Christiangramia qingdaonensis sp. nov., a novel polysaccharide-degrading Bacteroidota bacterium, isolated from intertidal sediment

A novel polysaccharide-degrading bacterial strain, designated ASW11-125 ^T , was isolated from intertidal sediments in Aoshan Bay, Qingdao, China. The strain was strictly aerobic, Gram-stain-negative, catalase-positive but oxidase-negative, short rod-shaped, and exhibited gliding motility without flagella. Growth occurred at 4–35°C (optimum 28°C), pH 6.0–8.0 (optimum pH 7.0), and in 0.5–16.0% NaCl (optimum 2.5–3.0%). The predominant polar lipid was phosphatidylethanolamine. Major fatty acids were iso-C _15:0 and iso-C _17:0 3-OH, and the primary respiratory quinone was menaquinone-6 (MK-6). Based on the phylogenetic analyses of 16S rRNA gene sequences and 1542 single copy orthologous clusters, strain ASW11-125 ^T affiliated with the genus Christiangramia and was closely related to Christiangramia portivictoriae MCCC 1A00585 ^T (98.8%), Christiangramia aquimixticola KCTC 42706 ^T (98.8%) and Christiangramia marina KCTC 12366 ^T (98.6%). Comparative genomic analysis revealed that the average nucleotide identity (ANI) and digital DNA–DNA hybridization (dDDH) values between strain ASW11-125ᵀ and its closely related species (74.6–91.5% and 18.6–44.3%, respectively) were clearly lower than the proposed species cutoff values. Based on a polyphasic characterization integrating phenotypic, phylogenetic, and chemotaxonomic evidence, strain ASW11-125ᵀ represents a novel species of the genus Christiangramia , for which the name Christiangramia qingdaonensis sp. nov. is proposed. The draft genome of strain ASW11-125ᵀ is 3.2 Mb in size with a G + C content of 38.3%. Notably, genomic analysis revealed an abundance of genes encoding putative carbohydrate-active enzymes (CAZymes), particularly those associated with starch, laminarin, and fructan utilization, suggesting its potential role in the marine carbon cycle. The type strain is ASW11-125ᵀ (= KCTC 102340ᵀ = MCCC 1K09555ᵀ).