Proposal of Thermoactinomyces mirandus sp. nov., a filamentous, anaerobic bacterium isolated from a biogas plant.

We isolated a filamentous, thermophilic, and first anaerobic representative of the genus Thermoactinomyces, designated strain AMNI-1T, from a biogas plant in Tyrol, Austria and report the results of a phenotypic, genetic, and phylogenetic investigation. Strain AMNI-1T was observed to form a white branching mycelium that aggregates into pellets when grown in liquid medium. Cells could primarily utilize lactose, glucose, and mannose as carbon and energy sources, with acetate accelerating and yeast extract being mandatory for growth. The optimum growth temperature and pH turned out to be 55 °C and pH 7.0, respectively, with an optimum NaCl concentration of 0-2% (w/v). 16S rRNA gene sequence comparison indicated that the genetic relatedness between strain AMNI-1T and Thermoactinomyces intermedius, Thermoactinomyces khenchelensis, and Thermoactinomyces vulgaris was less than 97%. The G + C content of the genomic DNA was 44.7 mol%. The data obtained suggest that the isolate represents a novel and first anaerobic species of the genus Thermoactinomyces, for which the name Thermoactinomyces mirandus is proposed. The type strain is AMNI-1T (= DSM 110094T = LMG 31503T). The description of the genus Thermoactinomyces is emended accordingly.