Cloning and characterization of a new pH-stable alginate lyase with high salt tolerance from marine Vibrio sp. NJ-04

Marine polysaccharide-degrading enzymes play an important role in marine algae degradation and carbon cycling, especially the alginate lyases. Although many alginate lyases have been characterized, the enzymes with industrial potential are still rather rare. A gene, encoding a new alginate lyase AlgNJ04, has been cloned from the marine bacterium Vibrio sp. NJ04. The recombinant alginate lyase was characterized followed by purification on Ni-NTA Sepharose. It exhibited an optimum activity (2416 U/mg) at pH 7.0 and 40 °C. Notably, the AlgNJ04 retained more than 80% of its maximum activity at a broad pH range of pH 4.0 and 10.0, which exhibited excellent pH stability. Additionally, it possessed broader substrate specificity, showing activities towards both poly β-D-mannuronate (polyM) and poly α-L-guluronate (polyG). Furthermore, the K_m values of AlgNJ04 towards sodium alginate (0.49 mM) and polyG (0.24 mM) were lower than that towards polyM (0.86 mM). Notably, the activity of AlgNJ-04 could be activated by NaCl with certain concentrations, which was partly caused by the removal of bound water from sodium alginate molecules or by the effects of charges in forming the alginate-enzyme complex. The ESI-MS analysis suggested that it mainly released oligosaccharides with DP of 2–5 as end products in an endolytic manner. Therefore, it may be a potent tool to produce alginate oligosaccharides with lower DPs.