Solid substrate cultivation of anaerobic thermophilic bacteria for the production of cellulolytic enzymes

Experiments were conducted to examine the feasibility of using thermophilic anaerobic bacteria in solid substrate cultivation (SSC) for enzyme production. Nine strains of bacteria were examined in submerged liquid cultivation (SmC) using corn stover, sugar cane bagasse, paper pulp sludge and wheat bran as substrates. Fifteen organism-substrate combinations produced more than 5 mM of individual ethanol, lactate and acetate end products, and were further investigated in SSC. Some combinations produced greater total end product concentrations in SSC than SmC, including C. thermocellum 27405 on paper pulp producing 289.4 +/- 39.2 mM and 83.5 +/- 5 mM, respectively.; The effects of substrate moisture content (30%, 50% and 70% wet-basis), supplemental nutrient concentration (12%, 50%, and 100%) and cultivation duration (6, 10 and 14) were investigated during the growth of C. thermocellum 27405 on paper pulp sludge. The combination of 70% substrate moisture content and 100% supplemental nutrient concentration provided the most promising SSC conditions for production. Similar results were also found during growth on Avicel. Interestingly, acetate was the primary end product for C. thermocellum 27405 in SSC, making up approximately 76% of the total end product concentration on paper pulp sludge and 61% on Avicel.; Saccharification studies were completed at 37°C and 60°C to examine the effectiveness of the SSC enzymes on complex cellulosic substrates. The reducing sugar accumulation was 4.8 +/- 3.3 mg at 37°C and 8.8 +/- 6.0 mg at 60°C on Avicel. Hydrolysis of paper pulp sludge by the SSC enzymes produced 13.2 +/- 9.7 mg of reducing sugars at 37°C, however the enzymes did not show activity at 60°C.; A New Brunswick BioFlo 3000 reactor was modified to support the growth of C. thermocellum 27405 in SSC on paper pulp sludge. The larger scale production did not inhibit the metabolic activity of the microorganism. The monitored temperature measurements indicated that the microbial heat generation was small and SSC of C. thermocellum 27405 would require continuous heat input. A mathematical model developed was able to identify yield coefficients significant to the simulation of bacterial growth and heat transfer in an ideal SSC deep bed reactor.