Iron-Reducing Microbial Communities of the Lake Baikal Low-Temperature Bottom Sediments

Abstract

Psychroactive enrichment cultures reducing anthraquinone 2,6-disulfonate (AQDS) and soluble complexes of ferric iron at 5–20°C were isolated from the samples of Lake Baikal bottom sediments collected at the depths of 404 to 1396 m. Cultivation resulted in production of up to 6 mM Fe(II), which was over 50% of the initial Fe(III) concentration in the medium, and of 5.5 mM AH₂QDS (~30% of the initial quinone concentration). The enrichment culture of iron-reducing bacteria St3 used Fe(III) citrate as the terminal electron acceptor, oxidizing formate from 6.5 to 2.0 g L^–1 at 15°C. Phylogenetic analysis showed that the initial samples of the Lake Baikal bottom sediments and the enrichments obtained from these samples contained the taxa of classes Alpha- and Betaproteobacteria, which were closely related to bacteria capable of oxidizing aromatic compounds using inorganic electron acceptors, including ferric iron.