Halotolerantifilum yawarlongkerapense gen. nov., sp. nov., a novel halotolerant and thermotolerant bacterium isolated from Lake Warden, and proposal of Guggenheimellaceae fam. nov. in the order Peptostreptococcales.

A novel, strictly anaerobic, thermotolerant/halotolerant, heterotrophic bacterial strain, SD5T, was isolated from a brine lake near Esperance, Western Australia. The strain was a non-motile, non-spore-forming, Gram-stain-positive rod. The DNA G+C content was 53.1 mol%, and the length of the closed genome was 3.14 Mbp, with 2,978 protein-encoding genes. 16S rRNA gene sequence identity indicates that the strain is most closely related to Fusibacter fontis KhalAKB1T (89.50% identity). SD5T was phylogenomically distinct from its closest neighbors in the family Acidaminobacteraceae, with percentage of conserved proteins values ranging from 38.74% to 42.66%. The strain grew between 4 and 42 °C (optimum 37 °C), at pH values between 6.5 and 9.0 (optimum 7.0) and with 1-10% (w/v) sodium chloride (optimum 5%). The strain exhibited an aggregated growth phenotype associated with biofilm formation under stress, with cell chains reaching nearly 100 µm in length. The predominant fatty acids were iso-C15:1  ω7c (11.8%), iso-C15:0 (9.3%) and C16:0 (9.3%). Based on phylogenomic and chemotaxonomic analyses, SD5T represents a novel species in a new genus, for which the name Halotolerantifilum yawarlongkerapense gen. nov., sp. nov., is proposed. The type strain is SD5T (=DSM 117693T=ATCC TSD-463T). From this work, we also propose the reassignment of several currently unranked genera within the class Clostridia to families within the order Peptostreptococcales and propose the novel family Guggenheimellaceae fam. nov. based on our sequencing results.