Studies On Enhancing Biological Saccharification Of Biomass By Clostridium Thermocellum Cultures With Triton X-100 And ?-glucosidase Supplementation

Nowadays,biofuels have become a significant alternative source of energy.Biofuels are liquid or gaseous fuels and they originate from biogenic material and include fuels derived from conversion of biodegradable materials called biomass.Compared to most other fuels,the main feature of biofuels is that energy produced through these sources can be renewable.This characteristic of biofuels makes them different from other energy sources commonly used today such as nuclear fuels,coal,and petroleum.Since biofuel production leads to efficient production of energy from organic material,provides recycling of organic wastes and prevents environmental pollution,economic and environmental evaluation of biofuel production has gained importance in recent years.This study investigated saccharification of Avicel and sugarcane bagasse(SCB)by Clostridium thermocellum cultures from several aspects:1)Investigation on the enhancing biological saccharification of cellulose by C.thermocellum with Triton X-100 addition;2)Optimal condition of saccharification of SCB by C.thermocellum with Triton X-100 addition;3)Enhanced saccharification of SCB by C.thermocellum cultures with Triton X-100 and ?-glucosidase addition;4)Study of synergistic between C.thermocellum cultures and CTec2 in saccharification.Biodegradation of cellulose by C.thermocellum cultures accompanied by accumulation of reducing sugars was remarkably improved with the addition of nonionic surfactant Triton X-100.The potential reasons of enhancing saccharification of cellulose by C.thermocellum cultures with Triton X-100 supplement was investigated in this study.Triton X-100 showed the detrimental effect on growth and metabolism of C.thermocellum,resulting in less transportation and consumption of reducing sugar.On the other hand,Triton X-100 had positive effect on enzyme activity and concentration in the broth,indicating that cellulases or cellulosome might be released from cell surface.When 40 g/L alkali-pretreated sugarcane bagasse(SCB)was used as substrate and under the optimal condition,namely the addition time of Triton X-100 was 48 h after inoculation,initial pH and temperature was 5.5 and 55?separately,anaerobic condition,the glucose accumulated to 10.72 g/L and the hydrolysate slurry containing glucose could be fermented to ethanol by yeast without any other nutrients added.When rapid growing culture C.thermocellum DSM 1313 was used as strain,a notable accumulation of cellobiose was detected in broth and the glucose production was significantly enhanced with 0.25%Triton X-100 and 30 CBU/g of P-glucosidase supplementation.The glucose accumulation of 21.33±0.35 g/L and substrate degradation of 61.91 ±0.77%from 60 g/L sodium hydroxide-pretreated SCB were reached,with a 609.41%and 75.53%increase over the control(3.01±0.26 g/L,35.27±2.91%),respectively.More interestingly,a synergism between C.thermocellum cultures and CTec2(30 CBU/g,1.2 FPU/g substrate)in enzymolysis of Avicel rather than SCB was observed.And the glucose concentration and saccharification ratio of Avicel reached 56.90± 1.20 g/L and 94.8%at 60 g/L Avicel.Moreover,the highest glucose concentration of 83.17 g/L was achieved at 100 g/L Avicel.The present work put forward a novel and efficient strategy to enhance glucose production by combination of C.thermocellum culture and commercial cellulase CTec2 from Avicel.No separation and purification procedures were needed and few dosage of CTec2 was used,both of which provide a promising way for saccharification of Avicel as well as lignocellulose.