Genetics and Physiology of Acetate Metabolism by the Pta-Ack Pathway of Streptococcus mutans

Abstract

ABSTRACTIn the dental caries pathogenStreptococcus mutans, phosphotransacetylase (Pta) catalyzes the conversion of acetyl coenzyme A (acetyl-CoA) to acetyl phosphate (AcP), which can be converted to acetate by acetate kinase (Ack), with the concomitant generation of ATP. A ΔackAmutant displayed enhanced accumulation of AcP under aerobic conditions, whereas little or no AcP was observed in the Δptaor ΔptaΔackAmutant. The Δptaand ΔptaΔackAmutants also had diminished ATP pools compared to the size of the ATP pool for the parental or ΔackAstrain. Surprisingly, when exposed to oxidative stress, the ΔptaΔackAstrain appeared to regain the capacity to produce AcP, with a concurrent increase in the size of the ATP pool compared to that for the parental strain. The ΔackAand ΔptaΔackAmutants exhibited enhanced (p)ppGpp accumulation, whereas the strain lacking Pta produced less (p)ppGpp than the wild-type strain. The ΔackAand ΔptaΔackAmutants displayed global changes in gene expression, as assessed by microarrays. All strains lacking Pta, which had defects in AcP production under aerobic conditions, were impaired in their abilities to form biofilms when glucose was the growth carbohydrate. Collectively, these data demonstrate the complex regulation of the Pta-Ack pathway and critical roles for these enzymes in processes that appear to be essential for the persistence and pathogenesis ofS. mutans.