No significant hits were obtained with the AHL lactonase aiiA sequence
[35]. However, the aac gene encodes a putative protein that was defined as a probable aculeacin A acylase transmembrane protein (NP 520668). Among selleck the function-demonstrating proteins, Aac shared 83%, 39%, 24%, and 24% identities at the peptide level with the AHL-acylase from Ralstonia sp. XJ12B [14], aculeacin A acylase from Actinoplanes utahensis [38], cephalosporin acylase from Brevundimonas diminuta [39], and Penicillin G acylase from Providencia rettgeri [40], respectively. Cloning and expression of the aac gene of R. solanacearumGMI1000 The aac gene was PCR amplified (refer to Materials and Methods) and the 2,405 bp product was cloned in pBBR1MCS-3 to yield plasmid pS3aac. To analyse the ability of Aac to degrade AHLs pS3aac was used to transform E. coli DH10B. The cloned aac sequence was confirmed to have no mutations. For examining the degrading activity of the clone E. coli DH10B (pS3aac), C6-, C7-, and
C8- HSLs were used as autoinducers in performing a whole cell bioassay described selleck products in the Materials and Methods. The results of the whole cell bioassay revealed that E. coli DH10B (pS3aac) cells were inactive BTK inhibitor against C6-HSL while active against C7- and C8-HSLs (Table 2). Since the vector pBBR1MCS-3 does not contain lacI, we considered that E. coli DH10B (pS3aac) cells exhibit C7- and C8-HSLs AMP deaminase degrading activities inrespective of the presence or absence of IPTG induction (Table 2). Because C7-HSL was a more sensitive AHL than C8-HSL (data not shown), we chose C7-HSL for inducing C. violaceum CV026 to produce violacein in whole cell bioassay (Fig. 1, well 1). The cells of E. coli DH10B (pS3aac) exhibited C7-HSL degrading activity (Fig. 1, well 3), while no activity was observed in the cell-free culture supernatant of E. coli DH10B (pS3aac) (Fig. 1, well 4). This data indicated that the protein
encoded by the aac gene is a cell associated AHL-degrading enzyme. The aac gene was fused into pET21a to yield plasmid pET21aac, and then over expressed in E.coli BL21(DE3) from an inducible promoter. The SDS-PAGE analysis demonstrated that the IPTG-induced total proteins contained a polypeptide with a molecular mass of 88 kDa that was consistent with the 824 residues Aac-fused protein that had a predicted molecular mass of 88,645 Da (Fig. 2). Table 2 The AHL-degrading abilities of E. coli DH10B (pS3aac) evaluated by whole cell bioassay AHL-degrading abilitiesa C6-HSL C7-HSL C8-HSL Test strains IPTG(+) IPTG(-) IPTG(+) IPTG(-) IPTG(+) IPTG(-) C S C S C S C S C S C S E. coli DH10B (pBBR1MCS-3) – - – - – - – - – - – - E.
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