Actinopolymorpha singaporensis gen. nov., sp. nov., a novel actinomycete from the tropical rainforest of Singapore.

A novel actinomycete was isolated from soil in the tropical rainforest of Singapore. The cells of this actinomycete are highly pleomorphic. In the early stages of growth, most cells are of irregular squarish shape and varied sizes. Cells remain attached after cell division, often forming chains or aggregates of a few cells. Cells at the end of a chain tend to elongate. With prolonged cultivation, cells show different degrees of elongation and enlargement, producing branched hyphae of uneven thickness. At the periphery of the colony, long hyphae form, which are divided into alternating segments of elongated cells and chains of squarish cells. This actinomycete is considerably salt-tolerant, able to grow in the presence of 15% NaCl. Chemotaxonomically, it contains LL-diaminopimelic acid (DAP) in the cell wall, type PI phospholipids and MK-9(H6) as the predominant menaquinone. 16S rDNA sequence analysis assigned this actinomycete to the family Nocardioidaceae, but its 16S rDNA shared no more than 91.2% sequence similarity with other members of the family. Based on phenotypic, chemotaxonomic and phylogenetic evidence, it is proposed that this actinomycete be classified as a new species in a new genus, Actinopolymorpha singaporensis gen. nov., sp. nov.