Iron-reducing microorganisms in a landfill leachate-polluted aquifer: Complementing culture-independent information with enrichments and isolations

Using culture-independent 16S rRNA gene-based methods, we previously observed that Geobacteraceae were a major component of the microbial communities in the iron-reducing aquifer polluted by the Banisveld landfill, The Netherlands. However, phylogenetic information does not tell about the functional potential of the detected Geobacteraceae, nor can phylogenetic information easily be used to establish the presence of other iron-reducers. Therefore, we enriched for iron-reducing consortia using a range of culturing media, with various electron donors and acceptors and varying incubation conditions ( pH, temperature), and by applying dilution-to-extinction culturing. Enrichments and strains isolated from these enrichments were characterized by 16S rRNA gene-based methods. The number of culturable iron-reducers was less than 110 iron-reducing bacteria per gram of sediment. The Geobacter phylotype that was previously found to constitute a major part of the microbial communities in a part of the aquifer where organic matter was attenuated at a relatively high rate, was not isolated. The isolation of another Geobacter strain and Serratia, Clostridium, Rhodoferax and Desulfitobacterium strains suggest the presence of a diverse iron-reducing community. Physiological capabilities of the isolates are described and discussed in relation to the hydrogeochemistry and the high abundance of Geobacteraceae in the aquifer polluted by the Banisveld landfill.