<Emphasis Type="Italic">Magnetospirillum aberrantis</Emphasis> sp. nov., a new freshwater bacterium with magnetic inclusions

A new strain of spirilla, SpK, was isolated from the bottom sediments of Ol’khovka River near Kislovodsk (Caucasus). The bacteria (0.4 ±1.5 μm) were motile, with polar flagella. They grew within the temperature range from 20 to 45°C, with the optimum at 31°C. The pH growth optimum was at 6.5–6.9. The main type of metabolism was respiratory, chemoorganotrophic. The organism was microaerophilic, with the growth optimum at 1–5% O₂ in the gas phase. Catalase activity was absent, while oxidase activity was detected. Good growth occurred in media with various organic acids, especially acetate and fumarate. Sugars and alcohols were not utilized. Importantly, the strain did not grow on casein hydrolysate and grew well on glycerol. The bacteria contained the RuBisCo cbbm gene (form II). Thiosulfate, ammonium, and ferrous iron were not used as electron donors for autotrophic growth. Unlike sulfate, thiosulfate, ferric iron, or perchlorate, nitrate could be used as an electron acceptor for photoheterotrophic growth. Strain SpK was characterized by the ability to form small, dense intracellular granules (30–40 nm) occurring in clusters or short chains. These inclusions were shown to have magnetic properties. Unlike magnetosomes, the granules did not form long chains. Invaginations of vesicular membranes similar to those found in the known magnetosomeforming microorganisms were observed. The DNA G + C content was 62.6 mol %. Ubiquinone Q ₁₀ was present. The main fatty acids were 18:1ω7 (58.19%), 16:0 (19.23%), 16:1ω7 (11.12%), and 18:0 (1.91%). Polyhydroxybutyrate and polyphosphates were the storage compounds. Analysis of the 16S rRNA gene sequence revealed that the strain belonged to the phylum Alphaproteobacteria, family Rhodospirillaceae, genus Magnetospirillum. Strain SpK formed an isolated cluster on the phylogenetic tree. The similarity between strain SpK and the known Magnetospirillum species was from 96.1 to 96.4%. Thus, the new microorganism was classified as a new species of the genus Magnetospirillum, Magnetospirillum aberrantis sp. nov.