Aims: The objectives of this work were to explore the diversity in Fe (III)-reducing enrichment cultures from the deep subsurface and to identify strains involved in metal reduction.
Methods and results: Analyses of 16S ribosomal RNA (rRNA) of enrichments, supplemented with hydrogen, acetate or pyruvate as an electron donor, identified three dominant operational taxonomic units (OTUs). All cultures exhibited considerable diversity (36-24 OTUs), even after being transferred at least nine times. Two OTUs were present in all three cultures, constituting about 65% of the total clones examined.
Conclusion: Dominant OTUs appeared to be most closely related to Thermoanaerobacter ethanolicus or T. kivui. One OTU, which is potentially responsible for autotrophic Fe (III) reduction, was only about 95% similar to T. ethanolicus and may represent a new species.
Significance and impact of the study: An unexpectedly high diversity was found in these enrichments and this diversity may be a feature that can be exploited.