Transcriptional Tradeoff between Metabolic and Stress-response Programs in Pseudomonas putida KT2440 Cells Exposed to Toluene

Abstract

When Pseudomonas putida KT2440 cells encounter toluene in the growth medium, they perceive it simultaneously as a potential nutrient to be metabolized, as a membrane-damaging toxic drug to be extruded, and as a macromolecule-disrupting agent from which to protect proteins. Each of these inputs requires a dedicated transcriptional response that involves a large number of genes. We used DNA array technology to decipher the interplay between these responses in P. putida KT2440 subjected to a short challenge (15 min) with toluene. We then compared the results with those in cells exposed to o-xylene (a non-biodegradable toluene counterpart) and 3-methylbenzoate (a specific substrate of the lower TOL pathway of the P. putida pWW0 plasmid). The resulting expression profiles suggest that the bulk of the available transcriptional machinery is reassigned to endure general stress, whereas only a small share of the available machinery is redirected to the degradation of the aromatic compounds. Specifically, both toluene and o-xylene induce the TOL pathways and a dedicated but not always productive metabolic program. Similarly, 3-methylbenzoate induces the expression not only of the lower meta pathway but also of the non-productive and potentially deleterious genes for the metabolism of (nonsubstituted) benzoate. In addition, toluene (and to a lesser extent o-xylene) inhibit motility functions as an unequivocal response to aromatic toxicity. We argue that toluene is sensed by P. putida KT2440 as a stressor rather than as a nutrient and that the inhibition by the aromatic compounds of many functions we tested is the tradeoff for activating stress tolerance genes at a minimal cost in terms of energy.

TrgI, toluene repressed gene I, a novel gene involved in toluene-tolerance in Pseudomonas putida S12

“…The gene coding for the flagellar hook-length protein was downregulated. A relationship between flagella and solvent tolerance has been reported previously in solvent-tolerant P. putida strains Segura et al 2001;Dominguez-Cuevas et al 2006). In each case, different flagella genes were found to influence solvent tolerance.…”

“…Only overexpression of MarA led to increased solvent tolerance, which confirmed earlier observations that this gene is involved in solvent tolerance. Dominguez-Cuevas et al (2006) assessed the transcriptional response of P. putida KT2440[pWW0] to a shock treatment with toluene, o-xylene and 3-methylbenzoate in batch cultures. They concluded that this toluene-degrading strain responds to toluene as a stressor rather than a nutrient.…”

Genome‐wide identification of tolerance mechanisms toward p‐coumaric acid in Pseudomonas putida

“…Some of the changes that can occur in the membrane, when bacteria are exposed to hydrophobic solvents, include vesicle formation, alteration of phospholipid composition, and reduced permeability of the cell membrane (Heipieper & De Bont, 1994; Nicolaou, Gaida, & Papoutsakis, 2010; Ramos et al, 2002). The mechanisms behind tolerance in the model strain P. putida KT2440 has also been studied for different compounds (Benndorf, Thiersch, Loffhagen, Kunath, & Harms, 2006; Domínguez‐Cuevas, González‐Pastor, Marqués, Ramos, & de Lorenzo, 2006; Fernandez, Conde et al, 2012; Fernandez, Niqui‐Arroyo, Conde, Ramos, & Duque, 2012; Roca, Rodríguez‐Herva, Duque, & Ramos, 2008; Santos, Benndorf, & Sá‐Correia, 2004). …”

Pumping iron to keep fit: modulation of siderophore secretion helps efficient aromatic utilization in Pseudomonas putida KT2440

“…Among Pseudomonas, Pseudomonas putida has been extensively studied for its aromatic degradation capability, which has made it a model organism in studies relating to aromatic degradation by microbes (Ramos et al, 1997). The toluene degradation pathway (TOL pathway) in P. putida is one of the most studied pathways in terms of transcriptional regulation and expression (Domínguez-Cuevas et al, 2006;Ramos et al, 1997;Silva-Rocha et al, 2011). In spite of significant information being available on the genomic determinants of aromatic degradation by P. putida, there is limited information on the phenotypic attributes influencing its aromatic utilization capability.…”