Altererythrobacter guangdongensis sp. nov. and Tsuneonella sediminis sp. nov., two novel carotenoid-producing species isolated from tidal flat sediment.

Four aerobic, Gram-stain-negative, rod-shaped, and non-motile bacterial strains, designated SYSU HZ0097ᵀ, SYSU HZ0136, SYSU LHT278ᵀ, and SYSU LHT272, were isolated from tidal flat sediment collected in Zhuhai, China. Phylogenetic analysis based on 16S rRNA gene sequences assigned all four strains to the family Erythrobacteraceae. Strains SYSU HZ0097ᵀ and SYSU HZ0136 showed the highest 16S rRNA gene sequence similarity (98.6 %) to Altererythrobacter epoxidivorans CGMCC 1.7731ᵀ, while SYSU LHT278ᵀ and SYSU LHT272 were most closely related (98.5 %) to Tsuneonella litorea KCTC 82812ᵀ. Whole-genome comparisons, including average nucleotide identity (ANI < 85.0 %) and digital DNA-DNA hybridization (dDDH <30.0 %), supported their assignment to two distinct species. All isolates contained ubiquinone-10 (Q-10) as the predominant respiratory quinone, and the major fatty acids (>10 %) were Cω7c and Cω6c. The polar lipid profiles included phosphatidylglycerol, phosphatidylethanolamine, and an unidentified glycolipid. The colonies exhibited yellow pigmentation, and genes associated with carotenoid biosynthesis (crtB, crtI) were identified in their genomes. Based on phylogenetic, genomic, phenotypic, and chemotaxonomic characteristics, strains SYSU HZ0097ᵀ and SYSU HZ0136 represent a new species of the genus Altererythrobacter, for which the name Altererythrobacter guangdongensis sp. nov. is proposed (type strain SYSU HZ0097ᵀ = MCCC 1K09423ᵀ = KCTC 8714ᵀ). Strains SYSU LHT278ᵀ and SYSU LHT272 represent a new species of the genus Tsuneonella, for which the name Tsuneonella sediminis sp. nov. is proposed (type strain SYSU LHT278ᵀ = MCCC 1K09543ᵀ = KCTC 8862ᵀ).