftia tsuruhatensis AR-7 |
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Authors: | Dhan Prakash Janmejay Pandey B N Tiwary Rakesh K Jain |
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Institution: | (1) Institute of Microbial Technology (CSIR), Sector 39-A, Chandigarh, 160 036, India;(2) School of Biotechnology, Guru Ghasidas University, Bilaspur, 495 009, India; |
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Abstract: | Environmental contamination with selenium is a major health concern. A few bacterial strains have been isolated that can transform
toxic selenite to non-toxic elemental selenium only at low concentrations (0.001–150 mM) in recent past. We have previously
reported isolation and characterization of few selenite-tolerant bacterial strains. These strains were found to be resistant
to selenite at (300–600 mM) concentrations. In the present study we have characterized some physiological adaptations of strains
Enterobacter sp. AR-4, Bacillus sp. AR-6 and Delftia tsuruhatensis AR-7 during exposure to higher concentration of selenite under aerobic and anaerobic environments. Adaptive responses are
largely associated with alteration of cell morphology and change in total cellular fatty acid composition. Interestingly,
electron microscopy studies revealed substantial decrease in cell size and intracellular deposition of Se0 crystals when reduction is carried out under aerobic conditions. On the other hand, cell size increased with adhesion of
Se0 on cell surface during anaerobic reduction. Fatty acid composition analysis demonstrated selective increase in saturated
and cyclic fatty acids and decrease in unsaturated ones during aerobic transformation. Changes observed during anaerobic transformation
were in surprising contrast as indicated by total absence of saturated and cyclic fatty acids. Results presented here provide
evidences for putative occurrence of two distinct mechanisms involved in tolerance towards higher concentrations of selenite
utilization under aerobic and anaerobic conditions. Further, prior exposure to higher concentration of Se+4 enabled rapid adaptation indicating role of inducible system in adaptation. |
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