Roseiterribacter gracilis gen. nov., sp. nov., a novel filterable alphaproteobacterium isolated from soil using a gel-filled microwell array device

by Ryosuke Nakai, Hiroyuki Kusada, Fumihiro Sassa, Ayaka Makino, Susumu Morigasaki, Hisayoshi Hayashi, Naoki Takaya, Hideyuki Tamaki

Our previous studies indicate the abundant and diverse presence of yet-to-be-cultured microorganisms in the micropore-filtered fractions of various environmental samples. Here, we isolated a novel bacterium (designated as strain TMPK1^T) from a 0.45-μm-filtered soil suspension by using a gel-filled microwell array device comprising 900 microwells and characterized its phylogenetic and physiological features. This strain showed low 16S rRNA gene sequence identities (<91%) and low average nucleotide identity values (<70%) to the closest validly described species, and belonged to a novel-family-level lineage within the order Rhodospirillales of Alphaproteobacteria. Strain TMPK1^T exhibited small cell sizes (0.08–0.23 μm³) and had a high cyclopropane fatty acid content (>13%), and these characteristics were differentiated from other Rhodospirillales bacteria. A comprehensive habitability search using amplicon datasets suggested that TMPK1^T and its close relatives are mainly distributed in soil and plant-associated environments. Based on these results, we propose that strain TMPK1^T represents a novel genus and species named Roseiterribacter gracilis gen. nov., sp. nov. (JCM 34627^T = KCTC 82790^T). We also propose Roseiterribacteraceae fam. nov. to accommodate the genus Roseiterribacter.