title: Genome reduction boosts heterologous gene expression in Pseudomonas putida.
abstract: BACKGROUND
  The implementation of novel platform organisms to be used as microbial cell factories in industrial applications is currently the subject of intense research. Ongoing efforts include the adoption of Pseudomonas putida KT2440 variants with a reduced genome as the functional chassis for biotechnological purposes. In these strains, dispensable functions removed include flagellar motility (1.1% of the genome) and a number of open reading frames expected to improve genotypic and phenotypic stability of the cells upon deletion (3.2% of the genome).
  
  
  RESULTS
  In this study, two previously constructed multiple-deletion P. putida strains were systematically evaluated as microbial cell factories for heterologous protein production and compared to the parental bacterium (strain KT2440) with regards to several industrially-relevant physiological traits. Energetic parameters were quantified at different controlled growth rates in continuous cultivations and both strains had a higher adenosine triphosphate content, increased adenylate energy charges, and diminished maintenance demands than the wild-type strain. Under all the conditions tested the mutants also grew faster, had enhanced biomass yields and showed higher viability, and displayed increased plasmid stability than the parental strain. In addition to small-scale shaken-flask cultivations, the performance of the genome-streamlined strains was evaluated in larger scale bioreactor batch cultivations taking a step towards industrial growth conditions. When the production of the green fluorescent protein (used as a model heterologous protein) was assessed in these cultures, the mutants reached a recombinant protein yield with respect to biomass up to 40% higher than that of P. putida KT2440.
  
  
  CONCLUSIONS
  The two streamlined-genome derivatives of P. putida KT2440 outcompeted the parental strain in every industrially-relevant trait assessed, particularly under the working conditions of a bioreactor. Our results demonstrate that these genome-streamlined bacteria are not only robust microbial cell factories on their own, but also a promising foundation for further biotechnological applications.
authors.affiliation: Institute of Biochemical Engineering, University of Stuttgart, Allmandring 31, 70569, Stuttgart, Germany. lieder@ibvt.uni-stuttgart.de.
authors.forename: Sarah
authors.initials: S
authors.lastname: Lieder
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: 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: Institute of Biochemical Engineering, University of Stuttgart, Allmandring 31, 70569, Stuttgart, Germany. takors@ibvt.uni-stuttgart.de.
authors.forename: Ralf
authors.initials: R
authors.lastname: Takors
mesh_terms: D061249:Batch Cell Culture Techniques; D018533:Biomass; D004734:Energy Metabolism; D015964:Gene Expression Regulation, Bacterial / Q000235:genetics*; D016680:Genome, Bacterial; D049452:Green Fluorescent Proteins / Q000235:genetics / Q000378:metabolism; D007700:Kinetics; D060847:Metabolic Engineering; D010957:Plasmids / Q000235:genetics / Q000378:metabolism; D016958:Pseudomonas putida / Q000235:genetics* / Q000254:growth & development / Q000378:metabolism
chemical_list: D049452:Green Fluorescent Proteins