The cultivation medium contained the following (g L−1): (NH4)2SO4, 0.3; CaCl2 · 6H2O, 0.05; MgSO4 · 7H2O, 0.1; NaHCO3, 0.3; 10% phosphate buffer (pH 7.0), 0.1; HEPES buffer (pH 7.0), 3.0; KNO3, 0.3; CH3COONa; 0.15; vitamins and trace elements (Pfennig & Lippert, 1966); agar (Difco), 5.0; pH 6.7 at 30 °C. Before inoculation, 0.2 mL of a freshly IWR-1 purchase prepared FeS suspension (Hanert, 1981) was added to each tube per 10 mL of the medium. The incubation time was 2–3 weeks. The FOB strain Sp-1 was isolated

by terminal 10-fold dilutions in the same agar medium. The colonies were then transferred into liquid medium. Cultivation of the strain Sp-1 and subsequent experiments were carried out in liquid mineral media in anaerobic conditions and in media

supplemented with acetate (when FeSO4 was used as an electron donor). The methods of cells morphology and ultrastructure PD332991 investigation, cultural, analytical and biochemical methods as well as genetic, phylogenetic and chemotaxonomic methods were described earlier (Sorokina et al., 2012). The polar lipids were analysed by thin-layer chromatography (Kieselgel 60, 10 × 10 cm; Merck, Germany) using the phospholipid standards (Sigma; Bej et al., 1991). All experiments were performed at least three times, in the figures and tables are average results of representative experiments. The number of FOB in the spring water did not exceed 10 cells mL−1, while in the freshly precipitated FeS sediment at the spring outlet, it was as high as 105–107 cells mL−1. The freshly precipitated FeS sediment collected at the border of the redox zone was used as the inoculum. In agar medium, the bacteria formed small (2–3 mm in diameter), loose spherical colonies. The colonies were orange-coloured because of the presence of iron oxides. In liquid medium of the same composition, an

ochreous precipitate was formed at the bottom of the vials. The pure culture of FOB was isolated with 10-fold dilutions of the individual colonies under anaerobic conditions in liquid medium with FeS and nitrates. The cells of strain Sp-1 were short thin vibrios, 0.3 × 0.8–1.3 μm, motile because of a single polar flagellum (Fig. 1a and c). The cells divided by binary fission. On the surface of the cells grown with Fe(II), iron oxides were Aprepitant accumulated (Fig. 1b and d). The Gram reaction was negative. The heavy incrustation of the cells by iron oxides raises a question whether it stops active metabolism and further growth. Despite several suggestions circulating in the literature on possible mechanisms of dealing with the inhibitory influence of iron incrustation on growth and metabolism of anaerobic FOB (Sobolev & Roden, 2001, 2002; Schippers & Jørgensen, 2002; Kappler & Newman, 2004), we believe that the formation of amorphous iron oxides does not significantly influence diffusion of nutrients and cell growth in this group.