Acquisition of manganous ions by mutans group streptococci

Abstract

The cariogenic bacteria Streptococcus sobrinus and S. cricetus were shown to have an absolute requirement for manganous ion in order to bind glucans or to adhere to glass in the presence of sucrose. The bacteria possessed a reasonably high affinity transport system for 54Mn2 , yielding a Km of about 12 ,M. The Vmax for uptake of 54Mn2+ in S. sobrinus was increased when the bacteria were grown in Mn-depleted medium, but the Km remained the same. There was no evidence for two Mn2+ uptake systems, commonly observed for many bacteria. Ions such as Ca2+, Co2+, Co3+, Cu2+, Fe2+, Fe3+, Hg2+, Mg2+, Ni2+, and Zn2+ did not inhibit the uptake of 54Mn2+ by the bacteria, although Cd21 was a potent inhibitor. Fractionation experiments showed that manganese was distributed in protoplasts (67%) and in the cell wall (33%). Approximately 80%o of the 54Mn2+ in S. sobrinus was rapidly exchangeable with nonradioactive Mn2+. Electron spin resonance experiments showed that all of the manganese was bound or restricted in mobility. Proton motive forcedissipating agents increased the acquisition of 54Mn2+ by the streptococci, probably because the wall became more negatively charged when the cell could no longer produce protons.Bacteria use trace metals as prosthetic groups for numerous enzymes. For many bacteria, manganous ion is essential for growth and division. Requirements for manganese occur in both gram-positive and gram-negative bacteria. Archibald (4) has reviewed the role of manganese in microbial metabolism. Drake et al. (16) found that expression of the glucanbinding lectin (GBL) of the mutans group streptococci depends on the presence of manganous ion in the growth medium. More recent work by showed that growth supplements of citrate or lactate prevented expression of GBL. The effects of citrate and lactate were probably due to the binding of manganese by the organic acids, effectively starving the cells for the metal ion. The GBL of the mutans group streptococci may function to promote their sucrose-dependent adhesion to and accumulation on the surfaces of teeth (10,11,21,22,26,27), an initial step in dental caries formation.Several lines of evidence point to a role of manganese in dental caries (6,7,9,12), although that role has yet to be defined. Adhesion to surfaces seems to favor the growth and survival of bacteria. If manganous ion contributes to the ability of streptococci to adhere, it would be expected that the bacteria possess efficient means of acquisition of the ion. In this study, it is shown that Streptococcus sobrinus and S. cricetus, both members of the mutans group of streptococci, possess a highly specific uptake system for manganous ion. Trypticase soy broth (TSB; BBL Microbiology Systems, Cockeysville, Md.). In order to eliminate potential sucrose or a-1,6-glucan contaminants, the medium was treated with yeast invertase (1 mg/g of dry medium; Sigma Chemical Co., St. Louis, Mo.) and fungal dextranase (1 mg/g of dry medium; Sigma) at 50°C for 3 h prior to autoclaving. Treatment of the medium with the enzyme...

Genome-Wide Characterization of the SloR Metalloregulome in Streptococcus mutans

“…Consistent with this finding is the reported association of manganese in tooth enamel with increased caries frequency (7). More-recent reports propose a role for divalent metal ions in S. mutans sucrose-dependent adherence that is mediated by glucosyltransferases (14). In addition, manganese functions as a necessary cofactor for streptococcal enzymes during lactic acid fermentation (14) and for superoxide dismutase (SOD), which serves as a catalyst for the conversion of toxic superoxide radicals into less harmful by-products.…”

“…More-recent reports propose a role for divalent metal ions in S. mutans sucrose-dependent adherence that is mediated by glucosyltransferases (14). In addition, manganese functions as a necessary cofactor for streptococcal enzymes during lactic acid fermentation (14) and for superoxide dismutase (SOD), which serves as a catalyst for the conversion of toxic superoxide radicals into less harmful by-products. High concentrations of free Mn 2ϩ can also provide direct protection against radical oxygen species (ROS) (24) and so further promote aerotolerance in the oral streptococci (2,4,30).…”

Inorganic Cation Transport and Energy Transduction in Enterococcus hirae and Other Streptococci

“…This gene encodes a 42-kDa hydrophobic polypeptide having 12 putative membrane-spanning regions, like most other secondary porters (263). Everted vesicles of strain WD4, in which the napA gene is disrupted, did not show uptake of 22 Na ϩ in response to a proton potential. When the napA gene was expressed in E. coli, NapA-dependent, Na ϩ -coupled H ϩ flux was observed (240).…”

“…Since the energy donor common to the metabolism of glucose and arginine is ATP, Na ϩ extrusion was attributed to an ATP-driven Na ϩ pump (89). ATP-driven 22 Na ϩ uptake and Na ϩ -stimulated ATP hydrolysis were observed in everted membrane vesicles in the presence of DCCD and the ionophores (90). No Na ϩ -pumping activity was detected in vesicles of mutant 7683 (83); this mutant is now considered to be a double mutant defective in both Na ϩ -ATPase and the Na ϩ /H ϩ antiporter (114,232).…”

The SloR/Dlg Metalloregulator ModulatesStreptococcus mutansVirulence Gene Expression

“…In fact, high concentrations of manganese have been strongly correlated with increased prevalence of dental caries (1,5). This is not surprising given that sucrose-dependent adherence and glucan binding by the mutans group streptococci both require manganese (4,25). Unlike iron, however, manganese does not promote Fenton chemistry but rather plays a crucial role in bacterial defense against oxidative stress (2,49).…”