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Journal of Bacteriology, May 2008, p. 3572-3579, Vol. 190, No. 10
0021-9193/08/$08.00+0     doi:10.1128/JB.01882-07
Copyright © 2008, American Society for Microbiology. All Rights Reserved.

Concerted Action of Lactate Oxidase and Pyruvate Oxidase in Aerobic Growth of Streptococcus pneumoniae: Role of Lactate as an Energy Source

Departments of Bacteriology,¹ Environmental Medicine and Infectious Diseases,² Pediatrics, Faculty of Medical Sciences,³ Department of Oral Health, Growth, and Development, Division of Oral Infectious Diseases and Immunology, Faculty of Dental Science, Kyushu University, Higashi-ku, Fukuoka 812-8582, Japan⁴

Received 30 November 2007/ Accepted 4 March 2008

Streptococcus pneumoniae was shown to possess lactate oxidase in addition to well-documented pyruvate oxidase. The activities of both H₂O₂-forming oxidases in wild-type cultures were detectable even in the early exponential phase of growth and attained the highest levels in the early stationary phase. For each of these oxidases, a defective mutant was constructed and compared to the parent regarding the dynamics of pyruvate and lactate in aerobic cultures. The results obtained indicated that the energy-yielding metabolism in the wild type could be best described by the following scheme. (i) As long as glucose is available, approximately one-fourth of the pyruvate formed is converted to acetate by the sequential action of pyruvate oxidase and acetate kinase with acquisition of additional ATP; (ii) the rest of the pyruvate is reduced by lactate dehydrogenase to form lactate, with partial achievement of redox balance; (iii) the lactate is oxidized by lactate oxidase back to pyruvate, which is converted to acetate as described above; and (iv) the sequential reactions mentioned above continue to occur as long as lactate is present. As predicted by this model, exogenously added lactate was shown to increase the final growth yield in the presence of both oxidases.

Published ahead of print on 14 March 2008.