Influence of RpoN on isocitrate lyase activity in Pseudomonas aeruginosa

Abstract

Pseudomonas aeruginosa is the major aetiological agent of chronic pulmonary infections in patients with cystic fibrosis (CF). The metabolic pathways utilized by P. aeruginosa during these infections, which can persist for decades, are poorly understood. Several lines of evidence suggest that the glyoxylate pathway, which utilizes acetate or fatty acids to replenish intermediates of the tricarboxylic acid cycle, is an important metabolic pathway for P. aeruginosa adapted to the CF lung. Isocitrate lyase (ICL) is one of two major enzymes of the glyoxylate pathway. In a previous study, we determined that P. aeruginosa is dependent upon aceA, which encodes ICL, to cause disease on alfalfa seedlings and in rat lungs. Expression of aceA in PAO1, a P. aeruginosa isolate associated with acute infection, is regulated by carbon sources that utilize the glyoxyate pathway. In contrast, expression of aceA in FRD1, a CF isolate, is constitutively upregulated. Moreover, this deregulation of aceA occurs in other P. aeruginosa isolates associated with chronic infection, suggesting that high ICL activity facilitates adaptation of P. aeruginosa to the CF lung. Complementation of FRD1 with a PAO1 clone bank identified that rpoN negatively regulates aceA. However, the deregulation of aceA in FRD1 was not due to a knockout mutation of rpoN. Regulation of the glyoxylate pathway by RpoN is likely to be indirect, and represents a unique regulatory role for this sigma factor in bacterial metabolism. INTRODUCTIONBronchopulmonary infections caused by Pseudomonas aeruginosa are the leading cause of mortality for cystic fibrosis (CF) patients. These infections resist eradication by antibiotic therapy and the host immune system, and indicate a need for novel therapeutic strategies. The ability of P. aeruginosa to maintain decade-long infections within the CF lung is attributed in part to virulence mechanisms that evolve as the bacterium adapts to this environment (Lindsey et al., 2008;Nguyen & Singh, 2006). Although P. aeruginosa is nutritionally versatile, within human niches it must adapt to the availability of host-derived nutrients. Within the lungs of CF patients, these nutrients are probably contained in sputum.The composition of CF sputum is complex. It contains host and bacterial cells, as well as various host-and bacterialderived compounds (Hoiby, 1998). Transcriptome studies have indicated that PAO1, a wound isolate of P. aeruginosa, primarily uses amino acids as a carbon source when grown in CF sputum (Palmer et al., 2005;Son et al., 2007). In contrast, a CF isolate of P. aeruginosa uses amino acids and lipids (Palmer et al., 2005;Son et al., 2007). The different carbon utilization patterns by these isolates suggest that P. aeruginosa alters its metabolic pathways during chronic infection of the CF lung. This is supported by the observation that regulatory control of several central metabolic enzymes is altered in FRD1, a CF isolate, compared with PAO1 (Lindsey et al., 2008;Silo-Suh et al., 2005).In a previous study, we exploited t...

Role of Glyoxylate Shunt in Oxidative Stress Response

“…Furthermore, positive regulation by both FruR and integration host factor (IHF) has been reported (42,43). The indirect regulation of aceA by RpoN has been documented in P. aeruginosa (44), but other mechanisms for regulation of the glyoxylate shunt have not been well studied. In particular, it remains unclear how ROS regulate this pathway.…”

Deletion of σ 54 ( rpoN ) Alters the Rate of Autolysis and Biofilm Formation in Enterococcus faecalis

“…The role of 54 in regulating numerous biological properties, including those related to virulence, has been well documented for a variety of bacterial species (3,10,21,42,49,51,52,55,58,59). However, its role in E. faecalis has been limited to observations made regarding its contribution to sensitivity to class IIa bacteriocins through the regulation of sugar PTSs (9,13,22).…”

“…Sigma 54 is required for biofilm formation by Burkholderia cenocepacia as well as its survival within macrophages (51). In the major food-borne pathogen Listeria monocytogenes, 54 is essential for its osmotolerance potential (41) and is responsible for mesentericin sensitivity (14,41), whereas in Pseudomonas aeruginosa, 54 influences the activity of isocitrate lyase (21), alginate biosynthesis (6), and pilin and flagellin production, in addition to several other virulence determinants (44). Sigma 54 also regulates biofilm formation, enterocyte effacement, acid tolerance, flagellar biosynthesis, and several other processes in Escherichia coli (3,49,60).…”

<b><i>Pseudomonas aeruginosa</i></b> and <b><i>Klebsiella</i></b> <b><i>pneumoniae</i></b> Adaptation to Innate Immune Clearance Mechanisms in the Lung

“…Augmented expression of Entner-Doudoroff ( zwf ) and glyoxylate shunt ( aceA and glcB ) regulatory genes in mucoid CF-related P. aeruginosa has been reported [54-56], which conferred advantages for sputum-mediated clearance. Of interest, zwf , aceA , and glcB were constitutively upregulated in mucoid CF isolates, suggesting that adaptation in late-stage CF may include the rewiring of the regulatory networks that control preferential use of metabolites.…”