Bacterial and archaeal populations associated with freshwater ferromanganous micronodules and sediments

Biology is believed to play a large role in the cycling of iron and mangane se in many freshwater environments, but specific microbial groups indigenou s to these systems have not been well characterized. To investigate the pop ulations of Bacteria and Archaea associated with metal-rich sediments from Green Bay, WI, we extracted nucleic acids and analysed the phylogenetic rel ationships of cloned 16S rRNA genes. Because nucleic acids have not been ro utinely extracted from metal-rich samples, we investigated the bias inheren t in DNA extraction and gene amplification from pure MnO2 using defined pop ulations of whole cells or naked DNA, From the sediments, we screened for m anganese-oxidizing bacteria using indicator media and found three isolates that were capable of manganese oxidation, In the phylogenetic analysis of b acterial 16S rRNA gene clones, we found two groups related to known metal-o xidizing genera, Leptothrix of the beta -Proteobacteria and Hyphomicrobium of the alpha -Proteobacteria, and a Fe(III)-reducing group related to the M agnetospirillum genus of the alpha -Proteobacteria, Groups related to the m etal-reducing delta -Proteobacteria constituted 22% of the gene clones, In addition, gene sequences from one group of methanogens and a group of Crena rchaeota, identified in the archaeal gene clone library, were related to th ose found previously in Lake Michigan sediments,