Hexavalent chromium reduction by whole cells and cell free extract of the moderate halophilic bacterial strain Halomonas sp. TA-04

The current study was aimed to characterize a bacterial strain isolated from Cr(VI)-polluted sediments for its role in Cr(VI)-reduction as whole cell and by cell free extract. A new moderately halophilic Cr (VI)-resistant bacterial strain TA-04 was isolated from polluted marine sediments near a stainless steel plant in Southern Italy, 16S rRNA analysis placed the isolate close to the species Halomonas aquamarina. Growth was inhibited at 4.0 mM Cr (VI), and reduction of Cr (VI) in the presence of 80 g l−1 NaCl was highlighted. Immobilized cells showed removal of Cr (VI) from sediment leachate. The cell free extract reduced Cr (VI) with a maximum of activity at pH 6.5 and at temperature of 28 °C, in the presence of NADH. Cr (VI) reduction activity was improved by Cu2+ and Fe2+ additions, whereas Hg2+ depleted it. Free and immobilized cells of the isolate could be used for bioremediation of Cr (VI)-contaminated sites. Cell free extract could represents an alternative in conditions where the whole cells result difficult to apply. A bacterial strain of the genus Halomonas is characterized in term of whole cells and cell-free extract Cr(VI)-reduction. The results suggest a good potential for bioremediation processes, in particular concerning detoxification of saline polluted environments.

► An efficient hexavalent chromium reduction by whole cells and cell free extract of Halomonas acquamarina.
► Chromate removal capacity of immobilized Halomonas aquamarina cells of 91.2% from sediments leachate.
► Hexavalent chromium reduction at moderate halophilic conditions by whole cells.