Genome Sequence of a Novel Marine Strain Alg07 Gives Insight into the Degradation Pathways of Algal Polysaccharides and Monosaccharide

Algae are widely distributed in marine environments. Due to their special ingredients, algae can be applied in various fields, such as functional food, energy source, fertilizer, and so on. The brown alga is a large group of mostly marine algae, and a number of them are edible and good for health. The brown algae contain special polysaccharides, such as alginate, laminarin and fucoidan. The degradation products of these polysaccharides possess specific biological activities, which makes them a hot research topic. Moreover, the algal polysaccharides have been used as an energy source to produce ethanol.

The effective degradation of algal polysaccharides is very important to produce not only functional oligosaccharides but also ethanol and other energy substances. Recently, we isolated a strain Alg07 from marine area near the city of Weihai, China. It was shown that the strain was able to degrade kelp effectively and exhibited extraordinary activity to degrade alginate. According to the phylogenetic analysis based on 16S rRNA gene sequences, Alg07 was identified as the genus Bacillus, but exhibits lower similarities (< 95%) with several other well-studied Bacillus species.  Furthermore, the genome of Alg07 was sequenced and annotated. We identified the enzymes associated with the degradation of polysaccharides in the genome of Alg07 by comparison with the carbohydrate-active enzymes database (CAZymes). The genes and gene cluster for degradation of alginate were predicted and the key enzymes were successfully heterologously expressed and characterized. Interestingly, two alginate lyases exist lonely in the genome, but not be included in the gene cluster. The signal peptides were found in the N terminal of both alginate lyases, which indicated that the alginate was degraded into oligoalginate in the extracellular. The genes responsible for transporting oligoalginate to intracellular, degrading oligoalginate into unsaturated monosaccharide, and reducing monosaccharide to 2-keto-3-deoxy-d-gluconate (KDG) were arranged in a gene cluster. The gene clusters for degradation of laminarin and mannitol were disclosed. Therefore, the degradation pathways of algal polysaccharides and monosaccharide were determined in the novel marine Alg07 strain.