Polycladomyces zharkentensis sp. nov., a novel thermophilic cellulose- and starch-degrading member of the Bacillota from a geothermal aquifer in Kazakhstan.

A thermophilic, aerobic and heterotrophic filamentous bacterium, designated strain ZKZ2 ^T , was isolated from a pipeline producing hydrothermal water originating from a >2.3 km deep subsurface geothermal source in Zharkent, Almaty region, Kazakhstan. The isolate was Gram-stain-positive, non-motile, heat-resistant and capable of producing a variety of extracellular hydrolases. Growth occurred at temperatures between 55 and 75 °C, with an optimum around 70 °C, and at pH values between 5.5 and 9.0, with an optimum at pH 7.0-7.5 with the formation of aerial mycelia; endospores were produced along the aerial mycelium. The isolate was able to utilize the following substrates for growth: glycerol, l-arabinose, ribose, d-xylose, d-glucose, d-fructose, d-mannose, rhamnose, d-mannitol, methyl-d-glucopyranoside, aesculin, salicin, cellobiose, maltose, melibiose, sucrose, trehalose, melezitose, raffinose, starch, turanose and 5-keto-gluconate. Furthermore, it was able to hydrolyse carboxymethylcellulose, starch, skimmed milk, Tween 60 and Tween 80. The major cellular fatty acids were iso-C _15 : 0 , iso-C _{17 : 0} , iso-C _16 : 0 and C _16 : 0 . Our 16S rRNA gene sequence analysis placed ZKZ2 ^T within the genus Polycladomyces , family Thermoactinomycetaceae , with the highest similarity to the type species Polycladomyces abyssicola JIR-001 ^T (99.18 % sequence identity). Our draft genome sequence analysis revealed a genome size of 3.3 Mbp with a G+C value of 52.5 mol%. The orthologous average nucleotide identity value as compared to that of its closest relative, P. abyssicola JIR-001 ^T , was 90.23 %, with an in silico DNA-DNA hybridization value of 40.7 %, indicating that ZKZ2 ^T represents a separate genome species. Based on the phenotypic and genome sequence differences from the other two Polycladomyces species, we propose that strain ZKZ2 ^T represents a novel species, for which we propose the name Polycladomyces zharkentensis sp. nov. The type strain is ZKZ2 ^T (=CECT 30708 ^T =KCTC 43421 ^T ).