Cultivation temperature modulated the monomer composition and polymer properties of polyhydroxyalkanoate synthesized by Cupriavidus sp. L7L from levulinate as sole carbon source

Enhancing polyhydroxyalkanoate production in Cupriavidus sp. L7L through wcaJ gene deletion

Cupriavidus sp. L7L synthesizes a high content of ductile polyhydroxyalkanoate. However, during fermentation, the medium's viscosity gradually increases, eventually reaching a level similar to 93 % glycerol, leading to fermentation termination and difficulties in cell harvest. A non-mucoid variant was isolated from a mini-Tn5 mutant library with the transposon inserted at the promoter sequence upstream of the wcaJ gene. Deletion of wcaJ eliminated the mucoid-colony appearance. The complementation experiment confirmed the association between wcaJ gene expression and mucoid-colony formation. Additionally, the wild-type strain exhibited a faster specific growth rate than the deletion strain using levulinate (Lev) as a carbon source. In fed-batch fermentation, Cupriavidus sp. L7L∆wcaJ showed similar PHA content and monomer composition to the wild-type strain. However, the extended fermentation time resulted in a 42 % increase in PHA concentration. After fed-batch fermentation, the deletion strain's medium had only 8.75 % of the wild-type strain's extracellular polymeric substance content. Moreover, the deletion strain's medium had a much lower viscosity (1.04 mPa·s) than the wild-type strain (194.7 mPa·s), making bacterial cell collection easier through centrifugation. In summary, Cupriavidus sp. L7L∆wcaJ effectively addressed difficulties in cell harvest, increased PHA production, and Lev-to-PHA conversion efficiency, making these characteristics advantageous for industrial-scale PHA production.

Biodegradable Polyhydroxyalkanoates with a Different Set of Valerate Monomers: Chemical Structure and Physicochemical Properties

The properties, features of thermal behavior and crystallization of copolymers containing various types of valerate monomers were studied depending on the set and ratio of monomers. We synthesized and studied the properties of three-component copolymers containing unusual monomers 4-hydroxyvalerate (4HV) and 3-hydroxy-4-methylvalerate (3H4MV), in addition to the usual 3-hydroxybutyrate (3HB) and 3-hydroxyvalerate (3HV) monomers. The results showed that P(3HB-co-3HV-co-4HV) and P(3HB-co-3HV-co-3H4MV) terpolymers tended to increase thermal stability, especially for methylated samples, including an increase in the gap between melting point (Tmelt) and thermal degradation temperature (Tdegr), an increase in the melting point and glass transition temperature, as well as a lower degree of crystallinity (40-46%) compared with P(3HB-co-3HV) (58-66%). The copolymer crystallization kinetics depended on the set and ratio of monomers. For terpolymers during exothermic crystallization, higher rates of spherulite formation (Gmax) were registered, reaching, depending on the ratio of monomers, 1.6-2.0 µm/min, which was several times higher than the Gmax index (0.52 µm/min) for the P(3HB-co-3HV) copolymer. The revealed differences in the thermal properties and crystallization kinetics of terpolymers indicate that they are promising polymers for processing into high quality products from melts.

Microbial community structure and potential function associated with poly-3-hydroxybutyrate biopolymer-boosted activation of peroxymonosulfate for waste-activated sludge decontamination

Excess waste-activated sludge (WAS) is a major biosolid management problem due to its biohazardous and recalcitrant content of phthalate esters (PAEs). This study aimed to assess the combined use of biopolymer, poly-3-hydroxybutyrate and peroxymonosulfate to degrade PAEs and decontaminate WAS. Poly-3-hydroxybutyrate was biosynthesized by Cupriavidus sp. L7L. The combined poly-3-hydroxybutyrate and peroxymonosulfate process removed 86 % of PAEs from WAS in 12 h. The carbonyl groups of poly-3-hydroxybutyrate were conducive to peroxymonosulfate activation leading to PAE degradation followed the radical pathway and surface-mediated electron transfer. Poly-3-hydroxybutyrate and peroxymonosulfate also enriched the PAE-biodegrading microbes in WAS. The microbial population and the functional composition in response to peroxymonosultate treatment was identified, with the genus Sulfurisoma being the most abundant. This synergistic treatment, i.e., advanced oxidation process, was augmented by highly promising microbial polyesters, exhibited important implications for WAS pretreatment toward circular bioeconomy that encompasses carbon-neutral biorefinery and mitigate pollution.

Production of polyhydroxyalkanoates containing monomers conferring amorphous and elastomeric properties from renewable resources: Current status and future perspectives

Petrochemical-based plastics cause environmental pollution and threaten humans and ecosystems. Polyhydroxyalkanoate (PHA) is considered a promising alternative to nondegradable plastics since it is eco-friendly and biodegradable polymer having similar properties to conventional plastics. PHA's material properties are generally determined by composition and type of monomers in PHA. PHA can be designed in tailor-made manner for their suitable application areas. Among many monomers in PHAs, ω-hydroxalkanoates such as 3-hydroxypropionate (3HP), 4-hydroxybutyrate (4HB), 5-hydroxyvalerate (5HV), and 6-hydroxyhexanoate (6HHx) and medium-chain-length 3-hydroxyalkanoate such as 3-hydroxyhexanoate (3HHx) and 4-hydroxyvalerate (4HV), have been examined as potential monomers able to confer amorphous and elastomer properties when these are incorporated as comonomer in poly(3-hydroxybutyrate) copolymer that has 3HB as main monomer along with comonomers in different monomer fraction. Herein, recent advances in production of PHAs designed to have amorphous and elastomeric properties from renewable sources such as lignocellulose, levulinic acid, crude glycerol, and waste oil are discussed.

Biosynthesis and Properties of a P(3HB-co-3HV-co-4HV) Produced by Cupriavidus necator B-10646

Synthesis of P(3HB-co-3HV-co-4HV) copolymers by the wild-type strain Cupriavidus necator B-10646 on fructose or sodium butyrate as the main C-substrate with the addition of γ-valerolactone as a precursor of 3HV and 4HV monomers was studied. Bacterial cells were cultivated in the modes that enabled production of a series of copolymers with molar fractions of 3HV (from 7.3 to 23.4 mol.%) and 4HV (from 1.9 to 4.7 mol.%) with bacterial biomass concentration (8.2 ± 0.2 g/L) and PHA content (80 ± 2%). Using HPLC, DTA, DSC, X-Ray, SEM, and AFM, the physicochemical properties of copolymers and films prepared from them have been investigated as dependent on proportions of monomers. Copolymers are characterized by a reduced degree of crystallinity (C_x 38-49%) molecular weight characteristics M_n (45-87 kDa), and M_w (201-248 kDa) compared with P(3HB). The properties of the films surface of various composition including the porosity and surface roughness were studied. Most of the samples showed a decrease in the average pore area and an increase in their number with a total increase in 3HV and 4HV monomers. The results allow scaling up the productive synthesis of P(3HB-co-3HV-co-4HV) copolymers using Cupriavidus necator B-10646.

Metal-free catalysis for organic micropollutant degradation in waste activated sludge via poly(3-hydroxybutyrate) biopolymers using Cupriavidus sp. L7L coupled with peroxymonosulfate

This study employed a novel and environment-friendly biopolymer/oxidant catalytic system, viz., poly(3-hydroxybutyrate)/peroxymonosulfate (PHB/PMS), for pretreating wastewater sludge for the first time. Under optimal conditions, i.e., 3.1 × 10^-4 M of PMS and 3.3 g/L of PHB at pH = 6.0, the PAHs in the sludge matrix was decreased by 79 % in 12 h. Increase in salinity (75 % synthetic seawater) achieved 83 % of PAHs degradation. Functional groups (CO) of the biopolymer matrix were active centers for biopolymer-mediated electron transfer that produced reactive oxygen species (SO₄^-, HO, and ¹O₂) for adsorption and catalytic oxidation of PAHs in the sludge. Functional metagenomic analysis revealed the main genus, Conexibacter (phylum, Actinobacteria) exhibited PAH-degrading function with high efficiency in the biodegradation of PAHs from sludge pretreated with PHB/PMS. Coupling chemical oxidation and biostimulation using bacterial polymer-based biomaterials is effective and beneficial for pretreating wastewater sludge toward circular bioeconomy.

Metabolic Engineering of Escherichia coli for Production of Polyhydroxyalkanoates with Hydroxyvaleric Acid Derived from Levulinic Acid

Polyhydroxyalkanoates (PHAs) are emerging as alternatives to plastics by replacing fossil fuels with renewable raw substrates. Herein, we present the construction of engineered Escherichia coli strains to produce short-chain-length PHAs (scl-PHAs), including the monomers 4-hydroxyvalerate (4HV) and 3-hydroxyvalerate (3HV) produced from levulinic acid (LA). First, an E. coli strain expressing genes (lvaEDABC) from the LA metabolic pathway of Pseudomonas putida KT2440 was constructed to generate 4HV-CoA and 3HV-CoA. Second, both PhaAB enzymes from Cupriavidus necator H16 were expressed to supply 3-hydroxybutyrate (3HB)-CoA from acetyl-CoA. Finally, PHA synthase (PhaC_Cv) from Chromobacterium violaceum was introduced for the subsequent polymerization of these three monomers. The resulting E. coli strains produced four PHAs (w/w% of dry cell weight): 9.1 wt% P(4HV), 1.7 wt% P(3HV-co-4HV), 24.2 wt% P(3HB-co-4HV), and 35.6 wt% P(3HB-co-3HV-co-4HV).

Regulated strategies of cold-adapted microorganisms in response to cold: a review

There are a large number of active cold-adapted microorganisms in the perennial cold environment. Due to their high-efficiency and energy-saving catalytic properties, cold-adapted microorganisms have become valuable natural resources with potential in various biological fields. In this study, a series of cold response strategies for microorganisms were summarized. This mainly involves the regulation of cell membrane fluidity, synthesis of cold adaptation proteins, regulators and metabolic changes, energy supply, and reactive oxygen species. Also, the potential of biocatalysts produced by cold-adapted microorganisms including cold-active enzymes, ice-binding proteins, polyhydroxyalkanoates, and surfactants was introduced, which provided a guidance for expanding its application values. Overall, new insights were obtained on response strategies of microorganisms to cold environments in this review. This will deepen the understanding of the cold tolerance mechanism of cold-adapted microorganisms, thus promoting the establishment and application of low-temperature biotechnology.

In vivo and Post-synthesis Strategies to Enhance the Properties of PHB-Based Materials: A Review

The transition toward "green" alternatives to petroleum-based plastics is driven by the need for "drop-in" replacement materials able to combine characteristics of existing plastics with biodegradability and renewability features. Promising alternatives are the polyhydroxyalkanoates (PHAs), microbial biodegradable polyesters produced by a wide range of microorganisms as carbon, energy, and redox storage material, displaying properties very close to fossil-fuel-derived polyolefins. Among PHAs, polyhydroxybutyrate (PHB) is by far the most well-studied polymer. PHB is a thermoplastic polyester, with very narrow processability window, due to very low resistance to thermal degradation. Since the melting temperature of PHB is around 170-180°C, the processing temperature should be at least 180-190°C. The thermal degradation of PHB at these temperatures proceeds very quickly, causing a rapid decrease in its molecular weight. Moreover, due to its high crystallinity, PHB is stiff and brittle resulting in very poor mechanical properties with low extension at break, which limits its range of application. A further limit to the effective exploitation of these polymers is related to their production costs, which is mostly affected by the costs of the starting feedstocks. Since the first identification of PHB, researchers have faced these issues, and several strategies to improve the processability and reduce brittleness of this polymer have been developed. These approaches range from the in vivo synthesis of PHA copolymers, to the enhancement of post-synthesis PHB-based material performances, thus the addition of additives and plasticizers, acting on the crystallization process as well as on polymer glass transition temperature. In addition, reactive polymer blending with other bio-based polymers represents a versatile approach to modulate polymer properties while preserving its biodegradability. This review examines the state of the art of PHA processing, shedding light on the green and cost-effective tailored strategies aimed at modulating and optimizing polymer performances. Pioneering examples in this field will be examined, and prospects and challenges for their exploitation will be presented. Furthermore, since the establishment of a PHA-based industry passes through the designing of cost-competitive production processes, this review will inspect reported examples assessing this economic aspect, examining the most recent progresses toward process sustainability.

Metabolic engineering of Pseudomonas putida for the production of various types of short-chain-length polyhydroxyalkanoates from levulinic acid

Poly(3-hydroxybutyrate), a short-chain-length polyhydroxyalkanoate (scl-PHA), is considered as a good alternative to conventional synthetic plastics. However, various biopolymers with diverse characteristics are still in demand. In this study, four different types of scl-PHA were successfully produced by engineering levulinic acid (LA) utilization metabolic pathway and expressing heterologous PHA synthase (PhaEC), acetyl-CoA acetyltransferase (PhaA), and acetyl-CoA reductase (PhaB) in Pseudomonas putida EM42. Poly(3-hydroxybutyrate-co-3-hydroxyvalerate) [P(3HB-co-3HV)], poly(3-hydroxyvalerate-co-4-hydroxyvalerate) [P(3HV-co-4HV)] and poly(3-hydroxybutyrate-co-3-hydroxyvalerate-co-4-hydroxyvalerate) [P(3HB-co-3HV-co-4HV)] were produced by the natural LA pathway, poly(4-hydroxyvalerate) by lvaAB-deleted LA pathway, and P(3HV-co-4HV) and P(3HB-co-3HV-co-4HV) with relatively high 3HV by fadB-deleted LA pathway. PHA with different monomer fractions could be produced using different PHA synthases. Scl-PHA contents reached approximately 40% of cell dry mass under non-optimized flask culture. This demonstrates that the LA catabolic pathway may be a good alternative route to provide monomers for the production of various types of PHA.

Engineering biosynthesis of polyhydroxyalkanoates (PHA) for diversity and cost reduction

PHA, a family of natural biopolymers aiming to replace non-degradable plastics for short-term usages, has been developed to include various structures such as short-chain-length (scl) and medium-chain-length (mcl) monomers as well as their copolymers. However, PHA market has been grown slowly since 1980s due to limited variety with good mechanical properties and the high production cost. Here, we review most updated strategies or approaches including metabolic engineering, synthetic biology and morphology engineering on expanding PHA diversity, reducing production cost and enhancing PHA production. The extremophilic Halomonas spp. are taken as examples to show the feasibility and challenges to develop next generation industrial biotechnology (NGIB) for producing PHA more competitively.