EFFECTS OF DILUTION RATE AND PH ON THE RUMINAL CELLULOLYTIC BACTERIUMFIBROBACTER-SUCCINOGENES S85 IN CELLULOSE-FED CONTINUOUS-CULTURE

The ruminal cellulolytic bacterium Fibrobacter succinogenes S85 was gr own in cellulose-fed continuous culture at 22 different combinations o f dilution rate (D, 0.014-0.076 h-1) and extracellular pH (6.11-6.84). Effects of pH and D on the fermentation were determined by subjecting data on cellulose consumption, cell yield, product yield (succinate, acetate, formate), and soluble sugar concentration to response surface analysis. The extent of cellulose conversion decreased with increasin g D. First-order rate constants at rapid growth rates were estimated a s 0.07-0.11 h-1, and decreased with decreasing pH. Apparent decreases in the rate constant with increasing D was not due to inadequate mixin g or preferential utilization of the more amorphous regions of the cel lulose. Significant quantities of soluble sugars (0.04-0.18 g/l, prima rily glucose) were detected in all cultures, suggesting that glucose u ptake was rather inefficient. Cell yields (0.11-0.24 g cells/g cellulo se consumed) increased with increasing D. Pirt plots of the predicted yield data were used to determined that maintenance coefficient (0.04- 0.06 g cellulose/g cells . h) and true growth yield (0.23-0.25 g cells /g cellulose consumed) varied slightly with pH. Yields of succinate, t he major fermentation endproduct, were as high as 1.15 mol/mol anhydro glucose fermented, and were slightly affected by dilution rate but wer e not affected by pH. Comparison of the fermentation data with that of other ruminal cellulolytic bacteria indicates that F. succinogenes S8 5 is capable of rapid hydrolysis of crystalline cellulose and efficien t growth, despite a lower mu(max) on microcrystalline cellulose.