Vanadium reduction by bacterial isolates from South African mines

English: In 1996, members of the Princeton group isolated a thermophilic Fe (III) reducing bacterium from a South African gold mine. Further collections at other mines confirmed that the mining environment harbors distinctive microbial populations, which may have novel applications. The purpose of this study was then to screen bacterial mine isolates for metal reducing capabilities. The bacteria where screened for their resistance to vanadium. Of the group of bacteria studied, one isolate showed high vanadium reducing capability. This unique characteristic was further studied, as well as it’s suitability as a bioremediation tool. The bacterial isolates were screened for vanadate resistance under aerobic, anaerobic and micro-aerophilic conditions. The tolerant isolates were then subjected to whole cell reduction under both aerobic and anaerobic conditions. It was found that not all of the tolerant isolates could reduce vanadate, and that vanadate reduction was enhanced under anaerobic conditions. The isolate which had the highest reduction rate under both aerobic and anaerobic conditions were selected for further experiments. The isolate was identified as belonging to the genus Enterobacter by using 16S rDNA sequencing. Sequencing results was confirmed using both the API 20E and the Biolog system. The isolate was designated as Enterobacter sp.EV-SA01, where EV refers to the place of isolation namely UEvUander gold mine. The maximum vanadate reduction by this microorganism during growth was associated with the early stationary phases, while the optimum conditions for growth were a neutral pH and a temperature between 37 to 39°C. Experiments to elucidate the protein(s) involved with vanadate reduction showed that the majority of the activity was associated with the membranes. The protein(s) responsible for the activity could be released from the membranes by treatment with detergents, but further characterization of the vanadate reducing activity was done using whole cells. The protein(s) showed optimum activity at pH 7 which corresponded with the optimum pH for growth, while optimum temperature was slightly higher at 45°C. A variety of electron donors could be utilized by the bacteria under both aerobic and anaerobic conditions, but the vanadate reducing ability was much higher under anaerobic conditions irrespective of which electron donor was used, with sodium lactate being the preferred electron donor. The in situ reduction experiments showed that the bacteria will be suitable as a bioremediation tool as it was able to survive in situ and reduce the vanadate present. This research has shown new aspects of vanadium reduction, the results can be explored in further studies to refine the bioremediation application of this bacterium. Also, it should be determined whether vanadium reduction in this microorganism is simply a detoxification process or if it has a dissimilatory role. A means to purify the vanadium reducing protein(s) and subsequent characterization should also be explored further.