Both Bxy-CTL-1 and Bxy-CTL-2 were predicted as non-secretory peroxisomal proteins. However, according to Shinya et al.[31], Bxy-CTL-2 was secreted after pine wood extract stimulation. BlastP search for both catalases retrieved very similar orthologous catalases (62-64% maximum identity and e-value 0.0) from different species of Caenorhabditis and other animal parasitic

nematodes, suggesting the catalases are GANT61 purchase conserved among the phylum Nematoda (Additional file 1: Figure S1 and Additional file 2: Figure S2). The relative gene expression of catalase genes of B. xylophilus Ka4 and C14-5 with or without Serratia spp. PWN-146 was studied under stress conditions (Figure 4). After Cisplatin concentration 24 h exposure to 15 mM H2O2, the expression levels of Bxy-ctl-1 and Bxy-ctl-2 genes in the B. xylophilus Ka4 and C14-5 were measured (Figure 4A and 4B). While virulent Ka4 catalases (Bxy-ctl-1

and Bxy-ctl-2) were significantly (p < 0.05 and p < 0.01, respectively) up-regulated by nearly 2-2.5-fold compared to the non-stress condition (Figure 4A) The expression of Bxy-ctl-1 in the avirulent C14-5 was unchanged and the expression of Bxy-ctl-2 was slightly reduced (p < 0.05) (Figure 4B). These results seem to support the observations denoted in Figure 2. In the presence of the associated bacteria Serratia spp. PWN-146, the relative Sepantronium cell line expression of Ka4 Bxy-ctl-1 was highly suppressed (p < 0.01), nearly 0.5-fold less than under non-stress conditions. Under the same conditions, Ka4 expression of Bxy-ctl-2 was not affected. The expression levels of both catalases in the avirulent C14-5 showed no significant induction or suppression. In the presence of control strain E. coli OP50, the expression level of Bxy-ctl-1 in the Ka4 was induced four-fold under stress conditions, and Bxy-ctl-2

expression level remained unchanged under non-stress conditions. Similar result was obtained for C14-5, in which E. coli OP50 induced 5 times more Bxy-ctl-1 expression under stress conditions, explaining the results many obtained in Figure 2. The expression levels of Bxy-ctl-2 were also induced (p < 0.05), nearly 1.5-fold (Figure 4B). Figure 4 Relative gene expression changes of Bxy-ctl-1 and Bxy-ctl-2 H 2 O 2 treatment for 24 h. Bursaphelenchus xylophilus Ka4 (virulent) and C14-5 (avirulent) with and without bacteria (A and B) (Serratia spp. PWN-146 and E. coli OP50). *p < 0.05; ** p < 0.01, compared to a normalized value of 1.00 for control nematode without H2O2. Discussion Tolerance to host-mediated OS is an essential characteristic of plant-associated organisms. In this study, we tested if B. xylophilus-associated bacteria could tolerate prolonged oxidative stress conditions with or without the nematode, in an attempt to understand their behaviour in the oxidative burst conditions of the host tree in the early stages of PWD.