violaceum CV026, was used as a target microorganism. The mutant LY3023414 mw C. violaceum CV026 cannot produce violacein unless provided with exogenous AHL . Therefore the pS3aac was transformed into C. violaceum CV026 to observe whether violacein production was reduced during culture with exogenous
AHL. As shown in Fig. 4A, the result indicates that the expression of the aac gene did not influence the growth of C. violaceum CV026 during the late exponential phase but slightly influenced its growth during the stationary phase. Interestingly, C. violaceum CV026 (pBBR1MCS-3) produced violacein after the late exponential phase, while C. violaceum CV026 (pS3aac) completely failed in producing violacein (Fig. 4B). Since it was reported that chitinases could be regulated by endogenous C6-HSL
in C. violaceum ATCC 31532 , we selleckchem decided to evaluate the chitinolytic activity of C. violaceum CV026 (pS3aac). C. violaceum CV026 (pBBR1MCS-3) was able to form clear zones on LB agar containing tetracycline, chitin, and C7-HSL. However, no clear zone were observed around the C. violaceum CV026 (pS3aac) colonies (Fig. 4C). These results indicated that transferring the aac gene into C. violaceum CV026 significantly inhibited violacein production and chitinase activity. Figure 4 The effects of Aac on the production of violacein and chitinase activity in C. violaceum CV026. The plasmids pBBR1MCS-3 and pS3aac were transformed into C. violaceum CV026. Both of them were cultivated in LB containing tetracycline OSI-027 order as well as 25 μM C7-HSL. (a) Cell growth was Celastrol monitored by measuring the OD600. (b) The violacein production was determined by OD576 during growth. The data represent the mean values of three independent experiments. (c) The overnight cultures of C. violaceum CV026 (pS3aac) and C. violaceum CV026 (pBBR1MCS-3) (no aac insert) were seeded onto an LA plate containing tetracycline, C7-HSL and chitin in order to assay the chitinolytic activity. The plates were incubated at 30°C for 5 d. The formation of a clear zone around
the colonies indicated positive chitinolytic activity. Discussion We successfully subcloned and identified an aac gene (NP 520668) from R. solanacearumGMI1000 as an AHL-acylase that did not degrade aculeacin A, ampicillin, and ceftazidime (data not shown). The amino acid sequence of Aac is similar to that of AHL-acylase from Ralstonia sp. XJ12B (Ralstonia eutropha) with 83% identity. However, this is the first study to report the presence of an AHL-acylase in a phytopathogen. To verify the existence of an AHL-acylase, both gas chromatography assays  and HPLC-ESI-MS analyses [13, 14] are generally used to analyse the digested AHL products. Our report provides a simple and rapid ESI-MS analysis to verify AHL-acylase.