The effect of manganese on virulence gene expression in streptococcus mutans

Streptococcus mutans was tested for its ability to grow in the absence or presence of various concentrations of manganese. The effect of manganese on the expression of virulence genes in Streptococcus mutans was also tested. Planktonic cultures of S. mutans. Serotype c strains UA159, UA130, 3200, Ingbritt, LT11, ATCC 25175 and GS-5 were grown in semi-chemically defined medium in the absence or various concentrations of manganese under three different atmospheric conditions: 5% CO2, O2-enriched 5% CO2, and anaerobic. Strain UA159 was tested for biofilm formation in the presence or absence of manganese under anaerobiosis. S. mutans GS-5 did not survive in manganese-depleted media. Strains UA159, UA130, 3209 and Ingbritt showed a decrease in population density when grown in manganese-depleted media. Strains UA159, UA130, 3209 and Ingbritt showed a decrease in population density when grown in manganese-depleted medium in CO2. Furthermore, strain 3209, LT11 and ATCC 25175 did not multiply in an O2-enriched 5% CO2 atmosphere. When cultured in an anaerobic environment, the UA159, UA130, 3209 and Ingbritt strains showed significant growth in manganese-depleted media, whereas strains LT11 and ATCC 25175 grew poorly. Strain UA130 was affected the least by manganese deprivation. Strain variability was also observed in the presence of high levels of manganese. Both sucrose-dependent and – independent biofilm architectures were affected by the absence of manganese. A microarray analysis suggested the potential for manganese effects on virulence genes whose products mediate adherence and interactions with glucans. Selected virulence genes were investigated by performing northern blots, western blots, and reverse transcriptase polymerase chain reaction under conditions of planktonic and biofilm growth in manganese-depleted media or in media containing 50 µM manganese. Manganese-depleted conditions resulted in decreased expression of gbpC and gtfB, and increased expression of wapA, in both planktonic and biofilm cultures. The expression levels of gbpA and gbpD were enhanced in the manganese-depleted state, but only in biofilm cultures. The expression of gtfC was reduced in the absence of manganese only in planktonic dultures. The spaP gene was expressed less in manganese-depleted planktonic dultures but expressed more highly in manganese-depleted biofilm cultures. These results suggest that manganese levels may influence colonization with particular strains of S. mutans. And/or its overall cariogenic potential. It can be concluded that manganese availability affects the expression of S. mutans virulence genes and that these effects depend on the growth state of the organism.