Abstract

Some of Bacillus strains, especially Bacillus pumilus, were the best acetoin producers. This study attempts to disclose the mechanisms of vigorous acetoin excretion using B. pumilus ATCC 14884 as a model strain.  The production of acetoin by this strain has been studied under a variety of conditions. Glucose was found to be a much better substrate than citrate, pyruvate, succinate, or fumarate for acetoin production.  Malonate was used to slow down the Krebs cycle and the addition of 0.10 M malonate was found to inhibit cell growth slightly, but reduce the production of acetoin by 13%. The addition of 100 g/L NaCl strongly reduced cell growth and acetoin formation. On the other hand, 200 g/L glucose reduced the rate of cell growth, but led to the largest final acetoin production of all the conditions studied. Linear relationships between acetoin accumulation and cell biomass, which increased in the lag and arithmetic growth phases were found when glucose was used as the carbon source, which corroborated acetoin as a primary metabolite.  Metabolite study indicated that there were few minor pathways for by-products.  Acetoin was utilized as a preferential carbon source without the catabolite repression of glucose, suggesting that the main physiological function of acetoin excretion is an energy-storing strategy in this species.

Key words: Acetoin, biomass, association, metabolism, Bacillus pumilus.