Expression and characterization of a new heat-stable endo-type alginate lyase from deep-sea bacterium Flammeovirga sp. NJ-04

Alginate lyases play an essential role in the production of oligosaccharides by degrading alginate polysaccharide. Although many alginate lyases from various microorganisms have been characterized, reports on alginate lyases with special characteristics and commercial potential are still rather rare. In this study, a new alginate lyase, FsAlgA, was cloned from the deep-sea marine bacterium Flammeovirga sp. NJ-04. The recombinant enzyme was purified on Ni-NTA sepharose and then characterized in detail. It exhibited the highest activity (3343.7 U/mg) at pH 7.0 and 50 °C. Notably, the FsAlgA retained more than 80% of its maximum activity after incubation at 50 °C for 30 min, suggesting that FsAlgA was a heat-stable alginate lyase. Additionally, FsAlgA possessed broad substrate specificity, showing high activities toward both poly β-d-mannuronate (polyM) and poly α-l-guluronate (polyG). Furthermore, the K_m values of FsAlgA toward sodium alginate (0.48 mM) and polyG (0.94 mM) were lower than that toward polyM (1.42 mM). The TLC and ESI–MS analyses indicated that FsAlgA endolytically degraded alginate polysaccharide and released oligosaccharides with degree of polymerization (DP) of 2–5. Therefore, it may be a potent tool to produce alginate oligosaccharides with low DPs.