Data represent the mean from three independent experiments, ± one standard deviation. Catabolic repression of aromatic compound degradation by TCA intermediates and glucose has been described in the β-proteobacterium Acidovorax sp. [29], and P. putida [15] respectively. In accordance

with these data we found that the PA catabolic pathway of B. cenocepacia K56-2 is subject to catabolic repression by glucose and succinate (Figure 3). Interestingly, P paaA is induced after 18 h of growth in SCFM probably as a result of the presence of phenylalanine (Figure 2). This observation is consistent with the recently reported B. cenocepacia global gene expression 17-AAG ic50 response to SCFM, which shows the induction of the PA catabolic pathway [30]. Whether this finding is relevant for pathogenesis of Bcc in NU7441 in vivo the CF lung environment remains an unexplored point of interest. Conclusion We show that the PA gene promoters are responsive to PA, SCFM, and other compounds expected to proceed via the PA pathway. We also show the PA gene promoters are negatively regulated by PaaR, a TetR-type regulator, and are subjected to catabolic repression by succinate and glucose. Methods Bacterial strains, nematode strains and growth conditions Bacterial strains and plasmids are listed in Table 1. B. cenocepacia K56-2 was grown at 37°C in Luria Bertani (LB) or M9 minimal medium with 5 mM PA or 25 mM of the

indicated carbon sources, supplemented as required, with 100 μg/ml trimethoprim (Tp), Etoposide 50 μg/ml gentamicin (Gm) and 200 μg/ml chloramphenicol (Cm). E. coli was grown at 37°C in LB medium supplemented with 50 μg/ml Tp, 40 μg/ml kanamycin (Km) or 20 μg/ml Cm. Reporter

activity assays 96-well microplates containing 150 μl of M9 minimal media supplemented with indicated carbon source(s) were inoculated with 2 μl from an overnight culture grown in LB, washed with PBS and adjusted to an O.D. 600 of 2.0 with M9 minimal salts. 96-well microplates were incubated at 37°C with shaking at 200 rpm. eGFP protein has excitation/emission wavelengths of 488/509 [31]. Relative fluorescence, defined as the ratio between arbitrary fluorescence and optical density at 600 nm (O.D.600) was measured with a Biotek Synergy 2 plate reader, using excitation 485/20 and emission 528/20 filter sets. O.D. 600 values were converted to 1 cm path length O.D. 600 using a standard curve. Bioinformatics analysis BLAST searches of the genome sequence of B. cenocepacia strain J2315 were performed with the B. cenocepacia Blast Server at Sanger Institute http://​www.​sanger.​ac.​uk/​cgi-bin/​blast/​submitblast/​b_​cenocepacia. J2315 belongs to the same clonal lineage as strain K56-2 [32]. Gene clusters were visualized with Artemis software [33] and VectorNTI software (Invitrogen). PWM scores were calculated manually [25] (Additional file 2) as described by Hertz and Stormo [34] and Schnieder and Stephens [35]. Identification of binding sites using this PWM was achieved using the Target Explorer [36].