FIG 4.

Targeted mutations of recA in P. micra. (A) The recA deletion construct (top) was inserted into the P. micra A28 chromosome through homologous recombination (middle), resulting in allelic replacement of the recA ORF with an ermB cassette (bottom). (B) A recA knock-in mutagenesis construct (top) was inserted into the P. micra chromosome through homologous recombination (middle), resulting in the insertion of the recA ORF and aphAIII cassette downstream of EF-Tu (bottom). The ΔrecA mutation was complemented by moving this mutation into the recA knock-in background. (C) Transformation frequency of wild-type A28 (WT), A28 ΔrecA mutant (ΔA), double recA-expressing knock-in mutant (+A), and complemented ΔrecA mutant (+A/ΔA). Transformation frequency is expressed as the ratio of rifampin-resistant bacteria to total CFU. (D) Mitomycin C survival curves. All values are averaged from triplicate independent determinations ± SD. For transformation assays, comparisons are indicated by brackets. For MMC experiments, comparisons are presented relative to ΔA. Statistical analysis was performed using a two-tailed Student’s t test. *, P < 0.05.