The Stringent Response Controls Catalases in Pseudomonas aeruginosa and Is Required for Hydrogen Peroxide and Antibiotic Tolerance

Abstract

e Pseudomonas aeruginosa, a human opportunistic pathogen, possesses a number of antioxidant defense enzymes under the control of multiple regulatory systems. We recently reported that inactivation of the P. aeruginosa stringent response (SR), a starvation stress response controlled by the alarmone (p)ppGpp, caused impaired antioxidant defenses and antibiotic tolerance. Since catalases are key antioxidant enzymes in P. aeruginosa, we compared the levels of H 2 O 2 susceptibility and catalase activity in P. aeruginosa wild-type and ⌬relA ⌬spoT (⌬SR) mutant cells. We found that the SR was required for optimal catalase activity and mediated H 2 O 2 tolerance during both planktonic and biofilm growth. Upon amino acid starvation, induction of the SR upregulated catalase activity. Full expression of katA and katB also required the SR, and this regulation occurred through both RpoSindependent and RpoS-dependent mechanisms. Furthermore, overexpression of katA was sufficient to restore H 2 O 2 tolerance and to partially rescue the antibiotic tolerance of ⌬SR cells. All together, these results suggest that the SR regulates catalases and that this is an important mechanism in protecting nutrient-starved and biofilm bacteria from H 2 O 2 -and antibiotic-mediated killing.

Starvation- and antibiotics-induced formation of persister cells in Pseudomonas aeruginosa

“…Other mechanisms such as the development of swarming colonies, the stringent response, i.e. response to nutrient limitation, and the formation of multiresistant subpopulation of persistent cells contribute to the multidrug-resistant phenotype [21][22][23] . Furthermore, P. aeruginosa is versatile in the development or acquisition of new mechanisms of resistance to antibiotic treatment.…”

“…Regarding stringent response, for P. aeruginosa and E. coli growing in biofilms it was found that stringent response was necessary for maintaining the low levels of reactive oxygen species (ROS) (ref. 12,13 ) which are associated with apoptosis-like death 14 . Furthermore, Aizenman and coworkers described that overexpression of ppGpp induced mazEF death pathway through the stable toxin MazF which is able to exert its deleterious effects and cause cell death 15 .…”

Silver-coated carbon nanotubes downregulate the expression of Pseudomonas aeruginosa virulence genes: a potential mechanism for their antimicrobial effect

“…A reduced expression of rpoS in the presence of AgCNTs in both strains may suggest a decreased ability for survival under stress imposed by AgCNTs, whereas an increased expression in the presence of gentamicin may suggest the opposite. It is known that the general oxidative stress regulator and alternative sigma factor, RpoS 35 regulates the expression of more than 35 genes, many of which are involved in the general stress response. RpoS also plays a role as an intermediary regulator of catalase activity and hydrogen peroxide (H 2 O 2 ) tolerance.…”

Biofilm-Related Infections: Bridging the Gap between Clinical Management and Fundamental Aspects of Recalcitrance toward Antibiotics

“…Furthermore, in P. aeruginosa, the stringent response is required for optimal catalase activity and mediates H 2 O 2 tolerance during both planktonic and biofilm growth. Upon amino acid starvation, induction of the stringent response upregulates catalase activity (119). The demonstration of a link between the stringent response and oxidative stress defense is interesting, as ROS have been proposed to explain antibiotic-induced bacterial cell death (120)(121)(122).…”