Volume 19 Part 1 Article 72
Title: Increasing carbohydrate degradation in compost during commercial mushroom production of Agaricus bisporus?
Author: A.M. Vos, E. Jurak, G. Pels, K. Scholtmeijer, B. Bonnet, L.G. lugones, M. Kabel, H.A.B. Wösten
After 2-3 flushes of Agaricus bisporus mushroom production, champost still contains about 50% of the carbohydrates and 45% of the lignin originally present in compost. Increased uptake of the unused pool of polysaccharides may increase mushroom yield. Lignin is removed during the vegetative growth phase of A. bisporus (phase III) but less efficiently during mushroom formation (phase IV). Here, we overexpressed the manganese peroxidase gene mnp1 in A. bisporus by placing it under control of the actin promoter to improve the removal of lignin, thereby promoting accessibility of hemicellulose and cellulose. Transformants produced MnP activity in liquid malt extract while the wild type strain did not. MnP activity was 3-4 fold increased in wheat bran medium. During a semi-commercial production cycle, MnP activity per gram wet compost was increased significantly at the end of phase III (30%) while the activity was similar to the wild type strain at the initiation of mushroom formation in phase IV. This indicates that other factors than mRNA accumulation may be limiting in MnP1 production at this stage. After the 1st and 2nd flush, MnP activity was increased 3-4 fold. There was no difference in mushroom yield or biomass formation in compost as measured by chitin release. In addition, carbohydrates released after enzymatic treatment of milled compost and carbohydrate content was not affected. Finally, lignin was not affected differently by the mnp1 overexpressor as determined by pyrolysis. Efficient MnP activity in compost may have been impaired by cofactor limitation.