Vanadium reduction by bacterial isolates from South African mines

[摘要] English: In 1996, members of the Princeton group isolated a thermophilic Fe (III) reducingbacterium from a South African gold mine. Further collections at other minesconfirmed that the mining environment harbors distinctive microbial populations,which may have novel applications. The purpose of this study was then to screenbacterial mine isolates for metal reducing capabilities. The bacteria where screenedfor their resistance to vanadium. Of the group of bacteria studied, one isolateshowed high vanadium reducing capability. This unique characteristic was furtherstudied, 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 subjectedto whole cell reduction under both aerobic and anaerobic conditions. It was foundthat not all of the tolerant isolates could reduce vanadate, and that vanadatereduction was enhanced under anaerobic conditions. The isolate which had thehighest reduction rate under both aerobic and anaerobic conditions were selected forfurther experiments. The isolate was identified as belonging to the genusEnterobacter by using 16S rDNA sequencing. Sequencing results was confirmedusing both the API 20E and the Biolog system. The isolate was designated asEnterobacter sp.EV-SA01, where EV refers to the place of isolation namely UEvUandergold mine. The maximum vanadate reduction by this microorganism during growthwas associated with the early stationary phases, while the optimum conditions forgrowth were a neutral pH and a temperature between 37 to 39°C.Experiments to elucidate the protein(s) involved with vanadate reduction showed thatthe majority of the activity was associated with the membranes. The protein(s)responsible for the activity could be released from the membranes by treatment withdetergents, but further characterization of the vanadate reducing activity was doneusing whole cells. The protein(s) showed optimum activity at pH 7 whichcorresponded with the optimum pH for growth, while optimum temperature wasslightly higher at 45°C. A variety of electron donors could be utilized by the bacteriaunder both aerobic and anaerobic conditions, but the vanadate reducing ability was much higher under anaerobic conditions irrespective of which electron donor wasused, with sodium lactate being the preferred electron donor. The in situ reductionexperiments showed that the bacteria will be suitable as a bioremediation tool as itwas able to survive in situ and reduce the vanadate present.This research has shown new aspects of vanadium reduction, the results can beexplored in further studies to refine the bioremediation application of this bacterium.Also, it should be determined whether vanadium reduction in this microorganism issimply a detoxification process or if it has a dissimilatory role. A means to purify thevanadium reducing protein(s) and subsequent characterization should also beexplored further.

[发布机构] University of the Free State