Phylogenetic composition of enrichment cultures of thermophilic prokaryotes reducing poorly crystalline Fe(III) oxide with and without direct contact between the cells and mineral

Abstract

Thirty enrichment cultures of thermophilic microorganisms were obtained from Kamchatka terrestrial hydrotherms that reduced insoluble poorly crystalline Fe(III) oxide (ferrihydrite) with and without direct contact between the cells and the mineral. Restricted access to the Fe(III) mineral was achieved by incorporation of ferrihydrite into alginate beads. According to phylogenetic analysis of 22 enrichment cultures by denaturing gradient gel electrophoresis of 16S rRNA gene fragments, Firmicutes were predominant among bacteria in all the variants. Microorganisms of the phylogenetic types Aquificae, Bacteroidetes, Nitrospirae, Planctomycetes, Spirochaetes, Synergistetes, and Thermotogae were also revealed. The archaea revealed belonged to the genera Desulfurococcus, Pyrobaculum, and Thermofilum. In the case of free access to ferrihydrite, most of the phylotypes belonged to genera known for Fe(III) reduction. In the absence of direct contact with the mineral, together with known iron reducers, organisms for which ability to reduce Fe(III) was unknown were detected. Members of the genera Carboxydothermus, Thermoanaerobacter, and Thermotoga were detected most often both in the presence and absence of contact with ferrihydrite. These organisms probably possess efficient mechanisms for Fe(III) reduction within the experimental temperature range. Microbial phylogenetic diversity was higher when acetate, rather than lactate, was used as a potential electron donor.