Microaerophilic property of Actinobacillus actinomycetemcomitans in fructose-limited chemostat cultures

Abstract The effect of oxygen on the growth, metabolism, and leukotoxin production of Actinobacillus actinomycetemcomitans 301-b was examined using a chemostat equipped with a redox potential control system. Steady states were obtained with fructose-limited cultures grown at a dilution rate of 0.1 h⁻¹ under strictly anaerobic ( E _h=−460 mV) and microaerobic conditions ( E _h≤ 150 mV) but not under highly aerated conditions ( E _h≥ 100 mV). The optimum growth was recorded at E _h=−300 to − 200 mV and the recorded Y _fructose value was about 1.3 times the Y _fructose of anaerobic cultures. Although the organism contains a respiratory chain, the increased Y _fructose under the microaerobic conditions might result from the increased substrate-level phosphorylation at the site of acetate kinase but not from electron transport phosphorylation. After passing threshold aeration ( E _h=−100 mV), the culture yielded a variant with transparent colony morphology. Under anaerobic conditions, the Y _fructose of the variant was about 1.6 times that of the original opaque colony-forming cells. The optimum growth of the variant was also recorded at E _h=− 300 to − 200 mV. In both types of cells, the production of leukotoxin reached a maximum at E _h=−350 to − 200 mV. These findings suggested the microaerophilic nature of A. actinomycetemcomitans .