Expression and characterization of TbCel12A, a thermophilic endoglucanase with potential in biomass hydrolysis

To increase economic benefit and reduce pollutants, agricultural biomass can be hydrolyzed to monosaccharides, which serve as a feedstock for biorefinery production of fuels and fine chemicals. In a search for new enzymes to apply to this process, Thermobispora bispora TbCel12A endoglucanase was identified by rice straw compost metagenome analysis and expressed in recombinant Escherichia coli. TbCel12A hydrolyzed both soluble and insoluble β-glucan substrates. Its highest hydrolysis rate was observed for cellopentaose compared to other cellooligosaccharides, barley mixed linkage β-glucan, and carboxymethyl cellulose. Low hydrolysis rates were observed for α-cellulose, and avicel. The primary product detected was cellobiose and a smaller amount of glucose. TbCel12A exhibited highest activity at 65 °C and pH 5.0 and retained 86% relative activity after incubation at 60 °C overnight. TbCel12A conserved >80% activity in 10% alcohol and at high salt concentrations. Hydrolysis of pretreated rice straw using commercial cellulase and TbCel12A released slightly more reducing sugars than hydrolysis using only commercial cellulase. Therefore, TbCel12A is a promising enzyme for further development for use in biomass conversion.