Catabolic pathway for aerobic degradation of lactate by Actinomyces naeslundii

Abstract

The aerobic metabolism of lactate by oral Actinomyces was studied. Six of 7 strains of Actinomyces naeslundii increased their growth in the presence of lactate under aerobic conditions. Washed cells grown on lactate aerobically degraded lactate and pyruvate to acetate with a concomitant consumption of oxygen. In the presence of catalase, the molar ratios of oxygen consumed to acetate produced were 1 for lactate degradation and 0.5 for pyruvate degradation. The enzymatic activities found in cell extracts revealed that lactate could be converted to pyruvate by NAD-independent lactate dehydrogenase (iLDH) and further to acetyl CoA by pyruvate dehydrogenase (PDH). The acetyl CoA formed could be metabolized into acetate by phosphotransacetylase (PTA) and acetate kinase (AK) with the formation of ATP. These results indicate that A. naeslundii metabolizes lactate into acetate by the sequential enzymatic reactions iLDH, PDH, PTA and AK and that hydrogens produced by iLDH and PDH are transferred to oxygen. The activity of lactate degradation and oxygen consumption may modify the environmental conditions of dental plaque.

Glucose and Lactate Metabolism By Actinomyces Naeslundii

“…3). The pyruvate dehydrogenase activity is thiamine pyrophosphate-, NAD-, and CoA-dependent (Takahashi and Yamada, 1996) and is similar to the other bacterial pyruvate dehydrogenases (Read and Willms, 1966;Carlsson et al, 1985). The acetyl CoA formed is converted into acetate through the same pathway as that functioning under anaerobic conditions.…”

“…During aerobic glucose fermentation, A. naeslundii cells consume a large amount of oxygen (van der Hoeven and van den Kieboom, 1990;Takahashi and Yamada, 1996). The reducing potential (NADH) derived from glyceraldehyde-phosphate dehydrogenase and pyruvate dehydrogenase is transferred to oxygen by NADH oxidases (reaction 22, Fig.…”

Actinomyces naeslundii in initial dental biofilm formation

“…A pH-modulating activity of these species may, theoretically, occur also via degradation of urea (Yaling et al, 2006). Moreover, through its metabolism, Actinomyces species can remove oxygen from the environment and create an anaerobic milieu (Takahashi & Yamada, 1996), suitable for outgrowth of some other bacteria. Finally, recent observations demonstrate that co-aggregation with A. naeslundii stabilizes arginine metabolism in Streptococcus gordonii and reduces its dependence on extracellular arginine, which is a limiting factor in the environment of the early colonizers (Jakubovics et al, 2008;Van Wuyckhuyse et al, 1995).…”

“…Actinomyces species can use lactate as a carbon source for growth (Takahashi & Yamada, 1996;van der Hoeven & van den Kieboom, 1990), whereby lactic acid is converted into weaker acids (Takahashi & Yamada, 1996). A pH-modulating activity of these species may, theoretically, occur also via degradation of urea (Yaling et al, 2006).…”

“…Several culturebased studies indicated that Actinomyces species gain increased prominence at the expense of streptococci during maturation of the biofilm (Ritz, 1967; Socransky et al, 1977;Syed & Loesche, 1978;van Palenstein Helderman, 1981). Such population changes might reflect differences in growth rates (Nyvad & Kilian, 1987; Socransky et al, 1977) and/or differences in nutritional profiles of these genera (Takahashi et al, 1995;Takahashi & Yamada, 1996;van der Hoeven & van den Kieboom, 1990;Yaling et al, 2006). However, the spatial relationship of actinomycetes with other members of the dental biofilm microbiota was not disclosed by these culture-based studies.…”