Sulfate-reducing bacteria (SRB) of the genus Desulfovibrio have up to three different hydrogenases all catalyzing the reaction H-2 half arrow left over half arrow right 2H(+) + 2e. These enzymes allow Desulfovibr io to derive energy for maintenance and growth from the lithotrophic reaction: 4H(2) + SO42- --> S2- + 4H(2)O. One of the hydrogenases, the [NiFe] hydrogenase, is present in all of 22 Desulfovibrio species that were investigated. Use of the gene for this hydrogenase as a Desulfovibr io-specific probe allowed the presence of different Desulfovibrio species in oil field production waters to be detected. These results provided only a partial description of the SRB population, because Desulfovibrio is only one of several SRB genera present. These other genera were not detectable with the hydrogenase gene probe. In searching for a more generally applicable DNA hybridization method it was found that the entire chromosomal DNA of a given species, can serve as a specific probe for its detection. Total community DNA isolated from oil field samples can be economically analyzed by a reverse genome probe approach, which has indicated that the sessile population present at metal surfaces is often dominated by selected Desulfovibrio io species. This finding is a first step in a more detailed analysis of the roles of these bacteria in metal corrosion and oil field souring, which have a negative impact on the processing of oil.