Bromate Reduction By Rhodococcus Sp Br-6 In The Presence Of Multiple Redox Mediators

A bromate (BrO3-)-rechicing bacterium, designated Rhodococcus sp. strain Br-6, was isolated from soil. The strain reduced 250 mu M bromate completely within 4 days under growth conditions transitioning from aerobic to anaerobic conditions, while no reduction was observed under aerobic and anaerobic growth conditions. Bromate was reduced to bromide (Br-) stoichiometrically, and acetate was requited as an electron donor. Interestingly, bromate reduction by strain Br-6 was significantly dependent on both ferric iron and a redox dye 2,6-dichloroindophenol (DCIP). Cell free extract of strain Br-6 showed a dicumarol-sensitive diaphorase activity, which catalyzes the reduction of DCIP in the presence of NADH. Following abiotic experiments showed that the reduced form of DCIP was reoxidized by ferric iron, and that the resulting ferrous iron reduced bromate abiotically. Furthermore, activity staining of the cell free extract revealed that one of diaphorase isoforms possessed a bromate-reducing activity. Our results demonstrate that strain Br-6 utilizes, multiple redox mediators, that is, DCIP and ferric iron, for bromate reduction. Since the apparent rate of bromate reduction by this strain (60 mu M day(-1)) was 3 orders of magnitude higher than that of known bromate-reducing bacteria, it could be applicable to removal of this probable human carcinogen from drinking water.