Abstract:

Objective: In order to explore the cooperative mechanism to degrade lignin between Monochamus alternatus and its gut bacteria, the lignin-degrading function of Serratia marcescens, a dominant bacterium living in the larval gut of M. alternatus, was studied. Method: Liquid kraft lignin medium was used to cultivate this bacterium. The degradation of lignin by S. marcescens was measured by the method of microtitration and the characteristic of lignin-degradation enzyme (LiP). Meanwhile, influences of different culture conditions on enzymatic activity of Lip, a dominant lingin-degrading enzyme which was produced by S. marcescens, had been studied. Result: It was showed that the accumulated degradation rate of the kraft lignin by S. marcescens was up to 94.12% in ten days, and the highest enzymatic activity was reached on the 4th day after inoculation. This bacterium could produced lignin peroxidase(LiP), manganese peroxidase(MnP) and laccase(Lac) in medium of lignin, and the enzymatic activity of LiP was highest, followed by MnP and Lac, and the daily variation tendency of the former two kinds of enzymes were similar with the degradation rate of lignin in the medium. The optimal medium contained 3 g·L^-1 lignin, 5 g·L^-1 yeast extract as organic nitrogen sources, 0.20 g·L^-1 Mg²⁺, 0.40 g·L^-1 Ca²⁺, 0.15 g·L^-1Fe²⁺, 0.04 g·L^-1 Mn²⁺, 0 g·L^-1 K⁺, and the optimum condition is pH value of 5.0. Conclusion: S. marcescens had strong ability to degrade lignin through producing LiP and MnP. The LiP enzymatic activity could be significantly affected by the concentration of lignin, pH, kinds and concentrations of nitrogen source, concentrations of mental irons.

Key words: Serratia marcescens, lignin-degrading enzyme, lignin peroxidase, Monochamus alternatus, larval gut