Efficient utilization of brown algae for the production of Polyhydroxybutyrate (PHB) by using an enzyme complex immobilized on Ralstonia eutropha

Marine macroalgae are potential renewable feedstocks for valuable biomaterials. Among them, alginate is a primary component in brown algae that can be nonenzymatically converted and enzymatically degraded by alginate lyases to 4-deoxy-L-erythro-5-hexoseulose uronic acid (DEH). Here, we constructed alginolytic enzyme complexes comprising two different alginate lyases for synergistic alginate degradation. The complexes showed good thermostability with 60% of the residual activity at high temperature (60 °C). Furthermore, they produced 0.85 and 0.18 mg/mL DEH from alginate and natural brown algae as substrates, respectively. The enzyme complex successfully decomposed brown algal biomass, resulting in a 3.15-fold improvement in DEH when compared to free enzymes. The Ralstonia eutropha strain with alginolytic enzyme complexes on the cell surface showed higher Polyhydroxybutyrate (PHB) production and produced 2.58 g/L PHB from alginate. After the use of alginate, remaining biomass such as fucoidan and laminaran can also be used in the future for high value ingredients in nutritional, medical device, skincare and dermatological products. These results demonstrate that it is possible to create more efficient strategies for producing biodegradable PHB and functional polysaccharides from brown algal substrates.