Three bacterial strains, namely HSP-334T, HSP-342T and HSP-536T, 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-334T exhibited the closest identity to Leptotrichia shahii LB37T (92.25 %). Strain HSP-342T demonstrated the highest similarity to Leptotrichia hongkongensis HKU24T (98.03 %), while strain HSP-536T displayed the greatest resemblance to Leptotrichia buccalis DSM 1135T (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-334T, HSP-342T, HSP-536T, all members of genus Leptotrichia and Pseudoleptotrichia goodfellowii JCM 16774T 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 C16:0 and C18:1ω7c. Strains HSP-334T, HSP-342T and HSP-536T could be distinguished from each other by several phenotypic characteristics. Based on the comprehensive polyphasic taxonomic characterizations conducted, strains HSP-334T, HSP-342T and HSP-536T represent three novel species of the genus Leptotrichia, for which the name Leptotrichia rugosa sp. nov. (type strain HSP-334T = JCM 36566T = CGMCC 1.18095T = MCCC 1K09354T), Leptotrichia mesophila sp. nov. (type strain HSP-342T = JCM 36567T = CGMCC 1.18052T = MCCC 1K09338T) and Leptotrichia alba sp. nov. (type strain HSP-536T = JCM 36662T = CGMCC 1.18096T = MCCC 1K09339T) are proposed.
Keywords: Dental biofilm; Leptotrichia; Leptotrichia alba; Leptotrichia mesophila; Leptotrichia rugosa; Polyphasic taxonomy.
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