Involvement of Streptococcus gordonii Beta-Glucoside Metabolism Systems in Adhesion, Biofilm Formation, and In Vivo Gene Expression

Abstract

Streptococcus gordonii genes involved in beta-glucoside metabolism are induced in vivo on infected heart valves during experimental endocarditis and in vitro during biofilm formation on saliva-coated hydroxyapatite (sHA). To determine the roles of beta-glucoside metabolism systems in biofilm formation, the loci of these induced genes were analyzed. To confirm the function of genes in each locus, strains were constructed with gene inactivation, deletion, and/or reporter gene fusions. Four novel systems responsible for beta-glucoside metabolism were identified, including three phosphoenolpyruvate-dependent phosphotransferase systems (PTS) and a binding protein-dependent sugar uptake system for metabolizing multiple sugars, including beta-glucosides. Utilization of arbutin and esculin, aryl-beta-glucosides, was defective in some mutants. Esculin and oligochitosaccharides induced genes in one of the three beta-glucoside metabolism PTS and in four other genetic loci. Mutation of genes in any of the four systems affected in vitro adhesion to sHA, biofilm formation on plastic surfaces, and/or growth rate in liquid medium. Therefore, genes associated with beta-glucoside metabolism may regulate S. gordonii in vitro adhesion, biofilm formation, growth, and in vivo colonization.Streptococcus gordonii is a pioneer colonizer on the surface of human teeth, initiating the formation of dental plaque (25).Although not directly associated with dental or gingival diseases in the oral cavity, S. gordonii colonizes damaged heart valves once it enters the bloodstream in the experimental rabbit (15) and is considered to cause endocarditis in humans (1,8,12). Thus, the virulence of S. gordonii is reflected in its ability to adhere, colonize, and survive in the heart, where it is a pathogen, and on teeth in the oral cavity, where it is not. Its virulence in a specific environment may reflect expression of genes uniquely in that environment.Using an in vivo expression technology (IVET) library constructed in S. gordonii V288, at least 13 genes were shown to be expressed in vivo on infected heart valves during experimental endocarditis, but they were unexpressed in vitro under laboratory conditions (15). Since expression occurred only on heart valves, these genes were suggested to contribute to virulence and perhaps pathogenicity. Similarly, S. gordonii genes expressed during in vitro colonization of saliva-coated hydroxyapatite (sHA) were identified using the IVET library (17). Among the genes expressed during colonization of sHA and damaged heart valves in the rabbit were beta-glucoside metabolism-encoding genes. We therefore initiated in vitro studies to understand how the beta-glucoside metabolism genes might contribute to colonization of heart valves in infective endocarditis and on sHA.Bacteria ferment beta-glucoside sugar substrates, including cellobiose, arbutin, salicin, and esculin. While common in plants and useful in establishing phenotypic fermentation patterns of bacteria, the aryl-beta-disaccharides are not found in mammali...

The Two-Component Regulatory System TCS08 Is Involved in Cellobiose Metabolism ofStreptococcus pneumoniaeR6

“…two-component regulatory system (15). A previous study has shown that catabolite control protein A (CcpA) functions in carbon catabolite repression of lactose-inducible ␤-galactosidase activity in S. pneumoniae.…”

“…Closely related proteins, however, were represented by the deduced products of the bfp locus in the S. gordonii strain Challis NCTC 7688 (www.tigr.org) (Lin Tao, personal communication), which is involved in biofilm formation (data not shown) (15).…”

StreptococcusAdherence and Colonization

“…Thus, mutations in genes encoding components of quorumsensing systems, e.g., comCDE (354); TCSS, e.g., vicRK (543); GBPs (370); and metal ion permeases (503) can impair S. mutans biofilm formation. Optimal biofilm formation by S. gordonii and S. sanguinis also requires multiple gene products including sortase (428) and proteins involved with ␤-glucoside metabolism and carbon catabolite control (296,364), nucleotide biosynthesis (181), oxidative stress (322,363), and environmental sensing and signaling (193). The growth of nonmitis-group streptococci as biofilms is only just beginning to be studied, but the complexities of M serotypes, capsular serotypes, and the expression of pilus types and antigenically variable surface proteins will probably make interpretations of the molecular pathways involved extremely difficult.…”

Loss of Catabolic Function in Streptococcus agalactiae Strains and Its Association with Neonatal Meningitis

“…We found that high-risk strains (HR group) were significantly less able than low-risk strains (LR group) to use ␣-Dglucose-1-phosphate, D-ribose, ␤-methyl-D-glucoside, and D,L-␣-glycerol phosphate, and none of the 95 substrates were better used by the HR group than by the LR group (Table 1). The adaptation of a pathogen's metabolism to its environment can provide it with an advantage for growth, survival, and virulence (2,6,11,21). The loss of catabolic function by S. agalactiae strains observed here may be the result of genetic processes that have improved the organism's adaptation to conditions that generate neonatal meningitis.…”