Polynucleobacter aenigmaticus sp. nov. isolated from the permanently anoxic monimolimnion of a temperate meromictic lake

The bacterial strain MWH-K35W1T was isolated from a permanently anoxic water layer of a meromictic lake located in the Austrian Salzkammergut area. The basically chemo-organoheterotrophic strain was isolated and maintained under aerobic conditions. Phylogenetic analyses of the 16S rRNA gene and the glutamine synthetase gene (glnA) of the strain suggested an affiliation to the genus Polynucleobacter and the cryptic species complex PnecC. Strain MWH-K35W1T shares with the type strains of the six free-living species of the genus Polynucleobacter affiliated with this species complex 16S rRNA gene sequence similarities of 99.6–99.9 %, while the type material of the obligate endosymbiont Polynucleobacter necessarius, which is also affiliated with this species complex, shares a gene sequence similarity of 99.1 %. Genome sequencing resulted in a genome size of 2.14 Mbp and a DNA G+C content of 45.98 mol%. Major fatty acids were C16 : 1ω7c, C18 : 1ω7c and C16 : 0. This strain is the first strain of the genus Polynucleobacter found to encode a proteorhodopsin-like protein but, in contrast to some other strains affiliated to this genus, it does not encode a putative anoxygenic photosynthesis system. Multilocus sequence analysis based on partial sequences of eight housekeeping genes, as well as average nucleotide identity (ANI) analyses, did not suggest that strain MWH-K35W1T belongs to a previously described species. We propose the name Polynucleobacter aenigmaticus for a novel species with strain MWH-K35W1T (=DSM 24006T=LMG 29706T) as the type strain.