| Abstract |
Three strains of actinobacteria, designated as B-S-A6T, B-S-A8T and B-S-A12T, were isolated from soil samples collected in the Phu Pha Phet Cave located in the Satun UNESCO Global Geopark, Satun Province, Thailand. A comprehensive polyphasic approach was used to describe these strains. Strains B-S-A6T, B-S-A8T and B-S-A12T were identified within the genus Streptomyces based on a comparative examination of 16S rRNA gene sequences. Strains B-S-A8T and B-S-A12T showed a high genetic similarity to Streptomyces spectabilis NBRC 13424T (99.0%, for both) and to Streptomyces deserti C63T (98.6 and 98.7 %, respectively). Meanwhile, strain B-S-A6T exhibited 98.6% sequence similarity with S. spectabilis NBRC 13424T and Streptomyces koyangensis VK-A6 T. However, upon further comparison, the 16S rRNA gene sequence of strain B-S-A6T showed a similarity of 99.6% to B-S-A8T and 99.7% to B-S-A12T. Contrastingly, B-S-A8T showed a very high similarity of 99.8% with B-S-A12T. The use of digital DNA-DNA hybridization, along with the analysis of average nt identities and aa identities, comparing the three strains to their closest known type strains, validated that each of these strains represents a new and distinct species. Three newly identified strains exhibited phenotypic characteristics and chemotaxonomic properties consistent with the members of the genus Streptomyces. The primary menaquinones identified in these strains were MK-9(H6) and MK-9(H8). The major fatty acids were iso-C15 : 0 and anteiso-C15 : 0. Their polar lipid profiles included diphosphatidylglycerol, phosphatidylethanolamine, hydroxy-phosphatidylethanolamine, phosphatidylinositol and phosphatidylinositol mannoside. The comprehensive phenotypic and genomic analyses of the Streptomyces strains strongly suggest that strains B-S-A6T, B-S-A8T and B-S-A12T represent three new species for which the names Streptomyces cavernicola sp. nov. (type strain B-S-A6T =TBRC 17074T =NBRC 116118T), Streptomyces solicavernae sp. nov. (type strain B-S-A8T =TBRC 17072T =NBRC 116117T) and Streptomyces luteolus sp. nov. (type strain B-S-A12T =TBRC 17060T =NBRC 116116T) are proposed.
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