In vivo and in vitro depolymerizations of intracellular medium-chain-length poly-3-hydroxyalkanoates produced by Pseudomonas putida Bet001

Polyhydroxyalkanoates, the bioplastics of microbial origin: Properties, biochemical synthesis, and their applications

The rising plastic pollution deteriorates the environment significantly as these petroleum-based plastics are not biodegradable, and their production requires natural fuels (energy source) and other resources. Polyhydroxyalkanoates (PHAs) are bioplastic and a sustainable and eco-friendly alternative to synthetic plastics. PHAs can be entirely synthesized using various microorganisms such as bacteria, algae, and fungi. These value-added biopolymers show promising properties such as enhanced biodegradability, biocompatibility, and other chemo-mechanical properties. Further, it has been established that the properties of PHA polymers depend on the substrates and chemical composition (monomer unit) of these polymers. PHAs hold great potential as an alternative to petroleum-based polymers, and further research for economic production and utilization of these biopolymers is required. The review describes the synthesis mechanism and different properties of microbially synthesized PHAs for various applications. The classification of PHAs and the multiple techniques necessary for their detection and evaluation have been discussed. In addition, the synthesis mechanism involving the genetic regulation of these biopolymers in various microbial groups has been described. This review provides information on various commercially available PHAs and their application in multiple sectors. The industrial production of these microbially synthesized polymers and the different extraction methods have been reviewed in detail. Furthermore, the review provides an insight into the potential applications of this biopolymer in environmental, industrial, and biomedical applications.

Composite of medium-chain-length polyhydroxyalkanoates-co-methyl acrylate and carbon nanotubes as innovative electrodes modifier in microbial fuel cell

A microbial fuel cell is a sustainable and environmental-friendly device that combines electricity generation and wastewater treatment through metabolic activities of microorganisms. However, low power output from inadequate electron transfer to the anode electrode hampers its practical implementation. Nanocomposites of oxidized carbon nanotubes and medium-chain-length polyhydroxyalkanoates (mcl-PHA) grafted with methyl acrylate monomers enhance the electrochemical function of electrodes in microbial fuel cell. Extensive polymerization of methyl acrylate monomers within mcl-PHA matrix, and homogenous dispersion of carbon nanotubes within the graft matrix are responsible for the enhancement. Modified electrodes exhibit high conductivities, better redox peak and reduction of cell internal resistance up to 76%. A stable voltage output at almost 700 mV running for 225 H generates maximum power and current density of 351 mW/m² and 765 mA/m² , respectively. Superior biofilm growth on modified surface is responsible for improved electron transfer to the anode hence stable and elevated power output generation.

Integrated strain engineering and bioprocessing strategies for high-level bio-based production of 3-hydroxyvalerate in Escherichia coli

As petro-based production generates numerous environmental impacts and their associated technological concerns, bio-based production has been well recognized these days as a modern alternative to manufacture chemical products in a more renewable, environmentally friendly, and sustainable manner. Herein, we report the development of a microbial bioprocess for high-level and potentially economical production of 3-hydroxyvalerate (3-HV), a valuable special chemical with multiple applications in chemical, biopolymer, and pharmaceutical industries, from glycerol, which can be cheaply and renewably refined as a byproduct from biodiesel production. We used our recently derived 3-HV-producing Escherichia coli strains for bioreactor characterization under various culture conditions. In the parental strain, 3-HV biosynthesis was limited by the intracellular availability of propionyl-CoA, whose formation was favored by anaerobic conditions, which often compromised cell growth. With appropriate strain engineering, we demonstrated that 3-HV can be effectively produced under both microaerobic (close to anaerobic) and aerobic conditions, which determine the direction of dissimilated carbon flux toward the succinate node in the tricarboxylic acid (TCA) cycle. We first used the ∆sdhA single mutant strain, in which the dissimilated carbon flux was primarily directed to the Sleeping beauty mutase (Sbm) pathway (via the reductive TCA branch, with enhanced cell growth under microaerobic conditions, achieving 3.08 g L^-1 3-HV in a fed-batch culture. In addition, we used the ∆sdhA-∆iclR double mutant strain, in which the dissimilated carbon flux was directed from the TCA cycle to the Sbm pathway via the deregulated glyoxylate shunt, for cultivation under rather aerobic conditions. In addition to demonstrating effective cell growth, this strain has shown impressive 3-HV biosynthesis (up to 10.6 g L^-1), equivalent to an overall yield of 18.8% based on consumed glycerol, in aerobic fed-batch culture. This study not only represents one of the most effective bio-based production of 3-HV from structurally unrelated carbons to date, but also highlights the importance of integrated strain engineering and bioprocessing strategies to enhance bio-based production.Key points• TCA cycle engineering was applied to enhance 3-HV biosynthesis in E. coli. • Effects of oxygenic conditions on 3-HV in E. coli biosynthesis were investigated. • Bioreactor characterization of 3-HV biosynthesis in E. coli was performed.