Paper Title
Strain Improvement of Selected Bacteria using Physical Mutagen for Bioremediation of Hexavalent Chromium: A Comparative Study

Abstract
Bioremediation using microbes is eco-friendly and economical. There is an increased demand for improvised strain of microbes for chromium removal from effluents. Strain improvement using mutagens are promising for generation of strains with better chromium removal efficiency. The present work aims at improvising the bacterial strainsBacillus subtilis, Bacillus amyloliquifaciensand Micrococcus luteus (isolated from an indigenous source of electroplating effluent of an industry in Peenya, Bangalore)by inducing random physical mutations with ultraviolet light and studying its impact on chromium remediation capacity. The study also reveals the effect of chromium on growth of microbes. UV survival curve was plotted and mutants with more than 50 % survival rate, were chosen for remediation studies. Wild type and mutants were assessed for chromium removal efficiency using diphenylcarbazide method. Bacillus amyloliquifaciens exposed to UV radiation for 80 minutesshowed 100 % chromium removal efficiency in 8 hours, while the wild type remediated in 10 hours. Bacillus subtilis that was exposed for 120 min showed 100 % removal efficiency in 17 hours, while the wild type remediated 96 % of chromium in 19 hours. Both wild type and mutants of Micrococcus luteusremoved 96 % chromium in 18 hours. This study indicates the successful strain improvement of Bacillus subtilis and Bacillus amyloliquifaciens in generating mutant with a better ability for chromium removal, while Micrococcus luteus being resistant to UV irradiation failed to show any improvement in removal efficiency of chromium. Keywords - Chromium, Microbial remediation, Strain improvement, Bacillus amyloliquifaciens, Bacillussubtilis, Micrococcus luteus, Ultraviolet light.