In recent years, marine macroalgae with extensive biomass have attracted the attention of researchers worldwide. Furthermore, algal polysaccharides have been widely studied in the food, pharmaceutical, and cosmetic fields because of their various kinds of bioactivities. However, there are immense barriers to their application as a result of their high molecular size, poor solubility, hydrocolloid nature, and low physiological activities. Unique polysaccharides, such as laminarin, alginate, fucoidan, agar, carrageenan, porphyran, ulvan, and other complex structural polysaccharides, can be digested by marine bacteria with many carbohydrate-active enzymes (CAZymes) by breaking down the limitation of glycosidic bonds. However, structural elucidation of algal polysaccharides, metabolic pathways, and identification of potential polysaccharide hydrolases that participate in different metabolic pathways remain major obstacles restricting the efficient utilization of algal oligosaccharides. This review focuses on the structure, hydrolase families, metabolic pathways, and potential applications of seven macroalgae polysaccharides. These results will contribute to progressing our understanding of the structure of algal polysaccharides and their metabolic pathways and will be valuable for clearing the way for the compelling utilization of bioactive oligosaccharides.
The genus
Tamlana
from the
Bacteroidota
currently includes six validated species. Two strains designated PT2-4T and 62-3T were isolated from Sargassum abundant at the Pingtan island coast in the Fujian Province of China. 16S rRNA gene sequence analysis showed that the closest described relative of strains PT2-4T and 62-3T is
Tamlana sedimentorum
JCM 19808T with 98.40 and 97.98% sequence similarity, respectively. The 16S rRNA gene sequence similarity between strain PT2-4T and strain 62-3T was 98.68 %. Furthermore, the highest average nucleotide identity values were 87.34 and 88.97 % for strains PT2-4T and 62-3T, respectively. The highest DNA–DNA hybridization (DDH) value of strain PT2-4T was 35.2 % with strain 62-3T, while the DDH value of strain 62-3T was 37.7 % with
T. sedimentorum
JCM 19808T. Growth of strains PT2-4T and 62-3T occurs at 15–40 °C (optimum, 30 °C) with 0–4 % (w/v) NaCl (optimum 0–1 %). Strains PT2-4T and 62-3T can grow from pH 5.0 to 10.0 (optimum, pH 7.0). The major fatty acids of strains PT2-4T and 62-3T are iso-C15 : 0 and iso G-C15 : 1. MK-6 is the sole respiratory quinone. Genomic and physiological analyses of strains PT2-4T and 62-3T showed corresponding adaptive features. Significant adaptation to the growth environment of macroalgae includes the degradation of brown algae-derived diverse polysaccharides (alginate, laminarin and fucoidan). Notably, strain PT2-4T can utilize laminarin, fucoidan and alginate via specific carbohydrate-active enzymes encoded in polysaccharide utilization loci, rarely described for the genus
Tamlana
to date. Based on their distinct physiological characteristics and the traits of utilizing polysaccharides from Sargassum, strains PT2-4T and 62-3T are suggested to be classified into two novel species, Tamlana laminarinivorans sp. nov. and Tamlana sargassicola sp. nov. (type strain PT2-4T=MCCC 1K04427T=KCTC 92183T and type strain 62-3T=MCCC 1K04421T=KCTC 92182T).
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