Lacipirellula parvula gen. nov., sp. nov., representing a lineage of planctomycetes widespread in low-oxygen habitats, description of the family Lacipirellulaceae fam. nov. and proposal of the orders Pirellulales ord. nov., Gemmatales ord. nov. and Isosphaerales ord. nov.

Pirellula-like planctomycetes are ubiquitous aquatic bacteria, which are often detected in anoxic or microoxic habitats. By contrast, the taxonomically described representatives of these bacteria, with very few exceptions, are strict aerobes. Here, we report the isolation and characterization of the facultatively anaerobic planctomycete, strain PX69(T), which was isolated from a boreal lake. Its 16S rRNA gene sequence is affiliated with the Pirellula-related Pir4 Glade, which is dominated by environmental sequences retrieved from a variety of low-oxygen habitats. Strain PX69(T) was represented by ellipsoidal cells that multiplied by budding and grew on sugars, some polysaccharides and glycerol. Anaerobic growth occurred by means of fermentation. Strain PX69(T) grew at pH 5.5-7.5 and at temperatures between 10 and 30 degrees C. The major fatty acids were C18:1 omega 9c, C16:0 and C16:1 omega 7c; the major intact polar lipid was dimethylphosphatidylethanolamine. The complete genome of strain PX69(T) was 6.92 Mb in size; DNA G + C content was 61.7 mol%. Among characterized planctomycetes, the highest 16S rRNA gene similarity (90.4%) was observed with Bythopirellula goksoyri' Prld, a planctomycete from deep-sea sediments. We propose to classify PX69T as a novel genus and species, Lacipirellula parvula gen. nov., sp. nov.; the type strain is strain PX69(T) (=KCTC 72398(T) = CECT 9826(T) = VKM B-3335(T)). This genus is placed in a novel family, Lacipirellulaceae fam. nov., which belongs to the order Pirellulales ord. nov. Based on the results of comparative genome analysis, we also suggest establishment of the orders Gemmatales ord. nov. and Isosphaerales ord. nov. as well as an emendation of the order Planctomycetales. (C) 2019 The Authors. Published by Elsevier GmbH.