title: Anoxic metabolism and biochemical production in Pseudomonas putida F1 driven by a bioelectrochemical system.
abstract: BACKGROUND
  Pseudomonas putida is a promising host for the bioproduction of chemicals, but its industrial applications are significantly limited by its obligate aerobic character. The aim of this paper is to empower the anoxic metabolism of wild-type Pseudomonas putida to enable bioproduction anaerobically, with the redox power from a bioelectrochemical system (BES).
  
  
  RESULTS
  The obligate aerobe Pseudomonas putida F1 was able to survive and produce almost exclusively 2-Keto-gluconate from glucose under anoxic conditions due to redox balancing with electron mediators in a BES. 2-Keto-gluconate, a precursor for industrial anti-oxidant production, was produced at an overall carbon yield of over 90 % based on glucose. Seven different mediator compounds were tested, and only those with redox potential above 0.207 V (vs standard hydrogen electrode) showed interaction with the cells. The productivity increased with the increasing redox potential of the mediator, indicating this was a key factor affecting the anoxic production process. P. putida cells survived under anaerobic conditions, and limited biofilm formation could be observed on the anode's surface. Analysis of the intracellular pools of ATP, ADP and AMP showed that cells had an increased adenylate energy charge suggesting that cells were able to generate energy using the anode as terminal electron acceptor. The analysis of NAD(H) and NADP(H) showed that in the presence of specific extracellular electron acceptors, the NADP(H) pool was more oxidised, while the NAD(H) pool was unchanged. This implies a growth limitation under anaerobic conditions due to a shortage of NADPH and provides a way to limit biomass formation, while allowing cell maintenance and catalysis at high purity and yield.
  
  
  CONCLUSIONS
  For the first time, this study proved the principle that a BES-driven bioconversion of glucose can be achieved for a wild-type obligate aerobe. This non-growth bioconversion was in high yields, high purity and also could deliver the necessary metabolic energy for cell maintenance. By combining this approach with metabolic engineering strategies, this could prove to be a powerful new way to produce bio-chemicals and fuels from renewables in both high yield and high purity.
authors.affiliation: Centre for Microbial Electrochemical Systems (CEMES), The University of Queensland, Office 618, Gehrmann Building (60), St. Lucia, Brisbane, QLD 4072 Australia ; Advanced Water Management Centre (AWMC), The University of Queensland, Brisbane, Australia.
authors.forename: Bin
authors.initials: B
authors.lastname: Lai
authors.affiliation: Centre for Microbial Electrochemical Systems (CEMES), The University of Queensland, Office 618, Gehrmann Building (60), St. Lucia, Brisbane, QLD 4072 Australia ; Advanced Water Management Centre (AWMC), The University of Queensland, Brisbane, Australia.
authors.forename: Shiqin
authors.initials: S
authors.lastname: Yu
authors.affiliation: School of Chemistry and Molecular Biosciences, The University of Queensland, Brisbane, Australia.
authors.forename: Paul V
authors.initials: PV
authors.lastname: Bernhardt
authors.affiliation: Laboratory of Microbial Ecology and Technology (LabMET), Ghent University, Ghent, Belgium.
authors.forename: Korneel
authors.initials: K
authors.lastname: Rabaey
authors.affiliation: Centre for Microbial Electrochemical Systems (CEMES), The University of Queensland, Office 618, Gehrmann Building (60), St. Lucia, Brisbane, QLD 4072 Australia ; Advanced Water Management Centre (AWMC), The University of Queensland, Brisbane, Australia.
authors.forename: Bernardino
authors.initials: B
authors.lastname: Virdis
authors.affiliation: Centre for Microbial Electrochemical Systems (CEMES), The University of Queensland, Office 618, Gehrmann Building (60), St. Lucia, Brisbane, QLD 4072 Australia ; Advanced Water Management Centre (AWMC), The University of Queensland, Brisbane, Australia.
authors.forename: Jens O
authors.identifier: 0000-0001-5006-0819
authors.initials: JO
authors.lastname: Krömer
keywords: Anoxic metabolism; Bio-production; Bioelectrochemical system; Chemical feedstocks; Extracellular electron transfer; Pseudomonas putida F1; Redox mediators