Simultaneous saccharification/fermentation with zymomonas mobilis

In recent years, an ethanol production process has been developed which utilizes Trichoderma reesei cellulase and Candida brassicae I F 0 1664 in the simultaneous saccharification/fermentation (SSF) of cellulose to ethanol.The direct production of ethanol from cellulose in an SSF process alleviates the problem of end production inhibition.I Glucose does not accumulate in this system, but rather is fermented to ethanol immediately following saccharification.The result is an increase in yield of 25% or greater as compared with separate processes of saccharification and fermentation.An alternative organism which might be used in place of yeasts in ethanol production processes is Zymomonas mobifis.Rogers et al.' have described several advantages of Zymomonas, primary of which are significantly higher specific rates of glucose uptake and ethanol production.Several researchers have studied the utilization of Z. mobifis in processes similar to SSF.Viikari et al.3 tested Zymomonas strains in combined hydrolysis and ethanol production utilizing Trichoderma reesei cellulases.They found several Zymomonas strains capable of producing more ethanol than did the reference yeast Saccharomyces cerevisiae.Saddler et d.4.5 tested the ethanol production efficiency of Z. mobiiis (ATCC 29191) in an SSF type system using Trichoderma cellulase filtrates.They obtained values as high as 2% (w/v) ethanol from 5% steam exploded wood fractions.The optimum temperature for hydrolysis of cellulose by Trichoderma reesei cellulases is 50°C.4Since this hydrolysis is the rate limiting step in the SSF process,' it is advantageous to utilize the most temperature tolerant ethanol producer available.Candida brassicae is currently the organism of choice due to its ability to produce ethanol efficiently at 40°C.This investigation reports on the screening of Zymomonas strains and evaluating the feasibility of utilizing the most temperature tolerant strain in place of C .brassicae in SSF.