Which organism anaerobically reduces sulfates to hydrogen sulfide or metal sulfide?

Desulfovibrio is a genus of gram-negative bacteria known for its ability to anaerobically reduce sulfates to hydrogen sulfide (H2S) or metal sulfides. This metabolic process is an important component of the sulfur cycle, as it helps in the recycling of sulfur in various ecological niches, primarily in marine and sedimentary environments. Desulfovibrio species are often found in anaerobic conditions, such as deep-sea sediments or in the gut of some animals, where they perform sulfate reduction.

The other organisms listed do not share this specific metabolic capability. Escherichia coli primarily ferments sugars and can survive in both aerobic and anaerobic environments but does not reduce sulfates. Streptococcus bacteria are typically known for lactic acid fermentation rather than sulfate reduction, and Clostridium species, while they are anaerobic and can ferment various substrates, do not specifically reduce sulfate to hydrogen sulfide in a manner comparable to Desulfovibrio. Hence, Desulfovibrio is identified as the correct choice for the anaerobic reduction of sulfates.