Effect of manganese on preferential degradation of lignin by Pleurotus ostreatus during solid-state fermentation

Practical utilization of the polysaccharides in the lignocellulosic complex is limited because of the high lignin content of the complex. In this study we focused on the effect of Mn on lignin and cellulose biodegradation during solid-state fermentation by the edible mushroom Pleurotus ostreatus. Preferential degradation of lignin was enhanced by the addition of Mn(II) to cotton stalks at concentrations ranging from 30 to 620 micrograms of Mn per g. This effect was most apparent when we compared mineralization rates of [14C] lignin with mineralization rates of [14C] cellulose. Enhanced selectivity was also observed when we analyzed residual organic matter at the end of the fermentation period by using crude fiber analysis. The cellulose fraction in the original material was 1.8 times larger than the cellulose fraction of lignin. The cellulose/lignin ratio increased during 32 days of solid-state fermentation from 2.5 in the control to 3.3 following the addition of Mn to the medium. The in vitro digestibility value for fermented cotton stalks was 53% of the dry matter. Addition of 600 micrograms of Mn per g to the cotton stalks resulted in a digestibility value of 65.4%. Enhancement of preferential lignin degradation could be result of either increased activity of the ligninolytic enzymes or production of Mn (III), which might preferentially degrade aromatic structures in the lignocellulosic complex.