A new representative of neutrophilic iron oxidizing bacteria was isolated from the iron containing sediments of the brackish low temperature iron rich spring of the Staraya Russa Resort (Novgorod region, Russia). The cells of strain Hf1 were thin, slightly curved rods, motile by means of a single polar flagellum. The bacterium reproduced by binary division and was capable of producing rosettes. Optimal growth was observed within the pH range of 6.2-8.5 (with an optimum at 7.5), at 9-38°C (with an optimum at 30°C), and in the salinity range of 0.1-8.5% NaCl (with an optimum at 1%). The organism was a facultative anaer obe. The strain was capable of mixotrophic and organoheterotrophic growth. Fe(II) oxidation occurred under anaerobic conditions via reduction of and N 2 O, or under microaerobic conditions with oxygen as an electron acceptor. According to phylogenetic analysis based on the comparison of the 16S rRNA gene sequences, the strain was closest to the organotrophic marine bacterium Hoeflea phototrophica (98.5% simi larity). The level of DNA-DNA homology with the type species of the genus Hoeflea was 19%. The DNA G + C base content was 57.5 mol %. According to its phenotypic and chemotaxonomic properties, as well as to the results of phylogenetic analysis, strain Hf1 was classified into the genus Hoeflea of the family Phyllo bacteriaceae, order Rhizobiales of the phylum Alphaproteobacteria as a novel species, Hoeflea siderophila sp. nov. The type strain is Hf1 T (=DSM 21587 = VKM A7094). The GenBank accession number for the 16S rRNA gene sequences of strain Hf1 T is EU670237.
A neutrophilic Fe(II)‐oxidizing bacterium was isolated from the redox zone of a low‐salinity spring in Krasnodar krai (Russia), at the FeS–Fe(OH)3 interface deposited at the sediment surface. The cells of strain Sp‐1 were short, thin motile vibrioids with one polar flagellum dividing by binary fission. The optimal values and ranges for pH and temperature were pH 6.2 (5.5–8) and 35 °C (5–45 °C), respectively. The organism was a facultative anaerobe. Strain Sp‐1 was capable of organotrophic, lithoheterotrophic and mixotrophic growth with Fe(II) as an electron donor. The denitrification chain was ‘disrupted’. Oxidation of Fe(II) was coupled to reduction of NO3 − to NO2 − or of N2O to N2, as well as under microaerobic conditions, with O2 as an electron acceptor. The DNA G+C content was 64.2 mol%. According to the results of phylogenetic analysis, the strain was 10.6–12% remote from the closest relatives, members of the genera Sneathiella, Inquilinus, Oceanibaculum and Phaeospirillum within the Alphaproteobacteria. Based on its morphological, physiological and taxonomic characteristics, together with the results of phylogenetic analysis, strain Sp‐1 is described as a member of a new genus Ferrovibrio gen. nov., with the type species Ferrovibrio denitrificans sp. nov. and the type strain Sp‐1T (= LMG 25817T = VKM B‐2673T).
Abundance and structure of the communities of neutrophilic lithotrophic iron oxidizing bacteria (FeOB) inhabiting four low mineralized ferruginous springs of the Marcial Waters Resort (South Karelia, Russia) and the brackish chalybeate spring of the Staraya Russa Resort (Novgorod region, Russia), were investigated, as well as the physicochemical conditions of these environments. In fresh iron containing pre cipitates collected near the spring outlets and within the spring discharge areas, as well as along the spring watercourses, the numbers of unicellular FeOB enumerated on nutrient media ranged from 10 5 to 10 7 cells per 1 mL of sediments irrespective of the initial Fe(II) concentration (11-126 mg L -1 ). In the spring waters and along the spring watercourses inhabited by iron oxidizing bacteria, the concentration of dissolved oxygen did not exceed 0.05-0.1 mg L -1 . Unicellular FeOB were predominant in three springs, while in the springs with relatively low Fe(II) concentrations (11-22 mg L -1 ), various morphological forms of Gallionella and uncultured forms of the iron oxidizing bacterium Toxothrix trichogenes prevailed. In the model experiments with the water samples collected in the ferruginous springs and bogs under controlled conditions, the frac tionation of stable iron isotopes and the rate of iron oxidation were found to depend on the oxygen regime and, to a lesser extent, on the initial Fe(II) concentration. The maximum enrichment of the iron oxides formed during the simulation experiments with the light 54 Fe isotope was observed during bacterial oxidation under microaerobic conditions at O 2 concentrations of 0.1-0.3 mg L -1 and in the cultures of iron oxidizing bacteria. During the abiogenic oxidation of Fe(II), the extent of stable isotope fractionation was 1.5-2 times lower. Enrichment of Fe(III) oxides with the light 54 Fe isotope (3 to 5 fold) was considerably lower at high rates of both the biogenic and abiogenic processes of iron oxidation under aerobic conditions; however, it was more intense during the bacterial processes. Comparison of the rates of enrichment of Fe(III) oxides with the light isotope during the model experiments with pure and enrichment cultures of iron oxidizing bacteria from the sediments of ferruginous springs and bogs revealed that the biogenic factor plays a key role in the oxidation processes of the iron cycle, as well as in the differentiation of the composition of stable iron isotopes in the studied ecosystems.
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