Figure 2From: Lipopeptide biosynthesis in Pseudomonas fluorescens is regulated by the protease complex ClpAP Phenotypic and chemical analyses of P. fluorescens strain SS101, and its clpA mutant. (A) Drop collapse assay with cell suspensions of wild-type strain SS101, clpA plasposon mutant, clpA mutant + pME6031 (empty vector control) and clpA mutant + pME6031-clpA. Bacterial cultures grown for 2 days at 25°C on KB agar plates were suspended in sterile water to a final density of 1x1010 cells/ml. 10-μl droplets were spotted on parafilm and crystal violet was added to the droplets to facilitate visual assessment. A flat droplet is a highly reliable proxy for the production of the surface-active lipopeptide massetolide A. (B) RP-HPLC chromatograms of cell-free culture extracts of the wild-type strain SS101, clpA plasposon mutant, clpA + pME6031 (empty vector control) and clpA + pME6031-clpA as described in panel A. The wild-type strain SS101 produces massetolide A (retention time of approximately 23–25 min) and various other derivatives of massetolide A (minor peaks with retention times ranging from 12 to 18 min) which differ from massetolide A in the amino acid composition of the peptide moiety. (C) Swarming motility of the wild-type strain SS101, clpA plasposon mutant, clpA mutant + pME6031 (empty vector control) and clpA mutant + pME6031-clpA on soft (0.6% wt/vol) agar plates. Five microliter (1×1010 cells/ml) of washed cells from overnight cultures was spot-inoculated in the center of a soft agar plate and incubated for 48–72 h at 25°C. (D) Growth of the wild-type SS101 strain, clpA plasposon mutant, clpA mutant + pME6031 (empty vector control), clpA mutant + pME6031-clpA and clpP site-directed mutagenesis mutant in liquid medium at 25°C. The optical density of the cell cultures was measured spectrophotometrically (600 nm) at different time points. Mean values of four biological replicates are given; the error bars represent the standard error of the mean.Back to article page