Genetics of Acid Adaptation in Oral Streptococci

Abstract

A growing body of information has provided insights into the mechanisms by which the oral streptococci maintain their niches in the human mouth. In at least one case, Streptococcus mutans, the organism apparently uses a panel of proteins to survive in acidic conditions while it promotes the formation of dental caries. Oral streptococci, which are not as inherently resistant to acidification, use protective schemes to ameliorate acidic plaque pH values. Existing information clearly shows that while the streptococci are highly related, very different strategies have evolved for them to take advantage of their particular location in the oral cavity. The picture that emerges is that the acid-adaptive regulatory mechanisms of the oral streptococci differ markedly from those used by Gram-negative bacteria. What future research must determine is the extent and complexity of the acid-adaptive systems in these organisms and how they permit the organisms to maintain themselves in the face of a low-pH environment and the microbial competition present in their respective niches.

Global transcriptional analysis of acid-inducible genes in Streptococcus mutans: multiple two-component systems involved in acid adaptation

“…During intake of sweetened foodstuff, for example, carbohydrate concentrations in the oral cavity can rapidly increase from around 10 mm to well over 10 mM (Lemos et al, 2005;Lemos & Burne, 2008). Concurrent with the influx of dietary carbohydrates is a dramatic decrease in pH to values of 4 or lower in dental biofilms (Quivey et al, 2001). This socalled 'feast-and-famine' lifestyle provides some organisms, such as Streptococcus mutans, with a significant advantage in competition with other species in dental biofilms, resulting in an emergence of numerically significant members in dental plaque that may cause caries (Marsh, 1994).…”

“…This socalled 'feast-and-famine' lifestyle provides some organisms, such as Streptococcus mutans, with a significant advantage in competition with other species in dental biofilms, resulting in an emergence of numerically significant members in dental plaque that may cause caries (Marsh, 1994). These environmental variations are known to have profound impacts on bacterial gene expression and have been unequivocally shown to be the factors that influence the microbial composition and biological activities of dental plaque biofilms (Lemos et al, 2005;Marsh, 1994;Quivey et al, 2001). To persist in dental biofilms, oral bacteria must be able to sense, respond and adapt to such rapid and unexpected environmental changes.…”

“…S. mutans is therefore considered as a primary aetiological agent of dental caries (Ajdic et al, 2002). The ability of S. mutans to produce and tolerate acids is crucial to its virulence and cariogenicity (Quivey et al, 2001;Li et al, 2008). Acid tolerance by S. mutans has been studied in some detail.…”

“…Acid tolerance by S. mutans has been studied in some detail. It is well known that this organism can grow and carry out glycolysis at pH values below 5.0 and can drive the pH to values well below 4.0 (Quivey et al, 2001). The aciduricity of this organism has been attributed largely to the proton-extruding F 1 F 0 -ATPase that functions well at pH 5.0 and below, allowing the organism to maintain adequate DpH when the external pH falls to 4.0 and lower (Bender et al, 1986;Cotter & Hill, 2003).…”

Streptococcus mutans: a new Gram-positive paradigm?

“…While a normal inhabitant of the oral cavity, S. mutans is mostly known for its importance in the aetiology of dental caries and occasional association with subacute infective endocarditis. Decades of research have conclusively demonstrated that S. mutans is a major cariogenic organism by virtue of its contribution to the formation of the dental biofilm matrix, its capacity to produce large quantities of organic acids, and its ability to outcompete non-cariogenic commensal species at low pH conditions (Banas & Vickerman, 2003;Bowen & Koo, 2011;Gross et al, 2012;Lemos et al, 2005;Quivey et al, 2001).…”