Metabolism of Acetivibrio cellulolyticus during optimized growth on glucose, cellobiose and cellulose

Abstract

The growth of Acetivibrio cellulolyticus in 2.5 l batch cultures was optimized by controlling the growth pH at 6.7, the dissolved inorganic sulphide concentration at 0.4–0.6 mM, and by constant removal of hydrogen from the cultures by sparging with N2/CO2 or N2 gas. An initial ethanol concentration of 0.15% (w/v) in cellobiose media resulted in specific growth rates which were reduced by about 75% compared to growth rates of 0.17 h−1 in control cultures. Acetivibrio cellulolyticus had to be adapted for growth on glucose and 14C-radiotracer studies indicated that glucose was metabolized by the Embden-Meyerhof pathway. The specific growth rate (μ=0.03h−1) and molar growth yield (Yglucose=21.5) were considerably lower than those obtained (μ=0.17 h−1, Ycellobiose=68.9) in cellobiose media. A YATP of 12.8 was obtained during growth on cellobiose. The mol product formed per mol Avicel cellulose fermented (on anhydroglucose equivalent basis) were 3.70 H2, 2.64 CO2, 0.73 acetate, 0.39 ethanol and 0.03 total soluble sugars on glucose basis. Maximum cellulase activity was observed in cellulose-grown cultures.