Anoxybacillus karvacharensis sp. nov., a novel thermophilic bacterium isolated from the Karvachar geothermal spring in Nagorno-Karabakh

Twelve thermophilic Anoxybacillus strains were isolated from sediment and water samples from a Karvachar hot spring located in the northern part of Nagorno-Karabakh. Based on phenotypic, chemotaxonomic and phylogenetic characteristics, one of the isolates, designated strain K1(T), was studied in detail. The cells are straight, motile rods that are 0.2-0.4x2.3-7.2 mu m in size. The strain is a Gram-stain-positive, moderately thermophilic facultative anaerobe with an optimum growth temperature of 60-65 degrees C and a growth temperature range of 45-70 degrees C. Growth of strain K1(T) was observed at pH 6-11 (optimum, pH 8-9) and was inhibited in the presence of NaCl concentrations above 2.5 % (optimum, 1-1.5%). The isolate could utilize a wide variety of carbon sources, including D-arabinose, D-ribose, D-galactose, D-fructose, D-mannitol, maltose, aesculin, melibiose, sucrose, trehalose, raffinose, amidone, glycogen, turanose, D-lyxose, D-tagatose, potassium gluconate and 2-ketogluconate. The strain was able to hydrolyse starch, casein and gelatin, was positive for oxidase and catalase, and reduced nitrate to nitrite, but was negative for H2S production. Production of urease and indole was not observed. The major cellular fatty acids were C-15:0 iso, C-16:0 and C-17:0 iso (52.5, 13.6 and 19.6% of total fatty acids, respectively). Strain K1(T) shares >99 % 16S rRNA sequence similarity and a genomic average nucleotide identity value of 94.5 % with its closest relative, Anoxybacillus flavithermus DSM 2641(T), suggesting that it represents a separate and novel species, for which the name Anoxybacillus karvacharensis sp. nov. is proposed. The type strain of Anoxybacillus karvacharensis is K1(T) (=DSM 106524(T)=KCTC 15807(T)).

Automated summary

Twelve thermophilic Anoxybacillus strains were isolated from a hot spring in Nagorno-Karabakh, with strain K1(T) being Gram-stain-positive, moderately thermophilic, and capable of growth within specific temperature and pH ranges. The strain showed high similarity to Anoxybacillus flavithermus DSM 2641(T) but was proposed as a separate species, Anoxybacillus karvacharensis, based on genetic analysis.