Characterization of Glaciecola sp. enzymes involved in the late steps of degradation of sulfated polysaccharide ulvan extracted from Ulva ohnoi

Net cage aquaculture alters the co-occurrence network and functions of bacterial communities in offshore areas

A better understanding of bacterial communities and the factors that drive them is essential to maintain their functions and services. As an ecosystem closely linked to human activities, the health of offshore aquaculture depends on the diversity and functions of bacteria in its environment. However, little attention has been paid to the vertical interface of the offshore aquaculture areas with shellfish net cages. In this study, high-throughput sequencing was used to analyze bacterial communities in different water layers of a net cage scallop farm in the offshore area of Northeast of China. Based on the results, an increased richness of bacterial communities was observed in the water adjacent to the net cages. Meanwhile, apparently different bacterial community compositions were observed among the water layers, with an enrichment of Cyanobacteria, Bacteroidota, and Firmicutes in the water layers above, parallel to, and below the net cages, respectively. According to the predicted functions, the bacterial communities of the water layers above, parallel to, and below the net cages were identified as phototrophy-, chemoheterotrophy-, and nitrogen respiration-dominated. Furthermore, network analysis revealed a complex but unstable bacterial community in the water layer containing the net cage. Finally, partial least squares path modelling revealed that the net cage aquaculture directly influenced the environmental variables and bacterial richness, which further induced the variations in bacterial community composition, and ultimately affected their ecological functions. These results provide a basic understanding of bacterial communities in net cage scallop farms and highlight the effects of offshore aquaculture on variations in ecological functions.

Biochemical characterisation of a PL24 ulvan lyase from seaweed-associated Vibrio sp. FNV38

Ulvan is a green macroalgal cell wall polysaccharide that has tremendous potential for valorisation due to its unique composition of sulphated rhamnose, glucuronic acid, iduronic acid and xylose. Several potential applications such as production of biofuels, bioplastics and other value-added products necessitate the breakdown of the polysaccharide to oligomers or monomers. Research on ulvan saccharifying enzymes has been continually increasing over the last decade, with the increasing focus on valorisation of seaweed biomass for a biobased economy. Lyases are the first of several enzymes that are involved in saccharifying the polysaccharide and several ulvan lyases have been structurally and biochemically characterised to enable their effective use in the valorisation processes. This study investigates the whole genome of Vibrio sp. FNV38, an ulvan metabolising organism and biochemical characteristics of a PL24 ulvan lyase that it possesses. The genome of Vibrio sp. FNV38 has a diverse CAZy profile with several genes involved in the metabolism of ulvan, cellulose, agar, and alginate. The enzyme exhibits optimal activity at pH 8.5 in 100 mM Tris-HCl buffer and 30 °C. However, its thermal stability is poor with significant loss of activity after 2 h of incubation at temperatures above 25 °C. Breakdown product analysis reveals that the enzyme depolymerised the polysaccharide predominantly to disaccharides and tetrasaccharides.

Supplementary Information

The online version contains supplementary material available at 10.1007/s10811-023-03136-3.

Prebiotic potential of enzymatically produced ulvan oligosaccharides using ulvan lyase of Bacillus subtilis, NIOA181, a macroalgae-associated bacteria

AIMS

To characterize the polysaccharide hydrolyzing potential of macroalgae-associated bacteria (MABs) for enzymatic production of oligosaccharides and determining their prebiotic potential.

METHODS AND RESULTS

Approximately 400 MABs were qualitatively characterised for polysaccharide hydrolyzing activity. Only about 5 to 15% of the isolates were found to have the potential for producing porphyranase, alginate lyase and ulvan lyase enzymes which were quantified in specific substrate broths. One potential MAB, Bacillus subtilis, NIOA181, isolated from green macroalgae, showed the highest ulvan lyase activity. This enzyme was partially purified and used to hydrolyse ulvan into ulvan oligosaccharides. Structural characterization of ulvan oligosaccharides showed that they are predominantly composed of di-, tri-, and tetrasaccharide units. Results showed that the enzymatically produced ulvan oligosaccharides exhibited prebiotic activity by promoting the growth of probiotic bacteria and suppressing the enteric pathogens, which were higher than the ulvan polysaccharide and equivalent to commercial fructooligosaccharides.

CONCLUSIONS

A potential MAB, NIOA181, producing ulvan lyase was isolated and used for the production of ulvan oligosaccharides with prebiotic activity.

SIGNIFICANCE AND IMPACT OF STUDY

Rarely studied ulvan oligosaccharides with prebiotic activity can be widely used as an active pharmaceutical ingredient in nutraceutical and other healthcare applications.

Insights into Algal Polysaccharides: A Review of Their Structure, Depolymerases, and Metabolic Pathways

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.

Marine microbial enzymes for the production of algal oligosaccharides and its bioactive potential for application as nutritional supplements

Marine macroalgae have a very high carbohydrate content due to complex algal polysaccharides (APS) like agar, alginate, and ulvan in their cell wall. Despite numerous reports on their biomedical properties, their hydrocolloid nature limits their applications. Algal oligosaccharides (AOS), which are hydrolyzed forms of complex APS, are gaining importance due to their low molecular weight, biocompatibility, bioactivities, safety, and solubility in water that makes it a lucrative alternative. The AOS produced through enzymatic hydrolysis using microbial enzymes have far-reaching applications because of its stereospecific nature. Identification and characterization of novel microorganisms producing APS hydrolyzing enzymes are the major bottlenecks for the efficient production of AOS. This review will discuss the marine microbial enzymes identified for AOS production and the bioactive potential of enzymatically produced AOS. This can improve our understanding of the biotechnological potential of microbial enzymes for the production of AOS and facilitate the sustainable utilization of algal biomass. Enzymatically produced AOS are shown to have bioactivities such as antioxidant, antiglycemic, prebiotic, immunomodulation, antiobesity or antihypercholesterolemia, anti-inflammatory, anticancer, and antimicrobial activity. The myriad of health benefits provided by the AOS is the need of the hour as there is an alarming increase in physiological disorders among a wide range of the global population.