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delta proteobacterium sp. MLMS-1
   
   
 

Recently isolated from Mono Lake, this delta-Proteobacterium (16S rRNA gene GenBank AY459365) respires arsenate by using sulfide as its electron donor (Hoeft et al., 2004). It can fix CO2 into cell carbon, however, RuBisCo enzymes (form I and II) have not as yet been detected. This suggests either a novel RuBisCo or that it could be fixing carbon via acetyl CoA synthetase or a reverse TCA cycle. This organism appears to be the first representative of an obligate chemoautotroph that is also an obligate arsenate-respirer. This form of metabolism could be significant as many subsurface aquifers are also poor in organic materials that would normally serve as electron donors to fuel arsenate-respiration. Hence, arsenate-reduction could be fueled by the oxidation of reduced minerals like sulfide, thereby circumventing the need for organics. There is currently a debate amongst hydrologists as to what type of organics are driving subsurface arsenate reduction in Bangladesh; buried subsurface peat or draw down of surface associated organics (fecal matter and agricultural wastes). Chemoautotrophy linked to sulfide, or perhaps H2 as well, offers another means by which this reaction could also be achieved.