Limnoglobus roseus gen. nov., sp. nov., a novel freshwater planctomycete with a giant genome from the family Gemmataceae

Abstract

The family <i>Gemmataceae</i> accommodates aerobic, chemoorganotrophic planctomycetes, which inhabit various freshwater ecosystems, wetlands and soils. Here, we describe a novel member of this family, strain PX52^T, which was isolated from a boreal eutrophic lake in Northern Russia. This isolate formed pink-pigmented colonies and was represented by spherical cells that occurred singly, in pairs or aggregates and multiplied by budding. Daughter cells were highly motile. PX52^T was an obligate aerobic chemoorganotroph, which utilized various sugars and some heteropolysaccharides. Growth occurred at pH 5.0-7.5 (optimum pH 6.5) and at temperatures between 10 and 30 °C (optimum 20-25 °C). The major fatty acids were C_{18 : 1}ɷ7c, C_{18 : 0} and βOH-C_16:0; the major intact polar lipid was trimethylornithine, and the quinone was MK-6. The complete genome of PX52^T was 9.38 Mb in size and contained nearly 8000 potential protein-coding genes. Among those were genes encoding a wide repertoire of carbohydrate-active enzymes (CAZymes) including 33 glycoside hydrolases (GH) and 87 glycosyltransferases (GT) affiliated with 17 and 12 CAZy families, respectively. DNA G+C content was 65.6 mol%. PX52^T displayed only 86.0-89.8 % 16S rRNA gene sequence similarity to taxonomically described <i>Gemmataceae</i> planctomycetes and differed from them by a number of phenotypic characteristics and by fatty acid composition. We, therefore, propose to classify it as representing a novel genus and species, <i>Limnoglobus roseus</i> gen. nov., sp. nov. The type strain is strain PX52^T (=KCTC 72397^T=VKM B-3275^T).