Removal of inhibitors of bacterial growth by dialysis culture.

Dialysis culture was used to investigate the extent to which growth inhibition in bacterial cultures may be caused by accumulation of metabolites. Escherichia coli B was grown in a glucose/salts medium. A concentrated nutrient solution was pumped at a constant rate into the growing culture to ensure that growth was not limited by exhaustion of nutrients. In this way the only difference between growth conditions in dialysis and non-dialysis cultures was the transfer of dialysable metabolites from the culture vessel to the reservoir in the dialysis culture system. By adjusting the glucose concentration in the feed and maintaining a constant rate of feeding, glucose-limited growth could be achieved. Under these conditions, with oxygen in excess, bacterial yields of 140 to 150 g dry wt l-1 were obtained in dialysis culture compared with 30 to 40 g l-1 in non-dialysis culture. The high yields in dialysis culture depended on the removal of end-products of glucose metabolism. Growth inhibition was demonstrated to be the result of the combined influence of acetate, lactate, pyruvate, succinate, propionate and isobutyrate in concentrations found at the end of growth in non-dialysis cultures of Escherichia coli B.