Figure 2 HPLC analysis of the degradation of 3-oxo-C6-D-HSL after incubation with Acinetobacter GG2 and Burkholderia GG4. (A) The D-isomer of GSK1120212 cost 3-oxo-C6-HSL was incubated BVD-523 for 0- (blue line), 3- (black line) and 24 h (grey line) with GG2, the culture supernatant extracted with ethyl acetate and subjected to HPLC analysis. The data show the disappearance of the AHL peak at 5.0

min after 24 h incubation. (B) When incubated with GG4 over a period from 0- (red line), 3- (blue line) and 24 h (black line), the 3-oxo-C6-D-HSL peak is replaced by a new peak at about 4.3 min which co-migrates with 3-hydroxy-C6-HSL. The controls used were synthetic 3-oxo-C6-D-HSL, 3-hydroxy-C6-D-HSL (green line) and PBS buffer incubated with GG4 for

24 h to ensure no 3-hydroxy-C6-HSL production by GG4 (purple line). (C) MS showing the presence of 3-oxo-C6-HSL at 0 h (upper panel; m/z 214.2 [M+H]) and 3-hydroxy-C6-HSL after 24 h (lower panel; m/z 216.2 [M+H]) when 3-oxo-C6-L-HSL was incubated with GG4. Identification of the AHL degradation products To determine whether Acinetobacter strain GG2 inactivated AHLs through cleavage of the acyl chain or via lactonolysis or both, 3-oxo-C6-HSL was first incubated with GG2 cells for 24 h. The cells were removed and the supernatant was collected, acidified to pH 2 and incubated for a further 24 h. This results in the pH-mediated re-cyclization of any ring opened compound present [8] which was subsequently detected using the XAV939 C. violaceum CV026 AHL biosensor [15]. Figure 1 shows that while no 3-oxo-C6-HSL was detected filipin in the supernatant after 24 h incubation with GG2, it could be recovered by acidification indicating that GG2 possesses lactonase activity. To investigate whether GG2 also exhibits amidase activity a cell-free GG2

24 h culture supernatant grown in the presence of 3-oxo-C6-HSL was treated with dansyl chloride which reacts with the exposed free amine of the homoserine lactone ring following release of the AHL acyl chain [16]. No dansylated homoserine lactone was detected indicating that GG2 does not exhibit acylase activity (data not shown). Similar acidification experiments to those described above for Acinetobacter GG2 were carried out for Klebsiella Se14. These showed that Se14 also possesses a lactonase. Since Klebsiella pneumoniae has previously been reported [11] to possess a homologue of the Arthrobacter lactonase gene ahlD termed ahlK, we used primers based on ahlK to determine whether the gene was also present in Se14. A single PCR product was obtained and sequenced and found to be identical to the ahlK gene (data not shown). When Se14 ahlK was expressed in E.