Microbacterium xanthum sp. nov. Isolated from Seaweed, with the Reclassification of Microbacterium ihumii Yacouba et al. 2023 as a Later Heterotypic Synonym of Microbacterium tenebrionis Lee and Kim 2023.

Three actinobacterial strains, designated as KSW-48, KSWW-56 and SSW1-59, were isolated from seawater, rock-attached living and dried seaweeds collected at Gwakji Beach in Jeju, Republic of Korea. All the isolates showed growth at 15-42 °C and pH 5-10, and tolerated NaCl for growth up to 10%. The 16S rRNA gene-based phylogeny showed that the novel strains were closely related with the type strains of Microbacterium aquimaris and Microbacterium luteum, with the 16S rRNA gene sequence similarity of 99.93-100% (0-1 nt differences) with one another and of 99.86-99.93% (1-2 nt differences) with Microbacterium aquimaris KCTC 19124, followed by (98.98-99.04%; 14-15 nt differences) with Microbacterium luteum A18JL200. The core genome-based phylogenomic tree reflected the tree topologies of the 16S rRNA gene-based phylogeny. The chemotaxonomic features were in agreement with the classification in the genus Microbacterium as follow. The cell wall diamino acid and the whole-cell sugars were ornithine. The muramic acid of the cell-wall peptidoglycan was of the N-glycolyl form. The predominant menaquinones were MK-10, MK-11 and MK-12. The polar lipids in common consisted of phosphatidylglycerol and an unidentified glycolipid. The presence of diphosphatidylglycerol and an additional unidentified glycolipid were variable depending on isolated strains. The major fatty acids were anteiso-C, anteiso-C and iso-C. Average nucleotide identity and digital DNA-DNA hybridisation values showed that strain KSW-48 and SSW1-59 represented a new species of the genus Microbacterium, while KSWW-56 was a strain of Microbacterium aquimaris. Based on the results obtained here, Microbacterium xanthum sp. nov. (type strain, SSW1-59 = KCTC 49622 = KACC 23361 = DSM 116382 = MCCC 1K08947) are proposed. Also, it is proposed that Microbacterium ihumii Yacouba et al. 2023 be reclassified as a later heterotypic synonym of Microbacterium tenebrionis Lee and Kim 2023 by high genomic similarity.