Fermentative bacteria maintain a pH gradient across the membrane and
regulate the internal pH which is essential for stability and functioning of
metabolic enzymes . Studies with C. acetobutylicum
reported that when acetate and butyrate production decrease external pH,
acids accumulate inside cells and lower their internal pH to maintain a
constant pH gradient . However,
accumulation of high concentrations of undissociated acid inside the cells
stresses them and decreases the pH gradient. Thus, the cells counteract by
producing solvents