1b). Because of the highly conserved nature of the nucleotide sequence of the helicase domain, specific primers were designed to unique regions of the helicase domains of the three genes to ensure amplification of the correct gene target. This strategy resulted in the interruption

of the helicase domain as well as its separation from the RecQ C-terminal and HRDC domains. Mutations were confirmed by PCR and sequencing of the products generated by the mutants (Fig. BIBW2992 S1). Growth comparison of B. fragilis 638R wild type and the three mutants showed that mutant RecQ2 exhibited reduced growth after 8 h (OD600 nm=0.5) as compared with the other strains (OD600 nm=0.8). Gram staining (Fig. 3a) and TEM of ultrathin sections (Fig. 3b)

revealed that strain RecQ2 was considerably more pleiomorphic than the wild type, displaying extensive elongation (10–20 μm) (Fig. 3b, iv) as compared with the wild type (1–5 μm) (Fig. 3b, i). Chains of short cells were also seen in RecQ2 (Fig. 3b, v), suggesting that the cells did not separate to completion possibly due to a defect in cell division. It is well known that wild-type B. fragilis is intrinsically pleiomorphic and that elongated cells or filaments of attached cells are occasionally seen even in wild-type cultures (Jousimies-Somer et al., 2002). The genetic and biological reasons for this are not known. Cells with mutated recQ2 show an increase in the frequency of this phenomenon and point to an JQ1 involvement of this RecQ protein in the cell-division process. The phenomenon of elongation, abnormal growth and defective septa formation was reported previously in B. fragilis cells grown in the presence of low doses of clindamycin and cephalosporins (Fang

et al., 2002; Silvestro et al., 2006). It is important to note here that the interruption of recQ2 could affect the transcription of tpr, the third gene in the recJ-recQ2-tpr operon, and hence influence the phenotype. Cells were stained with DAPI to investigate whether the double-stranded integrity of the genetic material in the RecQ2 mutant was affected, and Dolutegravir the cell membranes were further stained with FM4-64 to visualize the individual cell boundaries. Fluorescence microscopy of the stained cells confirmed the Gram stain and TEM results. The cells of the wild type, mutant RecQ1 and mutant RecQ3 had a similar appearance (short individual rods with a compact chromosome), whereas the filaments of mutant RecQ2 consisted of chains of long and short cells that failed to separate into single cells (Fig. S2). All strains showed equivalent fluorescence intensity of the DAPI stain, indicating equivalent amounts of double-stranded DNA. DNA from the strains was further analysed by standard and alkaline gel electrophoresis to detect the presence of single- and double-strand breaks (respectively), but no difference could be observed between the mutants and the wild-type strains (Fig. S3).