Anaerobaca lacustris gen. nov., sp. nov., an obligately anaerobic planctomycete of the widespread SG8-4 group, isolated from a coastal lake, and proposal of Anaerobacaceae fam. nov

One of the numerous and widespread lineages of planctomycetes is the hitherto uncultured SG8-4 group inhabiting anoxic environments. A novel anaerobic, mesophilic, alkalitolerant, chemoorganotrophic bacterium (strain M17dextr^T) was isolated from anaerobic sediment of a coastal lake (Taman Peninsula, Russia). The cell were mainly non-motile cocci, 0.3 to 1.0 µm in diameter forming chains or aggregates. The cells had a Gram-negative cell wall and divided by binary fission. The temperature range for growth was 20–37 ⁰C (optimum at 30 ⁰C). The pH range for growth was 6.5–10.0, with an optimum at pH 8.0–8.5. Strain M17dextr^T fermented mono-, di- and polysaccharides (starch, xanthan gum, dextran, N-acetylglucosamine), but did not utilized proteinaceous compounds. Major cellular fatty acids were C_16:0 and C_18:0. The genome of strain M17dextr^T had a size of 5.7 Mb with a G + C content of 62.49 %. The genome contained 345 CAZyme genes. The closest cultured phylogenetic relatives of strain M17dextr^T were members of the order Sedimentisphaerales, class Phycisphaerae. Among characterized planctomycetes, the highest 16S rRNA gene sequence similarity (88.3 %) was observed with Anaerohalosphaera lusitana. According to phylogenomic analysis strain M17dextr^T together with many uncultured representatives of Sedimentisphaerales forms a separate family‐level lineage. We propose to assign strain M17dextr^T to a novel genus and species, Anaerobaca lacustris gen. nov., sp. nov.; the type strain is M17dextr^T (=VKM B-3571 ^T = DSM 113417 ^T = JCM 39238 ^T = KCTC 25381 ^T = UQM 41474 ^T). This genus is placed in a novel family, Anaerobacaceae fam. nov. within the order Sedimentisphaerales.