title: Comparison of mcl-Poly(3-hydroxyalkanoates) synthesis by different Pseudomonas putida strains from crude glycerol: citrate accumulates at high titer under PHA-producing conditions.
abstract: BACKGROUND
  Achieving a sustainable society requires, among other things, the use of renewable feedstocks to replace chemicals obtained from petroleum-derived compounds. Crude glycerol synthesized inexpensively as a byproduct of biodiesel production is currently considered a waste product, which can potentially be converted into value-added compounds by bacterial fermentation. This study aimed at evaluating several characterized P. putida strains to produce medium-chain-length poly(3-hydroxyalkanoates) (mcl-PHA) using raw glycerol as the only carbon/energy source.
  
  
  RESULTS
  Among all tested strains, P. putida KT2440 most efficiently synthesized mcl-PHA under nitrogen-limiting conditions, amassing more than 34% of its cell dry weight as PHA. Disruption of the PHA depolymerase gene (phaZ) in P. putida KT2440 enhanced the biopolymer titer up to 47% PHA (%wt/wt). The low biomass and PHA titer found in the mutant strain and the wild-type strain KT2440 seems to be triggered by the high production of the side-product citrate during the fermentation process which shows a high yield of 0.6 g/g.
  
  
  CONCLUSIONS
  Overall, this work demonstrates the importance of choosing an appropriate microbe for the synthesis of mcl-PHA from waste materials, and a close inspection of the cell metabolism in order to identify undesired compounds that diminish the availability of precursors in the synthesis of biopolymers such as polyhydroxyalkanoates. Future metabolic engineering works should focus on reducing the production of citrate in order to modulate resource allocation in the cell's metabolism of P. putida, and finally increase the biopolymer production.
authors.affiliation: Facultad de Ciencias Biológicas, Center for Bioinformatic and Integrative Biology, Biosystems Engineering Laboratory, Universidad Andrés Bello, Santiago, 8340176, Chile. ignacio.poblete@unab.cl.|Helmholtz Centre for Infection Biology, Microbial Drugs Group, Braunschweig, D-38124, Germany. ignacio.poblete@unab.cl.
authors.forename: Ignacio
authors.initials: I
authors.lastname: Poblete-Castro
authors.affiliation: Helmholtz Centre for Infection Biology, Systems and Synthetic Biology, Braunschweig, D-38124, Germany. danielle.janus@rub.de.
authors.forename: Danielle
authors.initials: D
authors.lastname: Binger
authors.affiliation: Helmholtz Centre for Infection Biology, Microbial Drugs Group, Braunschweig, D-38124, Germany. rene.oehlert@haw-hamburg.de.
authors.forename: Rene
authors.initials: R
authors.lastname: Oehlert
authors.affiliation: Helmholtz Centre for Infection Biology, Molecular Mechanism of Streptococci Group, Braunschweig, D-38124, Germany. manfred.rohde@helmholtz-hzi.de.
authors.forename: Manfred
authors.initials: M
authors.lastname: Rohde
mesh_terms: D002951:Citrates / Q000378:metabolism*; D005285:Fermentation; D005990:Glycerol / Q000378:metabolism*; D054813:Polyhydroxyalkanoates / Q000737:chemistry / Q000378:metabolism*; D016958:Pseudomonas putida / Q000737:chemistry / Q000145:classification / Q000235:genetics / Q000378:metabolism*
chemical_list: D002951:Citrates; D054813:Polyhydroxyalkanoates; D005990:Glycerol