, 2002) In a similar manner, RhlI is responsible for the generat

, 2002). In a similar manner, RhlI is responsible for the generation of the signal molecule C4-HSL, which binds to its receptor RhlR

and activates the transcription of its target genes, many of which are involved in the production of secondary metabolites, such as pyocyanin (Pesci & Iglewski, 1997). According to the current knowledge, acyl homoserine lactone (AHL) signals, like 3O-C12-HSL and C4-HSL mentioned in the QS systems, are produced from acyl enoyl-acyl carrier proteins (acyl-ACPs) and S-adenosylmethionine (More et al., 1996), where the acyl-ACPs are intermediates in the fatty acid biosynthesis pathway (Schaefer et al., 2000). One well-characterized enoyl-CoA reductase, high throughput screening assay FabI, plays an important role in the fatty acid biosynthesis, like regulating the proportion of the saturated to unsaturated fatty acids, coordinating fatty acid and phospholipid syntheses, and controlling the elongation of fatty acid (Heath & Rock, 1995). Furthermore,

check details FabI has been implicated in providing an acyl group in the synthesis of AHLs (Hoang & Schweizer, 1999). In our previous work, the product of the PA2950 gene (we named it pfm) was shown to affect the swimming mobility of P. aeruginosa. This was not attributable to the lack of intact flagellum production but to the loss of its ability to rotate (Bai et al., 2007). Recently, pfm was shown to encode an enoyl-CoA reductase, which also participates in the fatty acid biosynthesis (Zhu et al., 2010), similar to that of FabI. In this report, we show

that pfm influences the QS system through the production of AHL molecules, and disruption of the pfm gene results in decreased bacterial ability to adhere to host cells and a delayed killing of Caenorhabditis elegans. Escherichia coli and P. aeruginosa were cultured in Luria–Bertani medium at 37 °C. Antibiotics were used as follows: for E. coli, 50 μg mL−1 ampicillin, 25 μg mL−1 kanamycin, and 25  μg mL−1 tetracycline; for P. aeruginosa, 50 μg mL−1 kanamycin, 100 μg mL−1 tetracycline, and 300 μg mL−1 carbenicillin. P. aeruginosa strains PA68 (a clinical isolate) and PA68 pfm::Mu (KmR) (named I69) have been described previously (Bai et al., 2007). The biosensor strain JB525 was provided by FER Dr Liang Yang, Technical University of Denmark (Wu et al., 2000). The assay for bacterial adherence to a human cell line was performed as described previously (de Bentzmann et al., 2006). Human lung cell line A549 was cultured in DMEM medium with 10% FBS. Before infection, the medium was replaced with serum and antibiotic-free medium. Then, cells were incubated at 37 °C for 4 h. Bacteria were then added into the cultured cells at a multiplicity of infection (MOI) of 30 for 1 h. Cells were washed twice with PBS, fixed with 4% formaldehyde, and then washed twice with PBS again. The fixed cells were stained with 0.1% crystal violet for 5 min, washed with PBS, and observed with Axioscop 40 microscope.

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