Glucose Fermentation by Propionibacterium microaerophilum: Effect of pH on Metabolism and Bioenergetics

pH affected significantly the growth and the glucose fermentation pattern of Propionibacterium microaerophilum. In neutral conditions (pH 6.5-7.5), growth and glucose fermentation rate (qs) were optimum producing propionate, acetate, CO sub(2), and formate [which together represented 90% (wt/wt) of the end products], and lactate representing only 10% (wt/wt) of the end products. In acidic conditions, propionate, acetate, and CO sub(2) represented nearly 100% (wt/wt) of the fermentation end products, whereas in alkaline conditions, a shift of glucose catabolism toward formate and lactate was observed; lactate representing 50% (wt/wt) of the fermentation end products. The energy cellular yields (Y sub(X/ATP)), calculated (i) by taking into account extra ATP synthesized through the reduction of fumarate into succinate, was 6.1-7.2 g/mol. When this extra ATP was omitted, it was 11.9-13.1 g/mol. The comparison of these values with those of Y sub(X/ATP) in P. acidipropionici and other anaerobic bacteria suggested that P. microaerophilum could not synthesize ATP through the reduction of fumarate into succinate and therefore differed metabolically from P. acidipropionici.