Abstract
A thermophilic poly(L-lactide)-degrading Gram-stain-positive filamentous bacterial strain that develops single spores on the aerial mycelium was isolated from forest soil at Srinagarind Dam, Kanchanaburi Province, Thailand. The results of a polyphasic taxonomic study showed that our isolate had characteristics typical of members of the genus Polycladomyces. The isolate grew aerobically at an optimum temperature of 50-55 degrees C and optimal pH 6-7. Meso-diaminopimelic acid was present as the diagnostic diamino acid in the peptidoglycan but no characteristic sugars are detected. The predominant menaquinone was MK-7. The diagnostic phospholipids were phosphatidylethanolamine, phosphatidylmethylethanolamine diphosphatidylglycerol, phosphatidylglycerol and phosphatidylserine. The predominant cellular fatty acid was iso-C-15:0. The DNA G+C content of strain KSR 13(T) was 53.4 mol%. The 16S rRNA gene sequence analysis also indicated that strain KSR 13(T) belonged to the genus Polycladomyces, being most closely related to Polycladomyces abyssicola JIR-001(T) (99.2 %). The DNA-DNA relatedness values that distinguished KSR 13(T) from P. abyssicola JIR-001(T) were 17.8-32.1 %, which were significantly below the 70% cutoff value recommended for species delineation. Following an evaluation of phenotypic, chemotaxonomic and genotypic studies, the new isolate is proposed as a novel species and named Polycladomyces subterraneus sp. nov. The type strain is KSR 13(T) (= BCC 50740(T) = NBRC 109332(T)).
