Isolation and characterization of Polaribacter sargassicola sp. nov. and Algibacter ulvanivorans sp. nov.: two novel species with ability to degrade algal polysaccharides

Abstract

The genera Polaribacter and Algibacter, which are members of the Bacteroidota family Flavobacteriaceae, are well known for their arsenal of carbohydrate-active enzymes (CAZymes) and specialized polysaccharide utilization loci (PULs). In this study, two aerobic, gram-negative, and rod-shaped bacterial strains, designated strains DS7-9 ^T and PT7-4 ^T, were isolated from the surface of seaweed collected from the coastal zone of Fujian Province, China. The two strains exhibited broad tolerance ranges to salinity (0–4%), temperature (10–40 °C) and pH (5.0–10.0). The predominant fatty acids in strain DS7-9 ^T were iso-C_15:0 (53.7%) and iso-C_15:0 3-OH (10.9%), whereas those in strain PT7-4 ^T were iso-G-C_15:1 (33.2%) and iso-C_15:0 (27.1%). Additionally, the predominant menaquinone was MK-6. The 16S rRNA gene of strain DS7-9 ^T shares 97.5% similarity with that of Polaribacter haliotis KCTC 52418 ^T, whereas that of strain PT7-4 ^T is 97.0% sequence similarity with that of Algibacter mikhailovii KCTC 12710 ^T. Phylogenomic analysis revealed that the highest average nucleotide identity (ANI) value between strain DS7-9 ^T and its closest relative reached 84.7%, whereas the corresponding value for strain PT7-4 ^T was 84.2%. Genomic characterization revealed DNA G + C contents of 29.5% and 31.9% for strains DS7-9 ^T and PT7-4 ^T, respectively. Both strains possessed complete circular chromosomes, with genome sizes of 3.7 Mb (DS7-9 ^T) and 3.5 Mb (PT7-4 ^T). Bioinformatic analysis revealed that strain DS7-9 ^T harbors 5 PULs putatively associated with laminarin, ulvan, fucoidan, and alginate catabolism, whereas strain PT7-4 ^T possesses 7 PULs predicted to target ulvan, alginate, and starch metabolism. On the basis of their distinct physiological characteristics, two strains are suggested for classification into novel species: Polaribacter sargassicola sp. nov. (type strain DS7-9 ^T = MCCC 1K08670^T = KCTC 102076 ^T) and Algibacter ulvanivorans sp. nov. (type strain PT7-4 ^T = MCCC 1K08669^T = KCTC 102077 ^T).