The alginate lyases FlAlyA, FlAlyB, FlAlyC, and FlAlex from Flavobacterium sp. UMI-01 have distinct roles in the complete degradation of alginate

We recently reported the isolation of Flavobacterium sp. UMI-01 as a novel alginate-assimilating bacterium from decayed brown algae. In our previous study, FlAlyA was purified and characterized as an endolytic alginate lyase, producing alginate oligosaccharides (AOSs) from its polymer. Additionally, crude extracts from strain UMI-01 were found to be capable of producing of 4-deoxy-l-erythro-5-hexoseulose uronic acids (DEHs) through degradation of AOSs. Here, we report the enzymatic characteristics of four alginate lyases, i.e., FlAlyA, FlAlyB, FlAlyC, and FlAlex, found in the genomic sequence of UMI-01 using recombinant proteins. Our results demonstrated that the distinct roles of these enzymes facilitated complete degradation of alginate to DEH in strain UMI-01. First, FlAlyA attacked the alginate polymer in an endolytic manner, producing AOS. Recombinant FlAlyA could completely degraded alginate into AOS in vitro, and its activity was 20-52-fold higher than those of commercially available enzymes. Next, DEH was generated as a final degradation product through the functions of FlAlyB, FlAlyC, and FlAlex, which exhibited distinct substrate preferences; FlAlyB, FlAlyC, and FlAlex were identified as polyM-, polyMG-, and polyG-specific enzymes, respectively. Thus, our results confirmed that the combination of these four enzymes resulted in the most efficient degradation of alginate to DEH in vitro.