Production enhancement of poly(3-hydroxybutyrate-co-3-hydroxyvalerate) in Halogeometricum borinquense, characterization of the bioplastic and desalination of the bioreactor effluent

Unlocking the potential of microbes: Concomitant production of polyhydroxyalkanoates and carotenoids

The escalating environmental concerns and depletion of crude oil resources have catalyzed interest in biologically derived polymers, particularly biodegradable ones such as polyhydroxyalkanoates. However, the high production costs associated with polyhydroxyalkanoates, driven by raw material expenses, stringent production conditions and low yields, hinder their widespread adoption. A potential strategy to mitigate these costs involves the production of PHAs and other high-value bioproducts, such as carotenoids simultaneously in microbial systems, utilizing shared metabolic pathways. Carotenoids, known for their antioxidant properties and applications in the food, cosmetics and pharmaceutical industries, offer substantial market potential. This review presents a comprehensive overview of the current progress in polyhydroxyalkanoate and carotenoid co-production, explores the co-synthesis pathways, addresses the challenges involved and explores the future prospects of this integrated bioprocess. By diversifying the product portfolio and optimizing microbial production systems, the co-production strategy could pave the way for more sustainable and economically viable bioplastics.

Application of Bacillus cereus for synthesis of polyhydroxyalkanoates from industrial corn starch residue

Starch hydrolysate from corn is typically employed as a carbon source for citric acid production by Aspergillus niger. Enzymatic or acid hydrolysis of corn starch generates a corn starch residue (CSR), which represents a potential bio-fermentation carbon source. In addition, polyhydroxyalkanoates (PHAs) can be used as an alternative to traditional petrochemical plastics. In this study, the potential applications of CSR in microbial PHA production were investigated. Two Bacillus cereus strains, MG1 and MQ1, were isolated based on their ability to grow with CSR as the sole carbon source and their capacity for PHA accumulation. After introducing key genes involved in the PHA synthesis pathway and optimizing fermentation conditions, the PHA content of MG2 reached 61.61 % of the cell dry weight (CDW), representing the highest PHA content (CDW%) in B. cereus. To the best of our knowledge, this is the first report of PHA synthesis from CSR in B. cereus and provides a novel approach for the rational utilization of CSR.

Innovations in poly(3-hydroxybutyrate-co-3-hydroxyvalerate) and nanocomposites for sustainable food packaging via biochemical biorefinery platforms: A comprehensive review

The substantial build-up of non-biodegradable plastic waste from packaging sector not only poses severe environmental threats but also hastens the depletion of natural petroleum-based resources. Presently, poly (3-hydroxybutyrate-co-3-hydroxy valerate) (PHBV), received enormous attention as ideal alternatives for such traditional petroleum-derived plastics based on their biocompatibility and superior mechanical properties. However, high cost of such copolymer, due to expensive nature of feedstock, inefficient microbial processes and unfavorable downstream processing strategies restricts its large-scale commercial feasibility in the packaging sector. This review explores merits and challenges associated with using potent agricultural and industrial waste biomasses as sustainable feedstocks alongside improved fermentation and downstream processing strategies for the biopolymer in terms of biorefinery concept. Despite PHBV's attractive properties, its inherent shortcomings like weak thermal stability, poor mechanical properties, processability difficulty, substantial hydrophobicity and comparatively higher water vapor permeability (WVP) demand the development of its composites based on the application. Based on this fact, the review assessed properties and potential applications of PHBV-based composite materials having natural raw materials, nanomaterials and synthetic biodegradable polymers. Besides, the review also enlightens sustainability, future prospects, and challenges associated with PHBV-based composites in the field of food packaging while considering insights about economic evaluation and life cycle assessment.

Microbial production of poly(3-hydroxybutyrate-co-3-hydroxyvalerate), from lab to the shelf: A review

Polyhydroxyalkanoates (PHAs) are natural biopolyesters produced by microorganisms that represent one of the most promising candidates for the replacement of conventional plastics due to their complete biodegradability and advantageous material properties which can be modulated by varying their monomer composition. Poly(3-hydroxybutyrate-co-3-hydroxyvalerate) [P(3HB-co-3HV)] has received particular research attention because it can be synthesized based on the same microbial platform developed for poly(3-hydroxybutyrate) [P(3HB)] without much modification, with as high productivity as P(3HB). It also offers more useful mechanical and thermal properties than P(3HB), which broaden its application as a biocompatible and biodegradable polyester. However, a significant commercial disadvantage of P(3HB-co-3HV) is its rather high production cost, thus many studies have investigated the economical synthesis of P(3HB-co-3HV) from structurally related and unrelated carbon sources in both wild-type and recombinant microbial strains. A large number of metabolic engineering strategies have also been proposed to tune the monomer composition of P(3HB-co-3HV) and thus its material properties. In this review, recent metabolic engineering strategies designed for enhanced production of P(3HB-co-3HV) are discussed, along with their current status, limitations, and future perspectives.

Evaluation of polyhydroxyalkanoate (PHA) synthesis by Pichia sp. TSLS24 yeast isolated in Vietnam

Following the rising concern on environmental issues caused by conventional fossil-based plastics and depleting crude oil resources, polyhydroxyalkanoates (PHAs) are of great interest by scientists and biodegradable polymer market due to their outstanding properties which include high biodegradability in various conditions and processing flexibility. Many polyhydroxyalkanoate-synthesizing microorganisms, including normal and halophilic bacteria, as well as algae, have been investigated for their performance in polyhydroxyalkanoate production. However, to the best of our knowledge, there is still limited studies on PHAs-producing marine yeast. In the present study, a halophilic yeast strain isolated from Spratly Island in Vietnam were investigated for its potential in polyhydroxyalkanoate biosynthesis by growing the yeast in Zobell marine agar medium (ZMA) containing Nile red dye. The strain was identified by 26S rDNA analysis as Pichia kudriavzevii TSLS24 and registered at Genbank database under code OL757724. The amount of polyhydroxyalkanoates synthesized was quantified by measuring the intracellular materials (predicted as poly(3-hydroxybutyrate) -PHB) by gravimetric method and subsequently confirmed by Fourier transform infrared (FTIR) spectroscopic and nuclear magnetic resonance (NMR) spectroscopic analyses. Under optimal growth conditions of 35 °C and pH 7 with supplementation of glucose and yeast extract at 20 and 10 gL^-1, the isolated strain achieved poly(3-hydroxybutyrate) content and concentration of 43.4% and 1.8 gL^-1 after 7 days of cultivation. The poly(3-hydroxybutyrate) produced demonstrated excellent biodegradability with degradation rate of 28% after 28 days of incubation in sea water.

Metabolic engineering for biosynthesis of poly(3-hydroxybutyrate-co-3-hydroxyvalerate) from glucose and propionic acid in recombinant Escherichia coli

In this study, novel polyhydroxyalkanoate (PHA)-associated genes (phaCp and phaABp) cloned from Propylenella binzhouense L72^T were expressed in Escherichiacoli cells for PHA production, and the recombinant strains were used to analyze PHA yields with various substrates. The highest poly (3-hydroxybutyrate-co-3-hydroxy-valerate) (PHBV) yield (1.06 g/L) and cell dry weight (3.31 g/L) in E. coli DH5α/ΔptsG-CpABp were achieved by using glucose and propionicacid as substrates. Structural verification of PHBV produced by E. coli DH5α/ΔptsG-CpABp was performed to evaluate the characteristics of the polymers using Fourier transform infrared spectroscopy and nuclear magnetic resonance analysis. In addition, the X-ray diffraction results showed improved crystallinity of PHBV, and thermogravimetric analysis showed good thermal stability of 298 °C. The above findings indicated that the expression of phaCp and phaABp genes resulted in improved PHBV synthesis activity, and the polymer had better performance at higher processing temperatures.

Biosynthesis of poly(3-hydroxybutyrate-co-3-hydroxyvalerate) in metabolically recombinant Escherichia coli

In this study, a phaC_R gene encoding PHA synthase was identified in Rhodoligotrophos defluvii which was adjacent to β-ketothiolase encoded by phaA_R gene and acetoacetyl-CoA reductase encoded by phaB_R gene. Amino acid comparison of PhaC_R showed the highest homology of 65.98% with PhaC of R. appendicifer, while its homology with typical class I PHA synthase in Cupriavidus necator was only 42.54%. PHA synthesis genes were then transformed into E. coli harboring phaCAB_R and phaC_RAB_C which were cultured with 15 g/L glucose respectively, and 20.46 wt% and 16.95 wt% of CDW for poly(3-hydroxybutyrate) (PHB) were accumulated respectively. To further explore the effect of substrate specificity for PHA production, the ptsG gene was then deleted and 15 g/L glucose and 1.5 g/L propionate were co-employed as carbon sources, which enabled the synthesis of poly(3HB-co-3HV) copolymer. As a result, poly(3HB-co-3HV) was accumulated up to 24.74 wt% of CDW, and the highest content of 3-hydroxyvalerate (3HV) was 10.86 mol%. The T_d5 was 260 °C, which implied that it possessed good thermal stability, and the M_w of GPC in recombinant strains were between 22 and 26 × 10⁴ g/mol, and the highest PDI was 3.771. The structure of poly (3HB-co-3HV) copolymer was determined through ¹H NMR analysis.

Polyhydroxyalkanoates and biochar from green macroalgal Ulva sp. biomass subcritical hydrolysates: Process optimization and a priori economic and greenhouse emissions break-even analysis

Although macroalgae biomass is an emerging sustainable feedstock for biorefineries, the optimum process parameters for their hydrolysis and fermentation are still not known. In the present study, the simultaneous production of polyhydroxyalkanoates (PHA) and biochar from green macroalgae Ulva sp. is examined, applying subcritical water hydrolysis and Haloferax mediterranei fermentation. First, the effects of temperature, treatment time, salinity, and solid load on the biomass and PHA productivity were optimized following the Taguchi method. Hydrolysis at 170 °C, 20 min residence time, 38 g L^-1 salinity with a seaweed solid load of 5% led to the maximum PHA yield of 0.104 g g^-1Ulva and a biochar yield of 0.194 ± 1.23 g g^-1Ulva. Second, the effect of different initial culture densities on the biomass and PHA productivity was studied. An initial culture density of 50 g L^-1 led to the maximum volumetric PHA productivity of 0.024 ± 0.002 g L^-1 h^-1 with a maximum PHA content of 49.38 ± 0.3% w/w Sensitivity analysis shows that within 90% confidence, the annual PHA production from Ulva sp. is 148.14 g PHA m^-2 year^-1 with an annual biochar production of 42.6 g m^-2 year^-1. Priori economic and greenhouse gas break-even analyses of the process were done to estimate annual revenues and allowable greenhouse gas emissions. The study illustrates that PHA production from seaweed hydrolysate using extreme halophiles coupled to biochar production could become a benign and promising step in a marine biorefinery.

Metabolic engineering of Methylorubrum extorquens AM1 for poly (3-hydroxybutyrate-co-3-hydroxyvalerate) production using formate

Formate is a promising environmentally friendly and sustainable feedstock synthesized from syngas or carbon dioxide. Methylorubrum extorquens is a type II methylotroph that can use formate as a carbon source. It accumulates polyhydroxyalkanoates (PHAs) inside the cell, mainly producing poly-3-hydroxybutyrate (PHB), a degradable biopolymer. Owing to its high melting point and stiff nature, however, mechanical property improvement is warranted in the form of copolymerization. To produce the PHA copolymer, poly (3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV), the endogenous gene phaC was deleted and the pathway genes bktB, phaJ1, and phaC2, with broader substrate specificities, were heterologously expressed. To improve the incorporation of 3-hydroxyvalerate (3HV), the expression level of bktB was improved by untranslated region (UTR) engineering, and the endogenous gene phaA was deleted. The engineered M. extorquens produced PHBV with 8.9% 3HV using formate as the sole carbon source. In addition, when propionate and butyrate were supplemented, PHBVs with 3HV portions of up to 70.6% were produced. This study shows that a PHBV copolymer with a high proportion of 3HV can be synthesized using formate, a C1 carbon source, through metabolic engineering and supplementation with short-chain fatty acids.

Established and advanced approaches for recovery of microbial polyhydroxyalkanoate (PHA) biopolyesters from surrounding microbial biomass

Downstream processing for recovery of microbial polyhydroxyalkanoate (PHA) biopolyesters from biomass constitutes an integral part of the entire PHA production chain; beside the feedstocks used for cultivation of PHA-production strains, this process is currently considered the major cost factor for PHA production.

Besides economic aspects, PHA recovery techniques need to be sustainable by avoiding excessive use of (often precarious!) solvents, other hazardous chemicals, non-recyclable compounds, and energy. Moreover, the applied PHA recovery method is decisive for the molecular mass and purity of the obtained product, and the achievable recovery yield. In addition to the applied method, also the PHA content in biomass is decisive for the feasibility of a selected technique. Further, not all investigated recovery techniques are applicable for all types of PHA (crystalline versus amorphous PHA) and all PHA-producing microorganisms (robust versus fragile cell structures).

The present review shines a light on benefits and shortcomings of established solvent-based, chemical, enzymatic, and mechanical methods for PHA recovery. Focus is dedicated on innovative, novel recovery strategies, encompassing the use of “green” solvents, application of classical “PHA anti-solvents” under pressurized conditions, ionic liquids, supercritical solvents, hypotonic cell disintegration for release of PHA granules, switchable anionic surfactants, and even digestion of non-PHA biomass by animals.

The different established and novel techniques are compared in terms of PHA recovery yield, product purity, impact on PHA molar mass, scalability to industrial plants, and demand for chemicals, energy, and time.