Microarray analysis and functional characterization of the nitrosative stress response in nonmucoid and mucoid Pseudomonas aeruginosa

Abstract

The type strain of Pseudomonas aeruginosa, PAO1, showed great upregulation of many nitrosative defense genes upon treatment with S-nitrosoglutathione, while the mucoid strain PAO578II showed no further upregulation above its constitutive upregulation of nor and fhp. NO* consumption however, showed that both strains mount functional, protein synthesis-dependent NO*-consumptive responses.

FIG. 1.

Correlation between denitrification reaction pathway and increases in gene expression resulting from nitrosative stress, based on microarray data (see Table S1 in the supplemental material).

FIG. 2.

NO^· consumption by P. aeruginosa strains PAO1 and PAO578II (in the presence of 0.3 M NaCl) measured with an NO^· electrode after nitrosative stress; data shown are means + 1 standard deviation (n = 8). Nitrosative stress consisted of exposure to GSNO (initial concentration, 5 mM) for 0 to 45 min, after which the bacteria were centrifuged and resuspended in GSNO-free LB medium. Consumption rates for PAO1 (except at time zero) were all statistically significant compared to those of either the same strain at time zero or the other strain at the same time point at a P value of <0.01 (t test).

FIG. 3.

Effect of protein synthesis inhibition by tetracycline (50 μg/ml) on NO^· consumption by P. aeruginosa PAO1 and mucoid strain PAO578II as measured with an NO^· electrode after nitrosative stress; data shown are means + 1 standard deviation (n = 4). Nitrosative stress consisted of exposure to GSNO (initial concentration, 5 mM) for 0 to 45 min, after which the bacteria were centrifuged and resuspended in GSNO-free LB medium still containing tetracycline. Consumption rates were analyzed as percentages of the initial GSNO-free rate, and all data points for strains PAO1 and PAO578II with or without tetracycline (except at time zero) were statistically significant at a P value of <0.01 (t test).