Background: In order to study the mechanism of U(VI) reduction, the effect of deleting c-type cytochrome genes on the capacity of Geobacter sulfurreducens to reduce U(VI) with acetate serving as the electron donor was investigated.

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The goal of this project was to isolate representative Fe(III)-reducing bacteria from kaolin clays that may influence iron mineralogy in kaolin. Two novel dissimilatory Fe(III)-reducing bacteria, strains G12T and G13T, were isolated from sedimentary kaolin strata in Georgia (USA). Cells of strains G12T and G13T were motile, non-spore-forming regular rods, 1–2 μm long and 0.6 μm in diameter. Cells had one lateral flagellum. Phylogenetic analyses using the 16S rRNA gene sequence of the novel strains demonstrated their affiliation to the genus Geobacter. Strain G12T was most closely related to Geobacter pelophilus (94.7 %) and Geobacter chapellei (94.1 %). Strain G13T was most closely related to Geobacter grbiciae (95.3 %) and Geobacter metallireducens (95.1 %). Based on phylogenetic analyses and phenotypic differences between the novel isolates and other closely related species of the genus Geobacter, the isolates are proposed as representing two novel species, Geobacter argillaceus sp. nov. (type strain G12T=ATCC BAA-1139T=JCM 12999T) and Geobacter pickeringii sp. nov. (type strain G13T=ATCC BAA-1140T=DSM 17153T=JCM 13000T). Another isolate, strain R7T, was derived from a primary kaolin deposit in Russia. The cells of strain R7T were motile, spore-forming, slightly curved rods, 0.6×2.0–6.0 μm in size and with up to six peritrichous flagella. Strain R7T was capable of reducing Fe(III) only in the presence of a fermentable substrate. 16S rRNA gene sequence analysis demonstrated that this isolate is unique, showing less than 92 % similarity to bacteria of the Sporomusa–Pectinatus–Selenomomas phyletic group, including ‘Anaerospora hongkongensis’ (90.2 %), Acetonema longum (90.6 %), Dendrosporobacter quercicolus (90.9 %) and Anaerosinus glycerini (91.5 %). On the basis of phylogenetic analysis and physiological tests, strain R7T is proposed to represent a novel genus and species, Pelosinus fermentans gen. nov., sp. nov. (type strain R7T=DSM 17108T=ATCC BAA-1133T), in the Sporomusa–Pectinatus–Selenomonas group.