Comparison of mcl-Poly(3-hydroxyalkanoates) synthesis by different Pseudomonas putida strains from crude glycerol: citrate accumulates at high titer under PHA-producing conditions.

Ignacio Poblete-Castro,Rene Oehlert,Manfred Rohde,Danielle Binger

doi:10.1186/s12896-014-0110-z

Ignacio Poblete-Castro, Rene Oehlert + Show 2 more

Open Access

https://doi.org/10.1186/s12896-014-0110-z

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Abstract

BackgroundAchieving 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.ResultsAmong 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.ConclusionsOverall, 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.

Highlights

Achieving a sustainable society requires, among other things, the use of renewable feedstocks to replace chemicals obtained from petroleum-derived compounds
Given the high metabolic versatility shown by some Pseudomonas putida strains [23], waste materials from different streams have been used as carbon substrate to produce medium-chain-length poly(3-hydroxyalkanoates) (mcl-PHA)
Raw glycerol is produced as a byproduct of the chemical conversion of fatty acids into biodiesel, a process that results in the following basic products: glycerol (60-80%), water (10%), organic matter (8%), ash (8%), and methanol (0.5-20%)

Summary

Introduction

Achieving a sustainable society requires, among other things, the use of renewable feedstocks to replace chemicals obtained from petroleum-derived compounds. Production of PHAs using waste materials from agriculture residues and waste water treatment streams as a carbon substrate has shown to be a very promising alternative [6,7,8], since raw materials account for the majority of production costs in the bacterial synthesis of PHAs [4,9] These processes have mainly focused on the synthesis of Poly(3-hydroxybutyrate) (PHB), the first and best-characterized PHA [1]. Given the high metabolic versatility shown by some Pseudomonas putida strains [23], waste materials from different streams have been used as carbon substrate to produce mcl-PHAs. Efficient synthesis of mcl-PHAs was obtained from animal wastes [24], PET [25] and raw glycerol [26]. An exo-metabolome analysis was performed to identify and quantify byproduct formation during the fermentation process in bioreactors, and the causes for the low yield of biomass and biopolymers in Pseudomonas putida fed with glycerol were elucidated

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