Polyhydroxyalkanoates Research Articles

Advancing Sustainability: Utilizing Bacterial Polyhydroxyalkanoate for Food Packaging

Polyhydroxyalkanoates (PHAs) are promising biodegradable polymers known for their biodegradability and eco-friendly properties. Recent studies indicate that PHAs can reduce the environmental impact by up to 50% compared to petroleum-based plastics. This comprehensive review evaluates the application of PHAs in sustainable food packaging, covering over 100 studies published between 2018 and 2023. The review highlights advancements in PHA production, with a focus on submerged and solid-state fermentation methods, achieving up to a 60% improvement in production efficiency through optimized culture selection. Sustainable extraction and purification methods have been identified, reducing energy consumption by 30%. Blending PHAs with other biodegradable polymers like polylactic acid, starch, and cellulose enhances material performance, with up to a 40% improvement in mechanical properties. The incorporation of antimicrobial agents and essential oils has been shown to extend the shelf life by 25% while maintaining food safety standards. This review underscores the potential of active PHA-based packaging in improving the barrier properties by 35% when combined with coatings, positioning PHA as a key material for the future of environmentally responsible and safe food packaging.

Innovative approaches for enhanced nutrient (N and P) removal and biosecurity in marine recirculating aquaculture systems using biofloc and ultrafiltration combined systems

Marine recirculating aquaculture systems (marine RAS) are increasingly utilized for their high productivity and minimal environmental impact. However, effective nutrient management and biosecurity measures remain crucial for sustainable operation of marine RAS. This study successfully established a simultaneous nitrification and denitrification (SND) process using a biofloc technology (BFT)–ultrafiltration (UF) combined approach. A stable autotrophic marine nitrification system was rapidly initiated within 23 days using a ceramic ring (CR)–granular activated carbon (GAC)–UF process (CGUF), followed by the substitution of polyhydroxyalkanoates (PHA) for GAC filter to achieve rapid start-up of SND in 24 h (CG/PUF). Soluble reactive phosphate (SRP) was removed in-situ via biofloc adsorption. The co-existence of ammonia-oxidizing archaea (Candidatus_Nitrosopumilus) and denitrifying bacteria (Stenotrophomonas, Ruegeria and Ilumatobacter) synergistic promoted the SND start-up in CG/PUF process. Stenotrophomonas emerged as the keystone species which closely linked to amoA/B/C, hao and nosZ genes (p < 0.05). The CG/PUF process effectively enhanced the biosecurity of marine RAS, with 100 % elimination of potential pathogens (Vibrio and Tenacibaculum). UF membrane could maintain fluxes at 15 L∙ m−2∙ h−1 (LMH) for 180 days, with a 2-day intermittent hydraulic flushing keeping transmembrane pressure below 50 kPa. These findings provide insights for broader application of BFT–UF combined process in marine RAS.

Influence of synthetic carbon grade on the metabolic flux of polyhydroxyalkanoate monomeric constitution synthesized by Bacillus cereus AAR-1

Carbon substrate is a pivotal factor influencing polyhydroxyalkanoate (PHA) properties of varied industrial importance. Three synthetic sucrose samples with varying manufacturing purity levels were selected as carbon substrates to synthesize diverse PHAs using a wild-type Bacillus cereus AAR-1. Comparative monomeric analyses of the extracted biopolymers revealed Poly (3-hydroxytetradecanoate) (P3HTD), Poly(3-hydroxybutyrate-co-2-hydroxytetradecanoate) [P(3HB-co-2HTD)], and Poly(3-hydroxybutyrate) (P3HB) with carbon elemental contents that ranged from 39 to 53 % and no nitrogen detected. The decomposition temperature of [P(3HB-co-2HTD)] was 279 °C, indicating higher thermal stability than the individual monomeric units. Notably, the homopolymer P3HTD exhibited an increased melting temperature of 172.4 °C and a reduced crystallinity percentage (Xc % = 20.7 %), crucial properties for bioplastics and medical sector applications. All the biopolymers displayed a low specific heat capacity ranging between 0.03 and 0.05 J/g°C, suitable for applications such as thermal storage materials and temperature-regulating textiles. The results suggest that different carbon purity grades influenced homopolymer accumulated in Bacillus cereus AAR-1.

Moderately halophilic bacterium Halomonas alkalicola strain Ext as a platform for poly(3-hydroxybutyrate-co-3-hydroxyvalerate) copolymer production with fruit peels residues as sole carbon source

Polyhydroxyalkanoates (PHAs) are synthesized by a variety of microorganisms as intracellular storage granules under imbalanced nutrition and excess carbon. Carbon sources are key contributors to the high cost of PHA production, hence the need for exploration of cheap and sustainable raw materials for bacteria fermentation. In the present study, Halomonas alkalicola strain Ext isolated from a hypersaline lake in Kenya was assessed for its ability to utilize fruit peels hydrolysates (FPH) as sole carbon sources for PHA production. Sugars were extracted from dried peels of banana, mango, orange, and pineapple fruits through mechanical pretreatment and dilute acid hydrolysis. Fruit peels pretreated with 3 % H2SO4 at 121℃ were utilized for shake flask fermentation to produce PHAs by Halomonas alkalicola Ext. At optimal C:N ratios of between 20:1 and 30:1, the bacterium could produce up to 0.45±0.03, 0.394±0.12, 0.39±0.05, and 0.28±0.0 g/L of PHAs from hydrolysates of orange peels, mango peels, banana peels, and pineapple peels, respectively. A maximum PHA content of 16.92 % was achieved on orange peels hydrolysates with 4 % substrate loading. Monomer analysis with gas chromatography-mass spectrometry (GC-MS) revealed that the bacterium produced a copolymer Poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) with 3-hydroxyvalerate (3HV) contents of 5.77 %, 6.08 %, 6.79 %, 6.845 %, for orange peels, pineapple peels, mango peels and banana peels substrates, respectively. The findings of this study suggest that fruit peels waste is a potential feedstock for sustainable production of PHAs by Halomonas alkalicola.

Time-dependent underwater interaction between polyhydroxyalkanoate coatings and functionalized surfaces

Polyhydroxyalkanoates (PHAs), a family of naturally occurring biodegradable polyester, are considered environmentally friendly alternatives to conventional commodity plastics derived from petrochemicals.; however, their molecular interaction in water has not been elucidated. Here, we investigated the surface- and contact time-dependent underwater interaction characteristics of poly(3-hydroxybutyrate-co-4-hydroxybutyrate) (P(3HB-co-4HB)), the most common PHA, using a surface forces apparatus (SFA). We found that PHA showed weak adhesion with functionalized surface and cohesion for a short-contact time (<30 mins) in the water. The adhesion to the functionalized surface was strong in the order of mica (negatively charged hydrophilic), APTES (positively charged hydrophilic), and PS (hydrophobic). However, the adhesive strength of PHA to the functionalized surfaces increased as contact time increased, which may be attributed to chain rearrangement, reorientation, or van der Waals forces of PHA in water. We also confirmed results similar to those for SFA by bulk testing on hydrophilic surfaces. As PHAs have attracted people’s attention as eco-friendly and biocompatible polymers, these results provide insights for the development of PHA-based composite, as well as for the biodegradation and fate of PHA post-use.

Production of Poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) by Haloferax mediterranei Using Candy Industry Waste as Raw Materials.

The haloarchaeon Haloferax mediterranei synthesizes poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) under unfavorable nutritional conditions without the addition of any precursor to the culture, which is an advantage compared to other microbial counterparts able to synthesize polyhydroxyalkanoates (PHA). PHBV is a biodegradable polymer showing physiochemical properties of biotechnological and biomedical interest and can be used as an alternative to plastics made from chemical synthesis (which are not environmentally friendly). The versatile metabolism of H. mediterranei makes the use of waste as a carbon source for cellular growth and PHA synthesis possible. In this work, cellular growth and the production and characterization of PHBV using two different types of confectionery waste were analyzed and compared with cellular growth and PHBV synthesis in a standard culture media with glucose of analytical grade as a carbon source. The PHBV granules produced were analyzed by TEM and the biopolymer was isolated and characterized by GC-MS, FTIR NMR, and DSC. The results reveal that H. mediterranei can use these two residues (R1 and R2) for pure PHBV production, achieving 0.256 and 0.983 g PHBV/L, respectively, which are among the highest yields so far described using for the first-time waste from the candy industry. Thus, a circular economy-based process has been designed to optimize the upscaling of PHBV production by using haloarchaea as cell factories and valorizing confectionery waste.

Biodegradability of oxidized films of polyhydroxyalkanoate copolymers containing 2-hydroxy-4-methylthiobutyrate unit in seawater

Polyhydroxyalkanoate (PHA) copolymers consisting of 3-hydroxybutyrate, 2-hydroxy-4-methylthiobutyrate (2H4MTB), and 2-hydroxy-4-methylvalerate were biosynthesized by recombinant Escherichia coli using L-methionine as the 2H4MTB precursor. The 2H4MTB unit contains a sulfide group in its side chain that can be oxidized to sulfoxide and sulfone groups by oxidants, thereby increasing the hydrophilicity of the polymer. The PHAs were biosynthesized at 3.9, 9.2, and 13.9 mol% 2H4MTB, and their polymer films were oxidized with hydrogen peroxide. The surface of the oxidized film was characterized using Fourier-transform infrared spectroscopy, Raman spectroscopy, and contact angle analysis. The oxidized films with 13.9 mol% 2H4MTB showed a 30° lower water contact angle than the non-oxidized films. To assess their marine biodegradability, the PHA films were immersed for 114 days in seawater continuously pumped from two depths (24 and 397 m) in Suruga Bay, Shizuoka, Japan. The weight loss of the films immersed in deep seawater was higher than that of those immersed in surface seawater. Additionally, there was a tendency for higher degradation of the oxidized films than that of the non-oxidized films, which was also confirmed by the biochemical oxygen demand test. In the surface morphology analysis by scanning electron microscopy, irregularities were observed in the degraded films, but their morphologies differed between the oxidized and non-oxidized films. Based on these observations, the biodegradation of the PHA films in seawater is discussed.

Overexpression of RuBisCO form I and II genes in Rhodopseudomonas palustris TIE-1 augments polyhydroxyalkanoate production heterotrophically and autotrophically.

With the rising demand for sustainable renewable resources, microorganisms capable of producing bioproducts such as bioplastics are attractive. While many bioproduction systems are well-studied in model organisms, investigating non-model organisms is essential to expand the field and utilize metabolically versatile strains. This investigation centers on Rhodopseudomonas palustris TIE-1, a purple non-sulfur bacterium capable of producing bioplastics. To increase bioplastic production, genes encoding the putative regulatory protein PhaR and the depolymerase PhaZ of the polyhydroxyalkanoate (PHA) biosynthesis pathway were deleted. Genes associated with pathways that might compete with PHA production, specifically those linked to glycogen production and nitrogen fixation, were deleted. Additionally, RuBisCO form I and II genes were integrated into TIE-1's genome by a phage integration system, developed in this study. Our results show that deletion of phaR increases PHA production when TIE-1 is grown photoheterotrophically with butyrate and ammonium chloride (NH4Cl). Mutants unable to produce glycogen or fix nitrogen show increased PHA production under photoautotrophic growth with hydrogen and NH4Cl. The most significant increase in PHA production was observed when RuBisCO form I and form I & II genes were overexpressed, five times under photoheterotrophy with butyrate, two times with hydrogen and NH4Cl, and two times under photoelectrotrophic growth with N2 . In summary, inserting copies of RuBisCO genes into the TIE-1 genome is a more effective strategy than deleting competing pathways to increase PHA production in TIE-1. The successful use of the phage integration system opens numerous opportunities for synthetic biology in TIE-1.IMPORTANCEOur planet has been burdened by pollution resulting from the extensive use of petroleum-derived plastics for the last few decades. Since the discovery of biodegradable plastic alternatives, concerted efforts have been made to enhance their bioproduction. The versatile microorganism Rhodopseudomonas palustris TIE-1 (TIE-1) stands out as a promising candidate for bioplastic synthesis, owing to its ability to use multiple electron sources, fix the greenhouse gas CO2, and use light as an energy source. Two categories of strains were meticulously designed from the TIE-1 wild-type to augment the production of polyhydroxyalkanoate (PHA), one such bioplastic produced. The first group includes mutants carrying a deletion of the phaR or phaZ genes in the PHA pathway, and those lacking potential competitive carbon and energy sinks to the PHA pathway (namely, glycogen biosynthesis and nitrogen fixation). The second group comprises TIE-1 strains that overexpress RuBisCO form I or form I & II genes inserted via a phage integration system. By studying numerous metabolic mutants and overexpression strains, we conclude that genetic modifications in the environmental microbe TIE-1 can improve PHA production. When combined with other approaches (such as reactor design, use of microbial consortia, and different feedstocks), genetic and metabolic manipulations of purple nonsulfur bacteria like TIE-1 are essential for replacing petroleum-derived plastics with biodegradable plastics like PHA.

Biosynthesis of Polyhydroalkanoates Doped with Silver Nanoparticles Using Pseudomonas putida and Pseudomonas aeruginosa for Antibacterial Polymer Applications.

In this study, the biosynthesis of polyhydroxyalkanoates (PHAs) was carried out using Pseudomonas putida and Pseudomonas aeruginosa. These PHAs were produced using reagent-grade glycerol and crude glycerol as the carbon sources. The objective was to compare the production of PHAs and to functionalize these polymers with silver nanoparticles to provide antibacterial properties for potential biomedical applications. The findings from the physical and chemical analyses confirmed the successful synthesis and extraction of PHAs, achieving comparable yields using both crude glycerol and reagent-grade glycerol as carbon sources across both strains. Approximately 16% higher PHAs production was obtained using Pseudomonas putida compared to Pseudomonas aeruginosa, and no significant difference was observed in the production rate of PHAs between the two carbon sources used, which means that crude glycerol could be utilized even though it has more impurities. Notably, PHAs functionalized with silver nanoparticles showed improved antibacterial effectiveness, especially those derived from reagent-grade glycerol and the Pseudomonas aeruginosa strain.

First evidence for temperature’s influence on the enrichment, assembly, and activity of polyhydroxyalkanoate-synthesizing mixed microbial communities

Polyhydroxyalkanoates (PHA) are popular biopolymers due to their potential use as biodegradable thermoplastics. In this study, three aerobic sequencing batch reactors were operated identically except for their temperatures, which were set at 15 °C, 35 °C, and 48 °C. The reactors were subjected to a feast–famine feeding regime, where carbon sources are supplied intermittently, to enrich PHA-accumulating microbial consortia. The biomass was sampled for 16S rRNA gene amplicon sequencing of both DNA (during the enrichment phase) and cDNA (during the enrichment and accumulation phases). All temperatures yielded highly enriched PHA-accumulating consortia. Thermophilic communities were significantly less diverse than those at low or mesophilic temperatures. In particular, Thauera was highly adaptable, abundant, and active at all temperatures. Low temperatures resulted in reduced PHA production rates and yields. Analysis of the microbial community revealed a collapse of community diversity during low-temperature PHA accumulation, suggesting that the substrate dosing strategy was unsuccessful at low temperatures. This points to future possibilities for optimizing low-temperature PHA accumulation.

Advances in Microbial Biotechnology for Sustainable Alternatives to Petroleum-Based Plastics: A Comprehensive Review of Polyhydroxyalkanoate Production.

The industrial production of polyhydroxyalkanoates (PHAs) faces several limitations that hinder their competitiveness against traditional plastics, mainly due to high production costs and complex recovery processes. Innovations in microbial biotechnology offer promising solutions to overcome these challenges. The modification of the biosynthetic pathways is one of the main tactics; allowing for direct carbon flux toward PHA formation, increasing polymer accumulation and improving polymer properties. Additionally, techniques have been implemented to expand the range of renewable substrates used in PHA production. These feedstocks are inexpensive and plentiful but require costly and energy-intensive pretreatment. By removing the need for pretreatment and enabling the direct use of these raw materials, microbial biotechnology aims to reduce production costs. Furthermore, improving downstream processes to facilitate the separation of biomass from culture broth and the recovery of PHAs is critical. Genetic modifications that alter cell morphology and allow PHA secretion directly into the culture medium simplify the extraction and purification process, significantly reducing operating costs. These advances in microbial biotechnology not only enhance the efficient and sustainable production of PHAs, but also position these biopolymers as a viable and competitive alternative to petroleum-based plastics, contributing to a circular economy and reducing the dependence on fossil resources.

Exploring the Processing Potential of Polylactic Acid, Polyhydroxyalkanoate, and Poly(butylene succinate-co-adipate) Binary and Ternary Blends.

Biodegradable and bio-based polymers, including polyhydroxyalkanoate (PHA), polylactic acid (PLA), and poly(butylene succinate-co-adipate) (PBSA), stand out as sustainable alternatives to traditional petroleum-based plastics for a wide range of consumer applications. Studying binary and ternary blends is essential to exploring the synergistic combinations and efficiencies of three distinct biopolyesters. A comprehensive evaluation of melt-extruded binary and ternary polymer blends of PHA, PLA, and PBSA was conducted. Scanning electron microscopy (SEM) analyses revealed a heterogeneous morphology characteristic of immiscible blends, with a predominant spherical inclusion morphology observed in the majority of the blends. An increased PBSA concentration led to an elevation in melt viscosity and elasticity across both ternary and binary blends. An increased PHA content reduced the viscosity, along with both storage and loss moduli in the blends. Moreover, a rise in PHA concentration within the blends led to increased crystallinity, albeit with a noticeable reduction in the crystallization temperature of PHA. PLA retained amorphous structure in the blends. The resultant bio-based blends manifested enhanced rheological and calorimetric traits, divergent from their pure polymer counterparts, highlighting the potential for optimizing material properties through strategic formulation adjustments.

Effect of mutation of phaC on carbon supply, extracellular polysaccharide production, and pathogenicity of Xanthomonas oryzae pv. oryzae

Xanthomonas oryzae pv. oryzae (Xoo) causes bacterial blight in rice. Polyhydroxyalkanoates (PHAs) consitute a diverse group of biopolyesters synthesized by bacteria under nutrient-limited conditions. The phaC gene is important for PHA polymerization. We investigated the effects of phaC gene mutagensis in Xoo strain PXO99A. The phaC gene knock-out mutant exhibited reduced swarming ability relative to that of the wild-type. Under conditions where glucose was the sole sugar source, extracellular polysaccharide (EPS) production by ΔphaC declined by 44.8%. ΔphaC showed weak hypersensitive response (HR) induction in the leaves of non-host Nicotiana tabacum, concomitant with downregulation of hpa1 gene expression. When inoculated in rice leaves by the leaf-clipping method, ΔphaC displayed reduced virulence in terms of lesion length compared with the wild-type strain. The complemented strain showed no significant difference from the wild-type strain, suggesting that the deletion of phaC in Xoo induces significant alterations in various physiological and biological processes. These include bacterial swarming ability, EPS production, transcription of hrp genes, and glucose metabolism. These changes are intricately linked to the energy utilization and virulence of Xoo during plant infection. These findings revealed involvement of phaC in Xoo is in the maintaining carbon metabolism by functioning in the PHA metabolic pathway.

Recent Advances in Food Waste Transformations into Essential Bioplastic Materials.

Lignocellulose is a major biopolymer in plant biomass with a complex structure and composition. It consists of a significant amount of high molecular aromatic compounds, particularly vanillin, syringeal, ferulic acid, and muconic acid, that could be converted into intracellular metabolites such as polyhydroxyalkanoates (PHA) and hydroxybutyrate (PHB), a key component of bioplastic production. Several pre-treatment methods were utilized to release monosaccharides, which are the precursors of the relevant pathway. The consolidated bioprocessing of lignocellulose-capable microbes for biomass depolymerization was discussed in this study. Carbon can be stored in a variety of forms, including PHAs, PHBs, wax esters, and triacylglycerides. From a biotechnology standpoint, these compounds are quite adaptable due to their precursors' utilization of hydrogen energy. This study lays the groundwork for the idea of lignocellulose valorization into value-added products through several significant dominant pathways.

Tailoring the structural and physicochemical properties of rice straw cellulose-based cryogels by cell-mediated polyhydroxyalkanoate deposition

This study presents a novel biotechnological approach for creating water vapor-resistant cryogels with improved integrity. Rice straw cellulose was transformed into nanofibrils through TEMPO-mediated oxidation and high-pressure homogenization. The resulting cryogels remained firm even when immersed in aqueous media, whose pores were used by live cell to deposit polyhydroxyalkanoate (PHA) particles inside them. This novel method allowed the compatibilization of PHA within the cellulosic fibers. As a consequence, the water sorption capacity was decreased by up to 6 times having just 4 % of PHA compared to untreated cryogels, preserving the cryogel density and elasticity. Additionally, this technique can be adapted to various bacterial strains and PHA types, allowing for further optimization. It was demonstrated that the amount and type of PHA (medium chain length and small chain length-PHA) used affects the properties for the cryogels, especially the water vapor sorption behavior and the compressive strength. Compared to traditional coating methods, this cell-mediated approach not only allows to distribute PHA on the surface of the cryogel, but also ensures polymer penetration throughout the cryogel due to bacterial self-movement. This study opens doors for creating cryogels with tunable water vapor sorption and other additional functionalities through the use of specialized PHA variants.

Large-scale cultivation of Synechocystis sp. PCC6803 for the production of Poly(3-hydroxybutyrate) and its potential applications in the manufacturing of bulk and medical prototypes

Polyhydroxyalkanoates (PHAs) are biopolymers produced by microorganisms under nutrient limiting conditions and in the presence of excess carbon source. PHAs have gained popularity as a sustainable alternative to traditional plastics. However, large scale production of PHAs is economically challenging due to the relatively high costs of organic carbon. Alternative options include using organisms capable of phototrophic or mixotrophic growth. This study aimed at the production of poly(3-hydroxybutyrate) P(3HB), a type of PHA, at pilot scale using the freshwater cyanobacterium Synechocystis sp. PCC6803. First, to identify optimal conditions for P(3HB) production from Synechocystis sp. PCC6803, different supplemental carbon source concentrations and salinity levels were tested at laboratory scale. The addition of 4 g/L acetate with no added NaCl led to P(3HB) accumulation of 10.7 % dry cell weight on the 28th day of cultivation. Although acetate additions were replicated in an outdoor 400 L serpentine photobioreactor, P(3HB) content was lower, implying uncontrolled conditions impact on biopolymer production efficiency. An optimized P(3HB) extraction methodology was developed to remove pigments, and the biopolymer was characterized and subjected to 3D printing (fused deposition modelling) to confirm its processability. This study thus successfully led to the large-scale production of P(3HB) using sustainable and environmentally friendly cyanobacterial fermentation.

Biodegradable Biobased Polymers: A Review of the State of the Art, Challenges, and Future Directions.

Biodegradable biobased polymers derived from biomass (such as plant, animal, marine, or forestry material) show promise in replacing conventional petrochemical polymers. Research and development have been conducted for decades on potential biodegradable biobased polymers such as polylactic acid (PLA), polyhydroxyalkanoates (PHAs), and succinate polymers. These materials have been evaluated for practicality, cost, and production capabilities as limiting factors in commercialization; however, challenges, such as the environmental limitations on the biodegradation rates for biodegradable biobased polymer, need to be addressed. This review provides a history and overview of the current development in the synthesis process and properties of biodegradable biobased polymers, along with a techno-commercial analysis and discussion on the environmental impacts of biodegradable biobased polymers. Specifically, the techno-commercial analysis focuses on the commercial potential, financial assessment, and life-cycle assessment of these materials, as well as government initiatives to facilitate the transition towards biodegradable biobased polymers. Lastly, the environmental assessment focuses on the current challenges with biodegradation and methods of improving the recycling process and reusability of biodegradable biobased polymers.

Biosynthesis of High Toughness Poly(3-Hydroxypropionate)-Based Block Copolymers With Poly(D-2-Hydroxybutyrate) and Poly(D-Lactate) Segments Using Evolved Monomer Sequence-Regulating Polyester Synthase.

This study synthesized poly(3-hydroxypropionate) [P(3HP)]-containing polyhydroxyalkanoate (PHA) block copolymers, P(3HP)-b-P[2-hydroxybutyrate (2HB)] and P(3HP)-b-P(D-lactate) (PDLA), using Escherichia coli. The cells expressing an evolved sequence-regulating PHA synthase, PhaCARNDFH, and propionyl-CoA transferase were cultured with the supplementation of the corresponding monomer precursors in the medium. The block structure of P(3HP)-b-PDLA was confirmed by proton nuclear magnetic resonance analysis and solvent fractionation. The molecular weights of the polymers were in the range of 0.8-2.8 × 105. The solvent-cast polymer films were subjected to isothermal treatment to promote phase separation and crystallization and were subsequently melt-quenched to produce an amorphous phase. The melt-quenched P(3HP)-b-P(2HB) film exhibited a high elongation at break (1153%), resulting in a toughness of 181 MJ/m3. The solvent-cast film of P(3HP)-b-65 mol% PDLA exhibited partial elastic deformation, in which the P(3HP) phase functioned as a soft segment. The melt-quenching of the polymer resulted in embrittlement presumably due to the high lactate fraction. Overall, the P(3HP)-based block copolymers exhibited several mechanical properties depending on the higher-order structure of the polymer and the properties of the P(2-hydroxyalkanoate) segments. This study findings show that P(3HP)-b-P(2HB) and P(3HP)-b-PDLA can function excellently if their microstructures are properly controlled.

Quantum modeling simulates nutrient effect of bioplastic polyhydroxyalkanoate (PHA) production in Pseudomonas putida

Polyhydroxyalkanoates (PHAs) could be used to make sustainable, biodegradable plastics. However, the precise and accurate mechanistic modeling of PHA biosynthesis, especially medium-chain-length PHA (mcl-PHA), for yield improvement remains a challenge to biology. PHA biosynthesis is typically triggered by nitrogen limitation and tends to peak at an optimal carbon-to-nitrogen (C/N) ratio. Specifically, simulation of the underlying dynamic regulation mechanisms for PHA bioprocess is a bottleneck owing to surfeit model complexity and current modeling philosophies for uncertainty. To address this issue, we proposed a quantum-like decision-making model to encode gene expression and regulation events as hidden layers by the general transformation of a density matrix, which uses the interference of probability amplitudes to provide an empirical-level description for PHA biosynthesis. We implemented our framework modeling the biosynthesis of mcl-PHA in Pseudomonas putida with respect to external C/N ratios, showing its optimization production at maximum PHA production of 13.81% cell dry mass (CDM) at the C/N ratio of 40:1. The results also suggest the degree of P. putida’s preference in channeling carbon towards PHA production as part of the bacterium’s adaptative behavior to nutrient stress using quantum formalism. Generic parameters (kD, kN and theta θ) obtained based on such quantum formulation, representing P. putida’s PHA biosynthesis with respect to external C/N ratios, was discussed. This work offers a new perspective on the use of quantum theory for PHA production, demonstrating its application potential for other bioprocesses.

Novel differential scanning calorimetry (DSC) application to select polyhydroxyalkanoate (PHA) producers correlating 3-hydroxyhexanoate (3-HHx) monomer with melting enthalpy.

Polyhydroxyalkanoate (PHA) is an environmental alternative to petroleum-based plastics because of its biodegradability. The polymer properties of PHA have been improved by the incorporation of different monomers. Traditionally, the monomer composition of PHA has been analyzed using gas chromatography (GC) and nuclear magnetic resonance (NMR), providing accurate monomer composition. However, sequential analysis of the thermal properties of PHA using differential scanning calorimetry (DSC) remains necessary, providing crucial insights into its thermal characteristics. To shorten the monomer composition and thermal property analysis, we directly applied DSC to the analysis of the obtained PHA film and observed a high correlation (r2 = 0.98) between melting enthalpy and the 3-hydroxyhexanoate (3-HHx) mole fraction in the polymer. A higher 3-HHx fraction resulted in a lower melting enthalpy as 3-HHx provided the polymer with higher flexibility. Based on this, we selected the poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) (P(3HB-co-3HHx)) producing strain from Cupriavidus strains that newly screened and transformed with vectors containing P(3HB-co-3HHx) biosynthetic genes, achieving an average error rate below 1.8% between GC and DSC results. Cupriavidus sp. BK2 showed a high 3-HHx mole fraction, up to 10.38mol%, with Tm(℃) = 171.5 and ΔH of Tm (J/g) = 48.0, simultaneously detected via DSC. This study is an example of the expansion of DSC for PHA analysis from polymer science to microbial engineering.