, 1998). In the medium with acetate and Fe(II), however, the concentration did not exceed 0.15 mM because of its chemical interaction with Fe(II) (Fig. 3a). When gaseous nitrous oxide (N2O) was substituted for as an electron acceptor, growth of FOB resulted in N2 accumulation in the gas phase, while no inhibition of cell growth occurred throughout 17 days of the experiment (Fig. 3b). These results indicate the presence of the ‘disrupted’ denitrification chain in the strain Sp-1,
as was shown earlier for a new species Hoeflea siderophila (Sorokina et al., 2012): During anaerobic organotrophic growth at acetate concentration in the medium increased to 500 mg L−1, nitrite accumulation up to 6.4 mM after a short time (7 days) resulted in suppression of bacterial growth. Low nitrite reductase activity probably explains nitrate reduction only to nitrite in a large group of the known organoheterotrophic denitrifying microorganisms. Strain Sp-1 was capable of organoheterotrophic Nivolumab growth on acetate under anaerobic conditions with Ar–N2O in the gas phase; acetate consumption was as high as 7.2 mg (mg protein)−1 (Table 2). Addition of FeSO4 to the medium resulted
in a 14% increase of the cell yield accompanied by a 15% decrease of acetate consumption for protein synthesis in energetic and constructive metabolism. In acetate-free medium, while the Anti-infection Compound Library mouse growth was insignificant, with the cell yield not exceeding 5 mg protein L−1, the amount of oxidized Fe(II) (12 mg mg protein−1) was twice as high as in the case of mixotrophic growth with acetate. Weak but steady growth (3 mg protein L−1 after long-time cultivation) under anaerobic conditions was observed in mineral medium without ferrous iron and acetate. Protein was probably synthesized in the course of organoheterotrophic growth using the trace amounts of contaminating organic compounds arriving from the gas phase, as was known for other microorganisms. Thus, in the case of strict limitation of constructive metabolism by organic matter and elevated amounts
of Fe(II) oxidized per unit protein, bacterial growth was probably strictly lithoheterotrophic, with utilization of contaminating organic compounds for constructive metabolism alone, while Fe(II) was oxidized for the energy metabolism. Farnesyltransferase Molecular genetic analysis of the functional genes responsible for autotrophy in strain Sp-1 showed the absence of the genes of RuBisCO and isocitrate lyase, the key enzymes of the Calvin cycle and the reductive tricarboxylic acid cycle, respectively. This result confirmed the absence of capacity for lithoautotrophic growth. Thus, strain Sp-1 is able to oxidize iron for mixotrophic and lithoheterotrophic growth; the latter should be considered as a variant of mixotrophy. According to the results of multiphase analysis, strain Sp-1 exhibited significant differences from the most closely related genera Sneathiella, Inquilinus, Oceanibaculum and Phaeospirillum of the Alphaproteobacteria.