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

Abstract

In the dental caries pathogen Streptococcus 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 ⌬ackA mutant displayed enhanced accumulation of AcP under aerobic conditions, whereas little or no AcP was observed in the ⌬pta or ⌬pta ⌬ackA mutant. The ⌬pta and ⌬pta ⌬ackA mutants also had diminished ATP pools compared to the size of the ATP pool for the parental or ⌬ackA strain. Surprisingly, when exposed to oxidative stress, the ⌬pta ⌬ackA strain 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 ⌬ackA and ⌬pta ⌬ackA mutants exhibited enhanced (p)ppGpp accumulation, whereas the strain lacking Pta produced less (p)ppGpp than the wild-type strain. The ⌬ackA and ⌬pta ⌬ackA mutants 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 of S. mutans. Streptococcus mutans is a facultatively anaerobic, Gram-positive bacterium with fermentative metabolism. Human dental caries is associated with increased proportions of multiple acid-tolerant species in tooth biofilms, but S. mutans shows a particularly strong association with the initiation and progression of this common infectious disease (1, 2). The pathogenic potential of S. mutans is highly dependent on its ability to form biofilms, to use a variety of carbohydrates to produce organic acids that dissolve tooth mineral, and to tolerate stresses commonly encountered in oral biofilms. In particular, tolerance of a variety of reactive oxygen species (ROS), including superoxide ions and hydrogen peroxide, is considered critical for S. mutans to overcome antagonism by oral commensals and host defenses (3, 4).S. mutans has a partial tricarboxylic acid (TCA) cycle and lacks cytochromes, so the primary route for ATP generation by this organism is through the Embden-Meyerhof-Parnas pathway (4-7). Under anaerobic conditions and with growth in the presence of an excess of a preferred carbohydrate, the pyruvate generated by glycolysis is acted on by lactate dehydrogenase (LDH), which is allosterically activated by fructose-1,6-bisphosphate (F-1,6-BP), to produce lactate and regenerate NAD (4, 8). If carbohydrate is limiting, S. mutans produces a pyruvate formate lyase enzyme, which converts pyruvate to acetyl coenzyme A (acetyl-CoA) and formate (Fig. 1). However, the pyruvate formate lyase (PFL) enzyme of S. mutans is inactivated by oxygen, so under aerobic conditions and if catabolite repression is alleviated (M. Watts and R. A....

Redox Imbalance Underlies the Fitness Defect Associated with Inactivation of the Pta-AckA Pathway in Staphylococcus aureus

“…10 Interestingly, similar observations were also noted in other bacteria, i.e. it was shown that disruption of the pta gene in Escherichia coli 40 and inactivation of the ackA gene in Streptococcus mutans 41 did not cause a substantial loss in the amounts of generated ATP.…”

CcpA and CodY Coordinate Acetate Metabolism in Streptococcus mutans

“…KEYWORDS acid tolerance, carbohydrate metabolism, dental caries, gene regulation, pyruvate E stimates from evolutionary genomic analysis of over 50 isolates of the dental caries pathogen Streptococcus mutans from around the globe (1) are consistent with the bacterial composition of a small number of samples of dental calculus from ancient human fossils; both predict that S. mutans became a significant constituent of human oral biofilms around 3,000 to 10,000 years ago (2, 3), the time when humans adopted hydrate metabolism and in the ability of the organisms to cope with stressors that are commonly encountered in the oral cavity, particularly oxidative stress (30). The Pta-Ack pathway involves Ack-dependent generation of ATP and acetate from acetyl phosphate (AcP), which can be produced from acetyl coenzyme A (acetyl-CoA) and phosphate by Pta.…”

“…In particular, the ilv and leu genes encode the biosynthetic enzymes to convert pyruvate to BCAAs (7). Notably, we showed previously that ilvE (SMU.1203c) expression was downregulated in an ackA mutant, which accumulates AcP levels at much higher levels than the wild-type strain (30). To investigate the interrelationship of the Pta-Ack and BCAA biosynthetic pathways further, we monitored growth of pta and ackA mutant strains in FMC medium with modified BCAA composition (Fig.…”

Antidiabetic “gliptins” affect biofilm formation byStreptococcus mutans

“…The 12 proteins that were differentially expressed in response to both drug treatments were noted to include enolase (SMU.1247), which can be a moonlighting surface-associated protein in S. mutans (Ge et al, 2004), and acetate kinase (SMU.1978), which participates in the Pta-Ack pathway that can influence biofilm formation. (Kim et al, 2015) In conclusion, through this work we were able to establish a potential role of pepX in biofilm development of S.mutans and moved a step forward in the identification and development of novel Sm-DPP IV inhibitors. We have also tried to demonstrate the likely effect of AHD drugs on bacteria, as a proof of the concept that many regularly used drugs may exert some sort of side activity against microbes transiently or permanently inhabiting the human body.…”