GENETIC DIVERSITY AND EXPRESSION OF THE [NIFE] HYDROGENASE LARGE-SUBUNIT GENE OF DESULFOVIBRIO SPP. IN ENVIRONMENTAL-SAMPLES

The genetic diversity and expression of the [NiFe] hydrogenase large-s ubunit gene of Desulfovibrio spp. in environmental samples were determ ined in order to show in parallel the existing and active members of D esulfovibrio populations. DNA and total RNA were extracted from differ ent anaerobic bioreactor samples; RNA was transcribed into cDNA. Subse quently, PCR was performed to amplify a ca.-440-bp fragment of the [Ni Fe] hydrogenase large-subunit gene and its mRNA Denaturing gradient ge l electrophoresis analysis was used to separate the PCR products accor ding to their sequence and thereby to visualize tile individual commun ity members. Desulfovibrio strains corresponding to amplified [NiFe] h ydrogenase transcripts were regarded as metabolically active, because in pure cultures transcripts were detectable in exponentially growing cells but not in cultures in the stationary phase. DNA sequencing and comparative sequence analysis were used to identify the detected organ isms on the basis of their [NiFe] hydrogenase sequences. The genes of characterized Desulfovibrio spp. showed a considerable extent of diver gence (ca. 30%), whereas sequences obtained from bacterial populations of the bioreactors showed a low level of variation and indicated the coexistence of closely related strains probably belonging to the speci es Desulfovibrio sulfodismutans. Under methanogenic conditions, all de tected populations were active; under denitrifying conditions, no [NiF e] hydrogenase mRNA was visible. Changes in activity and composition o f Desulfovibrio populations caused by changes in the environmental con ditions could be monitored by using the approach described in this stu dy.