Abstract
Growing environmental concern sparks renewed interest in the sustainable production of (bio)materials that can replace oil-derived goods. Polyhydroxyalkanoates (PHAs) are isotactic polymers that play a critical role in the central metabolism of producer bacteria, as they act as dynamic reservoirs of carbon and reducing equivalents. PHAs continue to attract industrial attention as a starting point toward renewable, biodegradable, biocompatible, and versatile thermoplastic and elastomeric materials. Pseudomonas species have been known for long as efficient biopolymer producers, especially for medium-chain-length PHAs. The surge of synthetic biology and metabolic engineering approaches in recent years offers the possibility of exploiting the untapped potential of Pseudomonas cell factories for the production of tailored PHAs. In this article, an overview of the metabolic and regulatory circuits that rule PHA accumulation in Pseudomonas putida is provided, and approaches leading to the biosynthesis of novel polymers (e.g., PHAs including nonbiological chemical elements in their structures) are discussed. The potential of novel PHAs to disrupt existing and future market segments is closer to realization than ever before. The review is concluded by pinpointing challenges that currently hinder the wide adoption of bio-based PHAs, and strategies toward programmable polymer biosynthesis from alternative substrates in engineered P. putida strains are proposed.
Highlights
Growing global environmental concerns urgently call for smart alternatives to the use of oil-derived commodities to reduce our dependency on limited fossil resources— while limiting pollution and CO emissions
We focus on the biochemical mechanisms that remain unexplored targets for manipulation and on the interplay of factors that drives biopolymer production
The physical properties of these polymers were not analyzed in this work, the results indicate that biosynthesis of PHAs bearing methylphenoxy substituents from methylphenoxyoctanoates are highly dependent upon the methyl substituent position.[ ]
Summary
Growing global environmental concerns urgently call for smart alternatives to the use of oil-derived commodities to reduce our dependency on limited fossil resources— while limiting pollution and CO emissions. Even though the e ector of PhaD is still unknown, a CoA intermediate of fatty acid metabolism (i.e., -oxidation) or the TCA cycle has been proposed to be involved in this regulatory loop.[ , ] the PhaF phasin has been proposed to modulate the expression of the pha genes and to exert an e ect on the whole transcriptome—probably due to its DNA binding and histone-like properties, since this protein associates to the nucleoid.[ ] it is still unclear whether or not PhaF binds the promoter region of pha genes, deleting phaF in P. putida KT leads to a significant decrease of phaC and phaI transcript levels, resulting in a reduction of PHA accumulation.[ b] PhaF is a multifunctional phasin that plays a role in granule segregation during cell division and as a transcriptional regulator.[ b] Very recently, a direct interaction of PhaF and PhaD has been demonstrated— suggesting the existence of a multicomplex regulatory system formed by PHA granules, a PhaD–PhaF complex, and the target DNA.[ ]. Despite that this new material has only – % (mol/mol) nitrophenoxy units, the physical appearance (yellow and elastic) was di erent from that of the polymer obtained from nonanoic acid (whitish and sticky).[ ]
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