Novel Endoglucanases of the Thermophilic Cellulolytic Bacterium Melioribacter roseus

Two genes from the moderately themophilic chemoorganotrophic bacterium Melioribacter roseus, predicted to encode endoglucanases, were cloned and expressed in Escherichia coli. Gene Mros0753 encodes GH5 family hydrolase, whereas Mros0757 represents the GH9 family. Recombinant endoglucanase Mros0757 exhibited high specific activity of 7353 U/mg on carboxymethyl cellulose at 65°C. Endoglucanase Mros0753 has seven times lower specific activity but higher temperature optima at 80°C. Both enzymes were not able to hydrolyse microcrystalline cellulose and showed no beta-glucosidase, beta-galactosidase, beta-mannosidase and beta-xylosidase activities. Weak activity against xylan was observed only for Mros0753. Analysis of cellulose hydrolysis products revealed that both enzymes generate mostly cellobiose, and minor amounts of glucose and cello-oligosaccharides longer than cellopentaose. Cellobiose was not digested. The presence of two endoglucanases could ensure efficient hydrolysis of soluble cellulose by M. roseus at different temperatures. The new endoglucanases could be useful for saccharification of lignocellulosic biomass.