Molecular identification of Micromonas (Mamiellales, Mamiellophyceae) strains from Japan maintained in the Microbial Culture Collection at the National Institute for Environmental Studies

Abstract

The genus Micromonas (Mamiellales, Mamiellophyceae) is a eukaryotic picoplankton widely distributed in marine environments. Since the establishment of the genus, only one species, M. pusilla, had been recognized for more than half a century. Recently, M. bravo, M. commoda, and M. polaris were described by detailed electron microscopic observation and molecular phylogeny. On the basis of our molecular analysis, we reidentified 14 Micromonas strains (seven M. pusilla strains and seven unidentified Micromonas strains) from Japan that are maintained in the Microbial Culture Collection at the National Institute for Environmental Studies (Tsukuba, Japan). Our molecular phylogenetic analysis of 18S ribosomal RNA gene confirmed that strains NIES-3661 and NIES-3665 were assigned to M. pusilla. However, strains NIES-1413, NIES-3660, and NIES-3663 were identified as M. bravo, and the other nine strains (NIES-1411, NIES-1412, NIES-2527 to NIES-2530, NIES-3662, NIES-3664, and NIES-4096) belonged to M. commoda. Our results highlight the importance of reidentifying strains in culture collections when the species composition of the genus has been revised by using recent molecular approaches.