PROTON AND CARBON INVENTORY DURING THE GROWTH OF AN ALKALIPHILIC BACILLUS INDICATES THAT PROTONS ARE INDEPENDENT FROM ACID ANIONS

Sugar catabolism and pa-dynamics in culture medium of an alkaliphilic bacterium, Bacillus circulans var. alkalophilus were studied. The moles of carbon in 1% glucose (55 mmol/l) media were recovered almost quantitatively in acetic acid (65-75 mmol/l), formic acid (40-45 mmol/l) and CO2 (90-100 mmol/l). The moles of acids needed to achieve the minimum pH of the medium during bacterial growth approximately corresponded to the moles of produced acids. However, the timing of the pH minimum did not match with the appearance of the acids, but the required amount of acids were detected several hours later in the medium. During active growth, the concentration of dissolved oxygen remained zero at all reasonable aeration levels in a fermenter. It was concluded that sugars are not metabolized through the tricarboxylic acid cycle, but the reduction potential generated from dehydrogenation of sugars is the driving force for the growth followed by the very effective transfer of hydrogen atoms/protons onto molecular oxygen/oxygen anion. The eventual rise of the pH shall result from re-equilibration of the redox state, and not from consumption of acids or generation of basic compounds as suggested previously.