Summary auto-generated
This study describes the isolation and characterization of a novel actinomycete, strain IM 7744T, recovered from soil in Singapore's tropical rainforest. The organism exhibits highly pleomorphic morphology, transitioning from irregular squarish cells and short chains in early growth to branched hyphae with uneven thickness during prolonged cultivation. The strain is notably salt-tolerant, growing in up to 15% NaCl. Chemotaxonomic analysis revealed LL-diaminopimelic acid 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, though it shared only 90.6-91.2% sequence similarity with the closest relatives, Kribbella species. Based on polyphasic evidence including unique morphological features, distinctive chemotaxonomic profile, and phylogenetic position separated by a long branch from related genera, the authors propose a new genus and species: Actinopolymorpha singaporensis gen. nov., sp. nov. The DNA G+C content is 69.5 mol%.
Key findings
- A novel actinomycete strain IM 7744T with highly pleomorphic cell morphology was isolated from Singapore tropical rainforest soil
- The organism exhibits exceptional salt tolerance, growing in media containing up to 15% NaCl
- 16S rDNA sequence similarity to known actinomycetes was very low (≤91.2%), indicating a distant phylogenetic relationship despite family Nocardioidaceae assignment
- Chemotaxonomic characterization identified distinctive features including MK-9(H6) as predominant menaquinone and type PI phospholipids
- Polyphasic evidence supported designation of a new genus and species, Actinopolymorpha singaporensis
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Abstract
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(H(6)) 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.