Characterization of Streptomyces nymphaeiformis sp. nov., and its taxonomic relatedness to other polyhydroxybutyrate-degrading streptomycetes.

A polyhydroxybutyrate (PHB)-degrading actinomycete, strain SFB5A^T, was identified as a species of Streptomyces based on its membrane fatty acid profile and the presence of ll-diaminopimelic acid in the cell wall. It formed sporulating mycelia on most agar media, but flat or wrinkled, moist colonies on trypticase soy agar. Spores were smooth, cylindrical, and borne on long, straight to flexuous chains. It produced a light brown diffusible pigment, but not melanin. Comparison of genomic digital DNA-DNA hybridization (dDDH) and average nucleotide identity (ANI) values indicated that strain SFB5A^T was related to Streptomyces litmocidini JCM 4394^T, Streptomyces vietnamensis GIMV4.0001^T, Streptomyces nashvillensis JCM 4498^T and Streptomyces tanashiensis JCM 4086^T, plus 11 other species. However, the dDDH and ANI values were well below the species differentiation thresholds of <70 and <95 %, respectively; also, multilocus sequence analysis distances exceeded the species threshold of 0.007. Moreover, strain SFB5A^T differed from the other species in pigmentation and its ability to catabolize arabinose. Strain SFB5A^T and 11 of its 15 closest relatives degraded PHB and have genes for extracellular, short-chain-length denatured polyhydroxyalkanoate depolymerases. These enzymes from strain SFB5A^T and its closest relatives had a type 1 catalytic domain structure, while those from other relatives had a type 2 structure, which differs from type one in the position of a consensus histidine in the active site. Thus, phenotypic and genotypic differences suggest that strain SFB5A^T represents a new species of Streptomyces, for which we propose the name Streptomyces nymphaeiformis sp. nov. The type strain is SFB5A^T (=NRRL B-65520^T=DSM 112030^T).

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