Lactic acid production of bacteria from tree barks and proposal of Sporolactobacillus caesalpiniae sp. nov.

Lactic acid bacteria are widely exploited in biotechnology due to their fermentation capacity and metabolite production. In this study, 19 isolates were recovered from tree bark collected across Thailand, representing the genera <i>Enterococcus</i> (11 isolates), <i>Lactococcus</i> (2 isolates), <i>Weizmannia</i> (3 isolates), <i>Sporolactobacillus</i> (2 isolates) and <i>Terrilactibacillus</i> (1 isolate). All exhibited homofermentative metabolism, producing l-, dl- or d-lactic acid. Among them, strain STCC-11^T, isolated from the bark of <i>Caesalpinia coriaria</i> in Satun Province, Thailand, demonstrated strong potential for d-lactic acid production, achieving 96.31% optical purity, 1.082 g l^-1 concentration and 0.451 g g^-1 glucose yield. This novel Gram-positive, spore-forming, facultatively anaerobic bacterium STCC-11^T grew at 30-45 °C, pH 6.0-9.0 and up to 3% NaCl. Phylogenetic analysis of the 16S rRNA gene revealed 99.71% similarity with <i>Sporolactobacillus nakayamae</i> subsp. <i>nakayamae</i> ATCC 700379^T. In addition, whole-genome analyses indicated that STCC-11^T is distinct, with average nucleotide identity based on BLAST (ANIb) (94.12%), average nucleotide identity based on MUMmer (ANIm) (95.29%) and digital DNA-DNA hybridization (dDDH) (60.3%) values below species delineation thresholds. The genome (3.57 Mb, 43.8% G+C) encodes both <i>ldhD</i> and <i>ldhL</i> genes, and <i>in silico</i> safety assessment confirmed the absence of pathogenicity or transferable resistance genes. Based on polyphasic taxonomic evidence, STCC-11^T represents a novel species of the genus <i>Sporolactobacillus</i>, for which the name S<i>porolactobacillus caesalpiniae</i> sp. nov. is proposed. The type strain is STCC-11^T (LMG 33980^T <b>=</b>TISTR 10806^T).