Spontaneous mutation rates of error-prone polymerase deletion mutant and control strains. Mutation rates were determined by the fluctuation analysis of D-cycloserine-resistant mutants . Gene names are indicated for the single-deletion strains, while MDS42pd, MDS42pu, MDS42du, and MDS42pdu denote MDS42polBdinB, MDS42polBumuDC, MDS42dinBumuDC, and MDS42polBdinBumuDC, respectively. Error bars represent 95% confidence intervals for the average of 4 independent measurements. ANOVA revealed a significance of p < 0.005. Pairwise t-tests were conducted for each strain compared to the MDS42 strain, * indicates a significance of p < 0.05, ** indicates a significance of p < 0.01, *** indicates a significance of p < 0.001.