FIGURE 3.

⁵⁴Mn accumulates in S. mutans GMS3000, an SMU_1176 insertion-deletion mutant. Intracellular concentrations of ⁵⁴Mn were significantly greater in GMS3000 compared to those in UA159, GMS284, and GMS3001, consistent with a role for the SMU_1176 gene product as Mn²⁺ efflux protein. Overnight cultures of UA159, GMS284, GMS3000, and GMS3001 were normalized to ±0.005A, and grown in the presence of ⁵⁴Mn (experimental) or 0.5 M HCl (control) for 16–18 hr. The cell pellets and supernatants were separated by centrifugation, and counts per minute (CPM) were determined by liquid scintillation counting. The number of colony forming units (CFUs) was determined by plating serial dilutions of the control cultures in parallel. The CPM of the cell pellets were divided by the CPM of the supernatants, and that value was divided by the number of CFUs to normalize the ⁵⁴Mn transport data. Error bars denote the standard deviation about the mean. Variation in the experimental design includes some inevitable loss of cell associated ⁵⁴Mn during the wash steps. Nevertheless, ANOVA analysis with Tukey’s test revealed significant differences between GMS3000 and each of the other three test strains (p < .01). N = 3