sp. nov., a non-photosynthetic bacterium adjusting its metabolism to the diurnal light cycle and reclassification of as gen. nov., comb. nov.

The aerobic primarily chemoorganotrophic actinobacterial strain MWH-Mo1 was isolated from a freshwater lake and is characterized by small cell lengths of less than 1 µm, small cell volumes of 0.05-0.06 µm (ultramicrobacterium), a small genome size of 1.75 Mbp and, at least for an actinobacterium, a low DNA G+C content of 54.6 mol%. Phylogenetic analyses based on concatenated amino acid sequences of 116 housekeeping genes suggested the type strain of affiliated with the family as its closest described relative. Strain MWH-Mo1 shares with the type strain of that species a 16S rRNA gene sequence similarity of 99.6 % but the genomes of the two strains share an average nucleotide identity of only 79.3 %. Strain MWH-Mo1 is in many genomic, phenotypic and chemotaxonomic characteristics quite similar to the type strain of . Previous intensive investigations revealed two unusual traits of strain MWH-Mo1. Although the strain is not known to be phototrophic, the metabolism is adjusted to the diurnal light cycle by up- and down-regulation of genes in light and darkness. This results in faster growth in the presence of light. Additionally, a cell size-independent protection against predation by bacterivorous flagellates, most likely mediated by a proteinaceous cell surface structure, was demonstrated. For the previously intensively investigated aerobic chemoorganotrophic actinobacterial strain MWH-Mo1 (=CCUG 56426=DSM 107758), the establishment of the new species sp. nov. is proposed.