Colonies were counted after 48 h of incubation at 28 °C. The survival percentage was defined as the number of CFU recovered after the treatment divided by the number of CFU before treatment multiplied by 100. Cu resistance was selleck determined as described previously, with some modifications

(Sukchawalit et al., 2005). Briefly, CuSO4 at a final concentration of 1 mM was added to an exponential-phase culture of Xcc. The culture was further incubated for 1 h with continuous shaking. In antioxidant protection experiments, 1 mM α-tocopherol, 10 mM pyruvate, and 1.0 M glycerol were added to bacterial cultures 10 min before the addition of CuSO4. The number of surviving cells was determined using viable plate counts and expressed as per cent survival. The insertional inactivation of ahpC (xcc0834, da Silva et al., 2002) was achieved using the pKNOCK suicide vector system (Alexeyev, 1999). An ahpC gene fragment was PCR amplified using BT2684 (5′-CGCAGCGTCTCGGTGACG-3′) and BT2685 (5′-AGTGGAAGACGCCGCTGA-3′) oligonucleotide primers and Xcc genomic DNA as a template. The 300-bp PCR product find more was cloned into pGem-T-easy (Promega) and then an EcoRI fragment was subcloned into pKNOCK-Km cut with the same enzyme to generate pKNOCKahpC. The recombinant plasmid was electroporated subsequently into wild-type Xcc. The

mutant, which was selected for its kanamycin resistance phenotype, was confirmed by Southern blot analysis using an ahpC-specific probe (data not shown). The pAhpC plasmid used for the plasmid-borne expression of ahpC was constructed by PCR amplification of full-length ahpC using BT3026 (5′-CAGGGATGCGAGGCGGCT-3′) and BT3027 (5′-AGGAAACTCAATGTCTCT-3′)

primers. PCR was performed using Pfu DNA polymerase with proofreading activity (Promega), and the product was directly cloned into the broad-host-range plasmid vector, pBBR1MCS-4 (Kovach et al., 1995), at the EcoRV site, to form pAhpC. The ahpC gene was expressed in Xanthomonas under the control of the lacUV5 promoter of the vector. Exposure of an exponential-phase culture of Xcc to 50 mM tBOOH for 30 min resulted in roughly 10% survival compared with the untreated Avelestat (AZD9668) culture (Fig. 1). The effect of Cu ions in tBOOH killing was investigated. CuSO4 at concentrations below 0.5 mM exerted no adverse effects on Xcc growth in rich medium (SB). The addition of 100 μM CuSO4 to the tBOOH killing treatment resulted in a 100-fold decrease in the per cent survival compared with only tBOOH treatment (Fig. 1). The enhanced killing effect of tBOOH by CuSO4 was abolished by the addition of the Cu chelator, bathocuproine sulphonate, at a final concentration of 200 μM (Fig. 1). Generally, organic hydroperoxide toxicity is a result of lipid peroxidation reactions (Farr & Kogoma, 1991).