Youngimonas ophiurae sp. nov., a Quorum-Quenching Marine Bacterium Isolated from a Brittle Star in the South China Sea, and Reclassification of Lutimaribacter litoralis as Youngimonas litoralis comb. nov.

Two novel bacterial strains, designated S70^T and S69A, were isolated from a marine brittle star collected in the South China Sea. These strains are Gram-stain-negative, non-motile, aerobic, and rod-shaped. A phylogenomic analysis indicated that strains S70^T and S69A formed a distinct branch with <i>Youngimonas vesicularis</i> CC-AMW-E^T and <i>Lutimaribacter litoralis</i> JCM 17792^T. The DNA G+C content of both strains was 61.5%. The digital DNA-DNA hybridization values with the closest relatives were 21.8, and 21.2%, respectively. Furthermore, the average nucleotide identity (ANIb) values between strain S70^T and these two reference strains were 74.9% and 74.6%, respectively, both well below the 95-96% threshold for dividing prokaryotic species. The major fatty acids of strain S70^T were summed feature 8 (C_18:1<i>ω</i>6<i>c</i> and/or C_18:1<i>ω</i>7<i>c</i>). Functional genomic analysis revealed that strain S70^T possesses potential for hydrocarbon degradation and may play a significant role in sulfur metabolism. Additionally, strain S70^T exhibited broad-spectrum AHL-degrading activity and, most notably, significantly inhibited soft rot caused by <i>Pectobacterium carotovorum</i> in potato tuber assays. Genomic comparisons further support the reclassification of <i>Lutimaribacter litoralis</i> into the genus <i>Youngimonas</i>.