A chromate reducing strain, Pseudomonas mendocina transformed hexavalent chromium to its trivalent form which precipitated as chromic hydroxide in the medium. Studies with respiratory inhibitors in conjunction with molar growth yield data indicated that chromate is not used as the terminal electron acceptor by this organism but probably serves as an auxiliary oxidant that helps in generation of oxidized cofactors necessary in cellular metabolism. Chromate reduction by P. mendocina is mediated by a periplasmic chromate reductase having molecular weight of approximately 183 KDa. The temperature and pH optima of the enzyme are 70 degrees C and 8.5, respectively. Purified enzyme exhibited a K-m of 289 mu M chromate and a V-max of 625 mu M chromate reduced/min/mg protein.

Pseudomonas mendocina when added in soil microcosms could immobilize 100 μg (2 mM) chromate/g soil in 8 h by converting it into trivalent form. The chromate-contaminated soils, after microbiological treatment, supported growth of wheat seedlings without exerting any toxic effects. The method is potentially useful in the bioremediation of chromate-contaminated sites. © Rapid Science Ltd. 1998