Lentimicrobium saccharophilum gen. nov., sp nov., a strictly anaerobic bacterium representing a new family in the phylum Bacteroidetes, and proposal of Lentimicrobiaceae fam. nov.

A novel, strictly anaerobic, short rod-shaped bacterium, designated strain TBC1(T), was isolated from methanogenic granular sludge in a full-scale mesophilic upflow anaerobic sludge blanket reactor treating high-strength starch-based organic wastewater. Cells of this strain were 2-4 mu m long and 0.4-0.6 mu m wide. They were non-motile and Gram-stain-negative. The optimum growth temperature was 30-37 degrees C, with a range of 20-40 degrees C. The optimum pH for growth was around pH 7.0, while growth occurred in a range of pH 6.5-9.0. Strain TBC1(T) grew chemoorganotrophically on a narrow range of carbohydrates under anaerobic conditions. Yeast extract was required for its growth. The major fermentative end products from glucose, supplemented with yeast extract, were acetate, malate, propionate, formate and hydrogen. Doubling time under optimal growth conditions was estimated to be 1 day. The DNA G+C content of strain TBC1(T) was 49.2 mol% as determined by HPLC. Major cellular fatty acids were C-16:0, C-18:0, C-16:1 omega 9c and C-18:1 omega 9c. Based on its 16S rRNA gene sequence, strain TBC1(T) was shown to represent a distinct lineage at the family level in the phylum Bacteroidetes. Among previously described species of this phylum, Mucilaginibacter boryungensis BDR-9(T) (Sphingobacteriaceae) displayed the highest sequence similarity (85.9%) with strain TBC1(T). Phylogenomic analyses using 38-83 single copy marker genes also supported the novelty of strain TBC1(T) at the family level. Based on its characteristics, strain TBC1(T) (=JCM 30898(T)=DSM 100618(T)) is considered to be the type strain of a novel species of a new genus, Lentimicrobium saccharophilum gen. nov., sp. nov. A new family, Lentimicrobiaceae fam. nov., is also proposed encompassing the strain and related environmental 16S rRNA gene clone sequences.