Actinomadura terrae sp. nov. and Actinomadura litoris OS3-89, isolated from rhizosphere soil of cactus

Abstract

Two mycelium-forming actinobacterial strains, designated OS3-83T and OS3-89, were isolated from rhizosphere soil of a cactus (Opuntia ficus-indica) sampled on Mara Island, Jeju, Republic of Korea. Both of the isolates were found to grow at 20？37 °C, pH 6.0？10.0 and with 0？2% (w/v) NaCl. Their taxonomic positions were investigated by a polyphasic approach. Strains OS3-83T and OS3-89 were most closely related to the type strain of Actinomadura litoris (99.5% and 98.9% 16S rRNA gene sequence similarity, respectively). Both of the isolates shared 99.2% sequence similarity to each other. Morphological and chemotaxonomic characteristics supported the affiliation of the two isolates to the genus Actinomadura. 16S rRNA gene phylogeny exhibited that strain OS3-83T formed a tight cluster with A. litoris, while strain OS3-89 occupied a position located remotely from A. litoris. Nevertheless, phylogenomic analysis based on 92 core gene sequences showed that both of the isolates formed a tight clade with A. litoris. The values of average nucleotide identity and digital DNA？DNA hybridization between strain OS3-83T and the closest relative, A. litoris, were 92.2 and 46.2%, respectively, whereas strain OS3-89 shared an average nucleotide identity value of 97.5% and a digital DNA？DNA hybridization value of 76.9% with A. litoris. These results strongly suggested that strain OS3-83T (=KACC 19752T=NBRC 114688T) represents a novel species and strain OS3-89 (=KACC 19753=NBRC 114400) is a strain of A. litoris. On the basis of the data obtained here, strain OS3-83T is considered to represent a new species of the genus Actinomadura, for which the name Actinomadura terrae sp. nov. is proposed.