Genome Analysis and Characterization of Formosa bonchosmolovskayae sp. nov. Isolated from Brown and Green Algae, and a Proposal to Reclassify Formosa maritima Cao et al. 2020 and Bizionia arctica Li et al. 2015 as Xanthomarina New Members

Two marine bacteria, designated strains 4Alg 33^Tand 3Alg 14/1, were isolated from brown (<i>Saccharina japonica</i>) and green (<i>Ulva fenestrata</i>) macroalgae, respectively. These isolates were aerobic Gram-negative rods exhibiting a gliding motility. The 16S rRNA gene phylogenetic analysis clearly showed their belonging to the genus <i>Formosa</i>, the family <i>Flavobacteriaceae</i>, and the phylum <i>Bacteroidota</i>. The closest relatives of the new strains were <i>Formosa undariae</i> KCTC 32328^T (99.05%), <i>Formosa arctica</i> IMCC 9485^T (99.05%) and <i>Formosa agariphila</i> KMM 3901^T (98.96%). The ANI and dDDH values between the two new strains were 97.9% and 85.3%, respectively. The AAI values between 4Alg 33^T and <i>Formosa</i> type strains ranged from 80.1% (<i>Formosa haliotis</i> MA1^T) to 91.4% (<i>F. undariae</i> KCTC 32328^T). The cellular fatty acid and polar lipid profiles of the new isolates were generally similar to those of the type strains of <i>Formosa</i> species. The genomes of 4Alg 33^T and 3Alg 14/1 are represented by a circular chromosome of 4,157,724 bp and 4,316,096 bp in size with 3536 and 3879 protein-coding genes, respectively. They shared a DNA G+C content of 34.3 mol% and comprised four <i>rrn</i> operons. The pangenome of the genus <i>Formosa</i> belongs to the open type and is characterized by an abundance of CAZymes. The proportion of CAZyme genes in novel genomes was more than 5%, with a prevalence of glycoside hydrolase genes, suggesting great potential for utilizing marine-derived polysaccharides. Based on the results of polyphasic characterization, the two algal isolates represent a distinct species lineage within the genus <i>Formosa</i>, for which we propose the name <i>Formosa bonchosmolovskayae</i> sp. nov. with the type strain 4Alg 33^T (= KMM 3963^T = KCTC 72008^T). In addition, we have proposed to transfer <i>Formosa maritima</i> Cao et al. 2020 and <i>Bizionia arctica</i> Li et al. 2015 to the genus <i>Xanthomarina</i> Vaidya et al. 2015 as <i>Xanthomarina maritima</i> comb. nov. and <i>Xanthomarina arctica</i> comb. nov. based on a combination of the genomic and phenotypic characteristics.