Expression of an auxiliary activity 9 from Chaetomium globosum in a bacterial host and its synergism in cellulose hydrolysis

Auxiliary activity family 9 (AA9), which is formerly known as glycoside hydrolase family 61 or polysaccharide monooxygenase, is a class of proteins originating from cellulolytic fungi. During the fungal growth on cellulose-containing medium, AA9s were coexpressed with hydrolytic cellulases and recently reported to show a synergistic activity with cellulase in cellulose hydrolysis via the oxidative cleavage of glycosidic linkages within cellulose polymers. Here, the functional expression of a recombinant fungal AA9 from Chaetomium globosum (CgAA9) in a bacterial host (Escherichia coli) is reported for the first time and the CgAA9 expressed in E. coli also showed a synergistic activity in cellulose hydrolysis like other AA9s expressed in eukaryotic hosts. From optimization study, significant synergism (1.7 fold) in Avicel hydrolysis was obtained when CgAA9 (0.9 mg/g cellulose) was treated together with  0.9 filter paper units of Celluclast 1.5 L/g cellulose. This is the first report of the active expression of AA9 in a bacterial host and the optimization for its synergistic acitivity in cellulose hydrolysis, which will be helpful in the industrial application of lignocellulose.