Two Novel Ferruginibacter Species from Freshwater Sediments and a Putative Class I Lanthipeptide Biosynthetic Gene Cluster of SUN106T

Freshwater sediments harbor taxonomically diverse and biosynthetically underexplored bacteria. In this study, two orange-pigmented strains, SUN002ᵀ and SUN106ᵀ, isolated from freshwater sediments in South Korea, were characterized using a polyphasic taxonomic approach. Phylogenetic, phenotypic, chemotaxonomic, and genome-based analyses supported their classification as two novel species within the genus Ferruginibacter, for which the names Ferruginibacter aquae sp. nov. and Ferruginibacter aurantiacus sp. nov. are proposed, respectively. The highest average nucleotide identity and digital DNA–DNA hybridization values obtained against established Ferruginibacter species were 87.3% and 33.7%, respectively, both below the accepted species delineation thresholds. Genome mining identified a putative class I lanthipeptide biosynthetic gene cluster in SUN106ᵀ containing lanB, lanC, and lanT, together with eight adjacent candidate LanA-like precursor ORFs. The predicted core regions were rich in Ser, Thr, and Cys residues and were computationally predicted to support multiple thioether crosslinks. Crude extracts of SUN106ᵀ showed inhibitory activity against Bacillus subtilis; however, targeted UPLC–QTOF–MS analysis of the culture-supernatant, cell-bound, and lysate fractions did not detect convincing evidence of the predicted mature or precursor-related products. The observed antibacterial activity cannot currently be attributed to the putative BGC. Together, these findings expand the recognized taxonomic and biosynthetic diversity of the genus Ferruginibacter and provide a genomic foundation for future functional characterization of cryptic class I lanthipeptide biosynthesis in freshwater bacteria.