Streptococcus mutans: a new Gram-positive paradigm?

Abstract

Despite the enormous contributions of the bacterial paradigms Escherichia coli and Bacillus subtilis to basic and applied research, it is well known that no single organism can be a perfect representative of all other species. However, given that some bacteria are difficult, or virtually impossible, to cultivate in the laboratory, that some are recalcitrant to genetic and molecular manipulation, and that others can be extremely dangerous to manipulate, the use of model organisms will continue to play an important role in the development of basic research. In particular, model organisms are very useful for providing a better understanding of the biology of closely related species. Here, we discuss how the lifestyle, the availability of suitable in vitro and in vivo systems, and a thorough understanding of the genetics, biochemistry and physiology of the dental pathogen Streptococcus mutans have greatly advanced our understanding of important areas in the field of bacteriology such as interspecies biofilms, competence development and stress responses. In this article, we provide an argument that places S. mutans, an organism that evolved in close association with the human host, as a novel Gram-positive model organism.Advances in the field of bacteriology have relied strongly on studies involving the bacterial paradigms Escherichia coli and Bacillus subtilis. In both cases, a long history of laboratory research, ease of cultivation and genetic manipulation encouraged and provided the rationale for the emergence of these bacteria as model organisms. E. coli is a Gramnegative, non-sporulating bacterium that can be found freeliving, in water or soil, as well as associated with plants, insects, birds and mammals. It is the most studied prokaryotic organism and comprises a very heterogeneous group containing both pathogenic and non-pathogenic strains. In addition to serving as the Gram-negative model organism, laboratory strains of E. coli are extremely versatile and are the quintessential lab workhorses. Bacillus subtilis is a Gram-positive sporulating organism commonly found in soil, plants and, transiently, on the surface of animals. Strains of B. subtilis are not associated with humans and are not pathogenic, although some closely related Bacillus species such as Bacillus anthracis and Bacillus cereus are implicated in human disease (anthrax) and in food poisoning, respectively. Because the sporulation process occurs in simple well-defined stages, B. subtilis sporulation has served as a paradigm for bacterial development and differentiation studies. Like E. coli, B. subtilis is also easy to cultivate and highly amenable to genetic manipulation. The wealth of information derived from investigations of the biochemistry, physiology, genetics and developmental processes of E. coli and B. subtilis laid the foundation for, and at the same time provided guidance for, studies with other bacterial species. In addition to E. coli and B. subtilis, there are numerous other organisms that have served, in a more limited scope, a...

Effects of Arginine on Streptococcus mutans Growth, Virulence Gene Expression, and Stress Tolerance

“…Genetic competence, the ability to internalize exogenous DNA, is considered an important attribute of S. mutans for its establishment, persistence, nutrient acquisition, and genome diversification (11,32). In S. mutans, it has been established that CSP and sigX-inducing peptide (XIP) activate competence in S. mutans (33,34).…”

Stress Physiology of Lactic Acid Bacteria

“…In addition, cariogenic streptococci, such as S. mutans, need to cope with sustained acidification of their environment as a result of the production of lactic acid from fermentable sugars by LAB residing in plaque. Because of the direct linkage between low-pH survival and dental caries and the ease of genetic manipulation, S. mutans has become the bacterial paradigm for LAB acid stress responses (538). Notwithstanding this, the number of investigations that directly associate S. mutans acid stress survival pathways with caries formation is still rather limited.…”

Loss of NADH Oxidase Activity in Streptococcus mutans Leads to Rex-Mediated Overcompensation in NAD + Regeneration by Lactate Dehydrogenase

“…Dental plaque is somewhat porous, allowing the movement of fluids and nutrients, the establishment of chemical gradients, and the development of several environmental and ecological niches (4)(5)(6). S. mutans has complex stress response pathways that allow it to survive this rapidly changing environment and to thrive in dental plaque in the face of both acid and oxidative stresses (2,7).…”