The lipase LipA (PA2862) but not LipC (PA4813) from Pseudomonas aeruginosa influences regulation of pyoverdine production and expression of the sigma factor PvdS

Abstract

A key element in iron-dependent regulation of iron metabolism and virulence-related functions for Pseudomonas aeruginosa is the sigma factor PvdS. PvdS expression itself is also influenced by iron-independent stimuli. We show that pyoverdine production and pvdS expression depend on one of the two lipases of P. aeruginosa.

Fig. 1.

Pyoverdine concentrations in P. aeruginosa culture supernatants. (A) Wild-type (WT), ΔpvdS mutant, ΔlipA ΔlipC double mutant, and the double mutant with a lipA or lipC expression plasmid, which also harbored the gene for the lipase-specific chaperone lipH for proper folding of the lipases, were grown for 8 h at 37°C in M9 minimal medium without iron supplementation, and pyoverdine concentrations were determined in cell-free supernatants (9). (B) The wild type and a ΔlipA mutant harboring the empty vector (ev) or a lipA expression plasmid were grown in rich LB or minimal M9 medium, and the relative pyoverdine concentrations were determined after 8 h of growth.

Fig. 2.

Change in gene expression of pvdS in a P. aeruginosa ΔlipA mutant relative to the wild type (light gray). The right side of the graph compares (based on the fold change) the regulation of pvdS and PvdS-regulated genes (pvdD, pvdE, and prpL) in a ΔlipA mutant with empty vector (ev) versus a ΔlipA mutant which harbored the lipA gene and the gene for the lipase-specific chaperone lipH on plasmid pVLT33-LipAH (lipAH; dark gray). In all cases transcription was normalized to rpoD. Cultures were grown for 8 h in LB medium at 37°C before RNA was isolated. Error bars represent standard deviations from three independent experiments.