Leptothrix cholodnii is a sheathed bacterium often found in metal-rich and oligotrophic aquatic environments. A bacterial strain that is able to degrade the NaOH-treated sheath of L. cholodnii was isolated. The isolate was a Gram-negative, aerobic and prosthecate bacterium. The optimum growth temperature and pH were 30 °C and pH 7.0, respectively. The DNA G+C content was 62.9 mol%. The major respiratory quinone was MK-6. A phylogenetic analysis based on the 16S rRNA gene indicated that the isolate is a member of the genus Prosthecobacter. The nearest relative was the type strain of Prosthecobacter vanneervenii, with a similarity of 97.1 %. However, the isolate does not possess the bacterial tubulin genes, btubA and btubB, unique to known species of the genus Prosthecobacter. It is proposed that the isolate represents a novel species, Prosthecobacter fluviatilis sp. nov. The type strain is HAQ-1T (=JCM 14805T =KACC 12649T =KCTC 22182T).
A moderately thermophilic, nitrate-reducing bacterium, strain Yu37-1T, was isolated from hot spring water from Yumata, Nagano, Japan. Cells of strain Yu37-1T were strictly anaerobic, Gram-negative, non-sporulating, motile by means of a single polar flagellum, vibrio-shaped and 1.4–2.0 μm long. The temperature and pH for optimum growth were 55 °C and pH 7.0–7.5, respectively. Strain Yu37-1T grew best in basal medium without the addition of NaCl. Acetate, pyruvate, lactate, fumarate, succinate, malate, yeast extract, peptone and Casamino acids were utilized as electron donors, with nitrate as the only electron acceptor. Ammonium was the end product from nitrate. The G+C content of the genomic DNA was 35.1 mol%. Phylogenetic analysis based on the 16S rRNA gene revealed that strain Yu37-1T could be accommodated in the family Deferribacteraceae and that its closest neighbours were members of the five genera of the family Deferribacteraceae, namely Deferribacter, Denitrovibrio, Flexistipes, Geovibrio and Mucispirillum, with similarities of only 83.2–86.2 %. The growth temperature and salinity range for growth of strain Yu37-1T differed from those of the phylogenetically related organisms. On the basis of phenotypic features and phylogenetic position, a novel genus and species are proposed, Calditerrivibrio nitroreducens gen. nov., sp. nov. Strain Yu37-1T (=NBRC 101217T =DSM 19672T) is the type strain of Calditerrivibrio nitroreducens.