Bioremoval of hexavalent chromium from water by a salt tolerant bacterium, Exiguobacterium sp. GS1

Pollution of terrestrial surfaces and aquatic systems by hexavalent chromium, Cr(VI), is a worldwide public health problem. A chromium resistant bacterial isolate identified as Exiguobacterium sp. GS1 by 16S rRNA gene sequencing displayed high rate of removal of Cr(VI) from water. Exiguobacterium sp. GS1 is 99% identical to Exiguobacterium acetylicum. The isolate significantly removed Cr(VI) at both high and low concentrations (1-200 microg mL(-1)) within 12 h. The Michaelis-Menten K ( m ) and V (max) for Cr(VI) bioremoval were calculated to be 141.92 microg mL(-1) and 13.22 microg mL(-1) h(-1), respectively. Growth of Exiguobacterium sp. GS1 was indifferent at 1-75 microg mL(-1) Cr(VI) in 12 h. At initial concentration of 8,000 microg L(-1), Exiguobacterium sp. GS1 displayed rapid bioremoval of Cr(VI) with over 50% bioremoval in 3 h and 91% bioremoval in 8 h. Kinetic analysis of Cr(VI) bioremoval rate revealed zero-order in 8 h. Exiguobacterium sp. GS1 grew and significantly reduced Cr(VI) in cultures containing 1-9% salt indicating high salt tolerance. Similarly the isolate substantially reduced Cr(VI) over a wide range of temperature (18-45 degrees C) and initial pH (6.0-9.0). The T (opt) and initial pH(opt) were 35-40 degrees C and 7-8, respectively. Exiguobacterium sp. GS1 displayed a great potential for bioremediation of Cr(VI) in diverse complex environments.