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

Biosynthesis of biodegradable plastic, poly(3HB-co-3HP), using methane as sole carbon source in metabolically engineered type II methanotroph, Methylosinus trichosporium OB3b

We report a biosynthetic method for producing poly(3-hydroxybutyrate-co-3-hydroxypropionate) [P(3HB-co-3HP)] copolymer from methane alone; we developed a 3-hydroxypropionate (3HP) biosynthetic pathway starting from methane in Methylosinus trichosporium OB3b and overexpressed 3HP-CoA transferase to optimize 3HP incorporation into P(3HB-co-3HP) copolymers. Upon comparing the β-alanine and malonyl-CoA pathways, we discovered that the latter showed greater potential for the formation of 3HP monomers. In addition, we examined the activities of 3HP-CoA synthetases from three distinct sources and found that the enzyme from Metallosphaera sedula was the most effective for 3HP incorporation. Using methane as the sole carbon source in a shake-flask culture, we developed recombinant strains and found that the best strain was OB3b-MCRM-3S, which formed a P(3HB-co-3HP) copolymer, up to 25.62 % of the biomass, with a maximum 3HP level of 9.02 mol%. Our research demonstrates the successful production of a biopolymer, the P(3HB-co-3HP) copolymer, via methane bioconversion using methanotrophs.

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.

Medium Chain Length Polyhydroxyalkanoate Production by Engineered Pseudomonas gessardii Using Acetate-formate as Carbon Sources

Production of medium chain length polyhydroxyalkanoate (mcl-PHA) was attempted using Pseudomonas gessardii NIBRBAC000509957, which was isolated from Sunchang, Jeollabuk-do, Republic of Korea (35°24'27.7"N, 127°09'13.0"E) and effectively utilized acetate and formate as carbon sources. We first evaluated the utilization of acetate as a carbon source, revealing optimal growth at 5 g/L acetate. Then, formate was supplied to the acetate minimal medium as a carbon source to enhance cell growth. After overexpressing the acetate and formate assimilation pathway enzymes, this strain grew at a significantly higher rate in the medium. As this strain naturally produces PHA, it was further engineered metabolically to enhance mcl-PHA production. The engineered strain produced 0.40 g/L of mcl-PHA with a biomass content of 30.43% in fed-batch fermentation. Overall, this strain can be further developed to convert acetate and formate into valuable products.

Artificial carbon assimilation: From unnatural reactions and pathways to synthetic autotrophic systems

Synthetic biology is being increasingly used to establish novel carbon assimilation pathways and artificial autotrophic strains that can be used in low-carbon biomanufacturing. Currently, artificial pathway design has made significant progress from advocacy to practice within a relatively short span of just over ten years. However, there is still huge scope for exploration of pathway diversity, operational efficiency, and host suitability. The accelerated research process will bring greater opportunities and challenges. In this paper, we provide a comprehensive summary and interpretation of representative one-carbon assimilation pathway designs and artificial autotrophic strain construction work. In addition, we propose some feasible design solutions based on existing research results and patterns to promote the development and application of artificial autotrophy.

Copolymers and Blends Based on 3-Hydroxybutyrate and 3-Hydroxyvalerate Units

This review presents a comprehensive update of the biopolymer poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV), emphasizing its production, properties, and applications. The overall biosynthesis pathway of PHBV is explored in detail, highlighting recent advances in production techniques. The inherent physicochemical properties of PHBV, along with its degradation behavior, are discussed in detail. This review also explores various blends and composites of PHBV, demonstrating their potential for a range of applications. Finally, the versatility of PHBV-based materials in multiple sectors is examined, emphasizing their increasing importance in the field of biodegradable polymers.

Plastisphere characterization in habitat of the highly endangered Shinisaurus crocodilurus: Bacterial composition, assembly, function and the comparison with surrounding environment

Plastisphere is a new niche for microorganisms that complicate the ecological effects of plastics, and may profoundly influence biodiversity and habitat conservation. The DaGuishan National Nature Reserve, one of the largest habitats of the highly endangered crocodile lizard (Shinisaurus crocodilurus), is experiencing plastic pollution without sufficient attention. Here, plastisphere collected from captive tanks of crocodile lizards in this nature reserve was characterized for the first time. Three types of plastic (PE-PP, PE1, and PE2) together with the surrounding water and soil samples, were collected, and 16S rRNA sequencing technology was used to characterize the bacterial composition. The results demonstrated that plastisphere was driven by stochastic process and had a distinct bacterial community with higher diversity than that in surrounding water (p < 0.05). Bacteria related to nitrogen and carbon cycles (Pseudomonas psychrotolerans, Methylobacterium-Methylorubrum) were more abundant in plastisphere than in water or soil (p < 0.05). More importantly, plastics recruited pathogens and those bacteria function in antibiotic resistant genes (ARGs) coding. Bacteria related to polymer degradation also proliferated in plastisphere, especially Bacillus subtilis with a fold change of 42.01. The PE2 plastisphere, which had the lowest diversity and was dominated by Methylobacterium-Methylorubrum differed from PE 1 and PE-PP plastispheres totally. Plastics' morphology and aquatic nutrient levels contributed to the heterogeneity of different plastispheres. Overall, this study demonstrated that plastispheres diversify in composition and function, affecting ecosystem services directly or indirectly. Pathogens and bacteria related to ARGs expression enriched in the plastisphere should not be ignored because they may threaten the health of crocodile lizards by increasing the risk of infection. Plastic pollution control should be included in conservation efforts for crocodile lizards. This study provides new insights into the potential impacts of plastisphere, which is important for ecological risk assessments of plastic pollution in the habitats of endangered species.

Recent trends of biotechnological production of polyhydroxyalkanoates from C1 carbon sources

Growing concerns over the use of limited fossil fuels and their negative impacts on the ecological niches have facilitated the exploration of alternative routes. The use of conventional plastic material also negatively impacts the environment. One such green alternative is polyhydroxyalkanoates, which are biodegradable, biocompatible, and environmentally friendly. Recently, researchers have focused on the utilization of waste gases particularly those belonging to C1 sources derived directly from industries and anthropogenic activities, such as carbon dioxide, methane, and methanol as the substrate for polyhydroxyalkanoates production. Consequently, several microorganisms have been exploited to utilize waste gases for their growth and biopolymer accumulation. Methylotrophs such as Methylobacterium organophilum produced highest amount of PHA up to 88% using CH₄ as the sole carbon source and 52-56% with CH₃OH. On the other hand Cupriavidus necator, produced 71-81% of PHA by utilizing CO and CO₂ as a substrate. The present review shows the potential of waste gas valorization as a promising solution for the sustainable production of polyhydroxyalkanoates. Key bottlenecks towards the usage of gaseous substrates obstructing their realization on a large scale and the possible technological solutions were also highlighted. Several strategies for PHA production using C1 gases through fermentation and metabolic engineering approaches are discussed. Microbes such as autotrophs, acetogens, and methanotrophs can produce PHA from CO₂, CO, and CH₄. Therefore, this article presents a vision of C1 gas into bioplastics are prospective strategies with promising potential application, and aspects related to the sustainability of the system.

Levulinic Acid-Inducible and Tunable Gene Expression System for Methylorubrum extorquens

Methylorubrum extorquens AM1 is an efficient platform strain possessing biotechnological potential in formate- and methanol-based single carbon (C1) bioeconomy. Constitutive expression or costly chemical-inducible expression systems are not always desirable. Here, several glucose-, xylose-, and levulinic acid (LA)-inducible promoter systems were assessed for the induction of green fluorescent protein (GFP) as a reporter protein. Among them, the LA-inducible gene expression system (HpdR/P _hpdH ) showed a strong expression of GFP (51-fold) compared to the control. The system was induced even at a low concentration of LA (0.1 mM). The fluorescence intensity increased with increasing concentrations of LA up to 20 mM. The system was tunable and tightly controlled with meager basal expression. The maximum GFP yield obtained using the system was 42 mg/g biomass, representing 10% of the total protein content. The efficiency of the proposed system was nearly equivalent (90%-100%) to that of the widely used strong promoters such as P _mxaF and P _L/O4 . The HpdR/P _hpdH system worked equally efficiently in five different strains of M. extorquens. LA is a low-cost, renewable, and sustainable platform chemical that can be used to generate a wide range of products. Hence, the reported system in potent strains of M. extorquens is highly beneficial in the C1-biorefinery industry to produce value-added products and bulk chemicals.

Strategies for Biosynthesis of C1 Gas-derived Polyhydroxyalkanoates: A review

Biosynthesis of polyhydroxyalkanoates (PHAs) from C1 gases is highly desirable in solving problems such as climate change and microplastic pollution. PHAs are biopolymers synthesized in microbial cells and can be used as alternatives to petroleum-based plastics because of their biodegradability. Because 50% of the cost of PHA production is due to organic carbon sources and salts, the utilization of costless C1 gases as carbon sources is expected to be a promising approach for PHA production. In this review, strategies for PHA production using C1 gases through fermentation and metabolic engineering are discussed. In particular, autotrophs, acetogens, and methanotrophs are strains that can produce PHA from CO₂, CO, and CH₄. In addition, integrated bioprocesses for the efficient utilization of C1 gases are introduced. Biorefinery processes from C1 gas into bioplastics are prospective strategies with promising potential and feasibility to alleviate environmental issues.

A shortcut to carbon-neutral bioplastic production: Recent advances in microbial production of polyhydroxyalkanoates from C1 resources

Since the 20th century, plastics that are widely being used in general life and industries are causing enormous plastic waste problems since improperly discarded plastics barely degrade and decompose. Thus, the demand for polyhydroxyalkanoates (PHAs), biodegradable polymers with material properties similar to conventional petroleum-based plastics, has been increased so far. The microbial production of PHAs is an environment-friendly solution for the current plastic crisis, however, the carbon sources for the microbial PHA production is a crucial factor to be considered in terms of carbon-neutrality. One‑carbon (C1) resources, such as methane, carbon monoxide, and carbon dioxide, are greenhouse gases and are abundantly found in nature and industry. C1 resources as the carbon sources for PHA production have a completely closed carbon loop with much advances; i) fast carbon circulation with direct bioconversion process and ii) simple fermentation procedure without sterilization as non-preferable nutrients. This review discusses the biosynthesis of PHAs based on C1 resource utilization by wild-type and metabolically engineered microbial host strains via biorefinery processes.

Engineering of Shewanella marisflavi BBL25 for biomass-based polyhydroxybutyrate production and evaluation of its performance in electricity production

Polyhydroxybutyrate (PHB) is a biodegradable plastic with physical properties similar to petrochemically derived plastics. Here, Shewanella marisflavi BBL25 was engineered by inserting the pLW487 vector containing polyhydroxyalkanoates synthesis genes from Ralstonia eutropha H16. Under optimal conditions, the engineered S. marisflavi BBL25 produced 1.99 ± 0.05 g/L PHB from galactose. The strain showed high tolerance to various inhibitors and could utilize lignocellulosic biomass for PHB production. When barley straw hydrolysates were used as a carbon source, PHB production was 3.27 ± 0.19 g/L. In addition, PHB production under the microbial fuel cell system was performed to confirm electricity coproduction. The maximum electricity current output density was 1.71 mA/cm², and dry cell weight (DCW) and PHB production were 11.4 g/L and 6.31 g/L, respectively. Our results demonstrated PHB production using various lignocellulosic biomass and the feasibility of PHB and electricity production, simultaneously, and it is the first example of PHB production in engineered Shewanella.