fragilis does not

significantly increase the presence of DNA strand breaks. This is in contrast to what was observed in a B. fragilis recA mutant, where the absence of the RecA protein led to an increase in the presence of single- and double-strand breaks in DNA (Steffens et al., 2010). The recQ mutant strains showed varying levels of increased sensitivity to metronidazole (Table 2). At 60 min, the wild type survived 1.32-fold, 41.88-fold and 23.18-fold better than mutants RecQ1, RecQ2 and RecQ3, respectively. These results confirmed that these proteins are needed for cell survival following metronidazole damage in B. fragilis, although their exact roles have not yet been elucidated. The extreme sensitivity of strain RecQ2 to metronidazole highlights the fact that the absence of this particular homologue (and/or the downstream Tpr protein) causes significant stress in the bacterium, as evidenced check details by elongated cells and defective growth. The E-test results confirmed that the mutants were more sensitive to metronidazole, with B. fragilis minimum inhibitory concentration values of

0.25 μg mL−1 for strain 638R, compared with 0.125 μg mL−1 for strains RecQ1 and RecQ3, and <0.016 μg mL−1 for RecQ2. This suggests that a RecA-positive background supports metronidazole damage repair in the absence of RecQ1 and RecQ3, but is insufficient in the absence of RecQ2 and possibly its downstream gene product. In this Tau-protein kinase study, it ABT-199 cell line has been shown that mutations in the RecQ helicases

render B. fragilis more sensitive to metronidazole and that these proteins are, therefore, important for the cellular response to metronidazole-induced cell damage. The most sensitive mutant strain, RecQ2, exhibited severe growth defects, defective cell division and aberrant cell morphology, possibly due to polar effects on ORF638R_3782, which encodes a putative TPR protein and may be implicated in cell division. Further studies are needed to establish the precise function of each RecQ homologue in maintaining B. fragilis viability following metronidazole challenge. This study was supported by grants from the Wellcome Trust (070375/Z/03/Z), the South African Medical Research council and a South Africa–Sweden Collaborative Research Grant (through the National Research Foundation). C.E.N. acknowledges a grant from the Swedish Research Council (348-2006-6862). We thank A.A. Salyers and N.B. Shoemaker (Urbana, IL) for providing the pLYL01 and pGERM plasmids, and acknowledge G. Blakely for useful discussions. Fig. S1. Confirmation of insertional mutation of recQ genes. Fig. S2. Visualization of Bacteroides fragilis cells using fluorescence microscopy. Fig. S3. Visualization of DNA double- and single-strand breaks. Table S1. Primers used in this study. Table S2. RecQ homologues from the Bacteroides groupNB.