title: Pseudomonas putida mt-2 tolerates reactive oxygen species generated during matric stress by inducing a major oxidative defense response.
abstract: BACKGROUND
  Soil bacteria typically thrive in water-limited habitats that cause an inherent matric stress to the cognate cells. Matric stress gives rise to accumulation of intracellular reactive oxygen species (ROS), which in turn may induce oxidative stress, and even promote mutagenesis. However, little is known about the impact of ROS induced by water limitation on bacteria performing important processes as pollutant biodegradation in the environment. We have rigorously examined the physiological consequences of the rise of intracellular ROS caused by matric stress for the toluene- and xylene-degrading soil bacterium Pseudomonas putida mt-2.
  
  
  METHODS
  For the current experiments, controlled matric potential stress was delivered to P. putida cells by addition of polyethylene glycol to liquid cultures, and ROS formation in individual cells monitored by a specific dye. The physiological response to ROS was then quantified by both RT-qPCR of RNA transcripts from genes accredited as proxies of oxidative stress and the SOS response along with cognate transcriptional GFP fusions to the promoters of the same genes.
  
  
  RESULTS
  Extensive matric stress at -1.5 MPa clearly increased intracellular accumulation of ROS. The expression of the two major oxidative defense genes katA and ahpC, as well as the hydroperoxide resistance gene osmC, was induced under matric stress. Different induction profiles of the reporters were related to the severity of the stress. To determine if matric stress lead to induction of the SOS-response, we constructed a DNA damage-inducible bioreporter based on the LexA-controlled phage promoter PPP3901. According to bioreporter analysis, this gene was expressed during extensive matric stress. Despite this DNA-damage mediated gene induction, we observed no increase in the mutation frequency as monitored by emergence of rifampicin-resistant colonies.
  
  
  CONCLUSIONS
  Under conditions of extensive matric stress, we observed a direct link between matric stress, ROS formation, induction of ROS-detoxifying functions and (partial) activation of the SOS system. However, such a stress-response regime did not translate into a general DNA mutagenesis status. Taken together, the data suggest that P. putida mt-2 can cope with this archetypal environmental stress while preserving genome stability, a quality that strengthens the status of this bacterium for biotechnological purposes.
authors.affiliation: Department of Plant and Environmental Sciences, Section of Genetics and Microbiology, University of Copenhagen, Thorvaldsensvej 40, 1871, Frederiksberg C, Denmark. nbsv@plen.ku.dk.
authors.forename: Nanna B
authors.initials: NB
authors.lastname: Svenningsen
authors.affiliation: Systems and Synthetic Biology Program, Centro Nacional de Biotecnología (CNB-CSIC), C/ Darwin 3, 28049, Madrid, Spain. drperez@cnb.csic.es.
authors.forename: Danilo
authors.initials: D
authors.lastname: Pérez-Pantoja
authors.affiliation: Systems and Synthetic Biology Program, Centro Nacional de Biotecnología (CNB-CSIC), C/ Darwin 3, 28049, Madrid, Spain. pablo.nikel@cnb.csic.es.
authors.forename: Pablo I
authors.initials: PI
authors.lastname: Nikel
authors.affiliation: Department of Plant and Environmental Sciences, Section of Genetics and Microbiology, University of Copenhagen, Thorvaldsensvej 40, 1871, Frederiksberg C, Denmark. meni@plen.ku.dk.
authors.forename: Mette H
authors.initials: MH
authors.lastname: Nicolaisen
authors.affiliation: Systems and Synthetic Biology Program, Centro Nacional de Biotecnología (CNB-CSIC), C/ Darwin 3, 28049, Madrid, Spain. vdlorenzo@cnb.csic.es.
authors.forename: Víctor
authors.initials: V
authors.lastname: de Lorenzo
authors.affiliation: Department of Plant and Environmental Sciences, Section of Genetics and Microbiology, University of Copenhagen, Thorvaldsensvej 40, 1871, Frederiksberg C, Denmark. oln@plen.ku.dk.
authors.forename: Ole
authors.initials: O
authors.lastname: Nybroe
mesh_terms: D003890:Desiccation; D020869:Gene Expression Profiling; D018384:Oxidative Stress; D016958:Pseudomonas putida / Q000187:drug effects / Q000378:metabolism*; D017382:Reactive Oxygen Species / Q000378:metabolism*; D060888:Real-Time Polymerase Chain Reaction; D013014:SOS Response, Genetics; D012988:Soil Microbiology; D012989:Soil Pollutants / Q000378:metabolism*; D013312:Stress, Physiological; D014050:Toluene / Q000378:metabolism; D014992:Xylenes / Q000378:metabolism
chemical_list: D017382:Reactive Oxygen Species; D012989:Soil Pollutants; D014992:Xylenes; D014050:Toluene