Abstract
Bacterial community analyses of samples from a pilot plant for the treatment of acid mine drainage (AMD) from the lignite-mining district in Lusatia (East Germany) had previously demonstrated the dominance of two groups of acidophilic iron oxidizers: the novel candidate genus “Ferrovum” and a group comprising Gallionella-like strains. Since pure culture had proven difficult, previous studies have used genome analyses of co-cultures consisting of “Ferrovum” and a strain of the heterotrophic acidophile Acidiphilium in order to obtain insight into the life style of these novel bacteria. Here we report on attempts to undertake a similar study on Gallionella-like acidophiles from AMD. Isolates belonging to the family Gallionellaceae are still restricted to the microaerophilic and neutrophilic iron oxidizers Sideroxydans and Gallionella. Availability of genomic or metagenomic sequence data of acidophilic strains of these genera should, therefore, be relevant for defining adaptive strategies in pH homeostasis. This is particularly the case since complete genome sequences of the neutrophilic strains G. capsiferriformans ES-2 and S. lithotrophicus ES-1 permit the direct comparison of the metabolic capacity of neutrophilic and acidophilic members of the same genus and, thus, the detection of biochemical features that are specific to acidophilic strains to support life under acidic conditions. Isolation attempts undertaken in this study resulted in the microaerophilic enrichment culture ADE-12-1 which, based on 16S rRNA gene sequence analysis, consisted of at least three to four distinct Gallionellaceae strains that appear to be closely related to the neutrophilic iron oxidizer S. lithotrophicus ES-1. Key hypotheses inferred from the metabolic reconstruction of the metagenomic sequence data of these acidophilic Sideroxydans strains include the putative role of urea hydrolysis, formate oxidation and cyanophycin decarboxylation in pH homeostasis.
Highlights
The lignite-mining district in Lusatia (Germany) is rich in pyrite and marcasite
Illumina-based sequence analysis of the metagenomic DNA extracted from enrichment culture ADE-12-1 provided 20,563,010 GAII and 10,406,346 MiSeq sequence reads which were assembled into 9456 contigs totalling 56.8 Mb of metagenomic sequence information
The findings reported here indicate that acidophilic Sideroxydans strains have a wider repertoire of metabolic features available in this respect than found in the genome sequence of the neutrophilic S. lithotrophicus strain ES-1 (Emerson et al, 2013)
Summary
The lignite-mining district in Lusatia (Germany) is rich in pyrite and marcasite. Mining activities, cause a dramatic increase in pyrite/marcasite surface exposure and subsequent oxidative processes which, in turn, result in acidic waters with high sulfate and ferrous iron loads. Acidophilic iron-oxidizing bacteria are largely responsible for the generation of AMD, they can contribute to the reduction of its iron and of some of its sulfate load via ferrous iron oxidation with subsequent precipitation of ferric iron hydroxysulfate minerals (Janneck et al, 2010) An example of such a biotechnological process is provided by the treatment plant Tzschelln (Janneck et al, 2010), a 10qm pilot-scale operation (Figure 1) for the bioremediation of AMD water from the open-pit lignite mine Nochten (Lusatia, Germany). This process involves, in essence, the aeration of AMD water and subsequent ferrous iron oxidation by acidophilic iron-oxidizing microorganisms. Schwertmannite has various applications as a pigment or as a sorbent for the removal of arsenic from aqueous solutions (Janneck et al, 2010)
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