Description of three new Leptotrichia species isolated from dental biofilm: Leptotrichia rugosa sp. nov., Leptotrichia mesophila sp. nov. and Leptotrichia alba sp. nov.

Three bacterial strains, namely HSP-334, HSP-342 and HSP-536, were isolated from human oral dental biofilm. These strains were identified as Gram-stain-negative, straight or slightly curved anaerobes. Based on 16S rRNA genes analysis, strain HSP-334 exhibited the closest identity to Leptotrichia shahii LB37 (92.25%). Strain HSP-342 demonstrated the highest similarity to Leptotrichia hongkongensis HKU24 (98.03%), while strain HSP-536 displayed the greatest resemblance to Leptotrichia buccalis DSM 1135 (97.77%). Notably, the maximum sequence similarity among the three isolates ranged from 91.56% to 94.12%. All the phylogenies showed that strains HSP-334, HSP-342, HSP-536, all members of genus Leptotrichia and Pseudoleptotrichia goodfellowii JCM 16774 were clustered in one subclade within the family Leptotrichiaceae. The average nucleotide identity (ANI) and digital DNA-DNA hybridization (dDDH) values calculated between these three strains and their phylogenetically related species were determined to be lower than the established species delineation threshold values. The major cellular fatty acids detected in these novel strains were C and Cω7c. Strains HSP-334, HSP-342 and HSP-536 could be distinguished from each other by several phenotypic characteristics. Based on the comprehensive polyphasic taxonomic characterizations conducted, strains HSP-334, HSP-342 and HSP-536 represent three novel species of the genus Leptotrichia, for which the name Leptotrichia rugosa sp. nov. (type strain HSP-334 = JCM 36566 = CGMCC 1.18095 = MCCC 1K09354), Leptotrichia mesophila sp. nov. (type strain HSP-342 = JCM 36567 = CGMCC 1.18052 = MCCC 1K09338) and Leptotrichia alba sp. nov. (type strain HSP-536 = JCM 36662 = CGMCC 1.18096 = MCCC 1K09339) are proposed.