The degradation of plastics and the production of polyhydroxyalkanoates (PHA) / 生物工程学报

In recent years, the petroleum-based plastic pollution problem has been causing global attention. The idea of "degradation and up-cycling of plastics" was proposed for solving the environmental pollution caused by non-degradable plastics. Following this idea, plastics would be firstly degraded and then reconstructed. Polyhydroxyalkanoates (PHA) can be produced from the degraded plastic monomers as a choice to recycle among various plastics. PHA, a family of biopolyesters synthesized by many microbes, have attracted great interest in industrial, agricultural and medical sectors due to its biodegradability, biocompatibility, thermoplasticity and carbon neutrality. Moreover, the regulations on PHA monomer compositions, processing technology, and modification methods may further improve the material properties, making PHA a promising alternative to traditional plastics. Furthermore, the application of the "next-generation industrial biotechnology (NGIB)" utilizing extremophiles for PHA production is expected to enhance the PHA market competitiveness, promoting this environmentally friendly bio-based material to partially replace petroleum-based products, and achieve sustainable development with carbon-neutrality. This review summarizes the basic material properties, plastic upcycling via PHA biosynthesis, processing and modification methods of PHA, and biosynthesis of novel PHA.

Producción de plásticos biodegradables a partir de bacterias de hábitats salinos aisladas de la Laguna de Ayarza / Production of biodegradable plastics from saline habitats bacteria isolated from Laguna de Ayarza

La contaminación por plásticos petroquímicos es una grave amenaza para el medio ambiente que requiere im-plementar alternativas como los bioplásticos para lograr un desarrollo sostenible. Los polihidroxialcanoatos (PHA) son polímeros utilizados para la producción de plásticos biodegradables y que han llamado la atención como sustitutos de los plásticos de base fósil. Sin embargo, el costo de producción de los PHA constituye una barrera para su producción industrial a gran escala. Las de bacterias de hábitats salinos son microorganismos prometedores para la síntesis de PHA debido a sus características tales como altos requisitos de salinidad que previenen la contaminación microbiana, la alta presión osmótica intracelular que permite una fácil lisis celular para purificar los PHA y la capacidad para usar un amplio espectro de sustratos. La presente investigación planteó determinar las cepas nativas de bacterias halófilas y halotolerantes de la Laguna de Ayarza capaces de producir PHA, establecer la capacidad que tienen de utilizar residuos agrícolas para la producción de PHA y determinar su eficiencia. Esto se logró a través de la inoculación de las cepas productoras de PHA en medios de fermentación con pulpa de café, cáscaras de plátanos y salvado de trigo lo que permitió determinar las cepas más eficientes. Se encontró que las bacterias productoras de PHA pertenecen a las especies: Alcaligenes faecalis, Bacillus idriensis, Bacillus megaterium, Exiguobacterium acetylicum, E. aurantiacum, Pseudomonas cuatrocienegasensis y Sta-phylococcus capitis y que las cepas AP21-14, AP21-10 y AP21-03 mostraron los mejores resultados que podrían ser prometedores para la producción a nivel industrial.

Pollution by petrochemical plastics is a serious threat to the environment that requires the implementation of al-ternatives such as bioplastics to achieve sustainable development. Polyhydroxyalkanoates (PHAs) are polymers used for the production of biodegradable plastics and have drawn attention as substitutes for fossil-based plastics. However, the cost of producing PHAs constitutes a barrier to their large-scale industrial production. Bacteria from saline environments bacteria are promising microorganisms for PHA synthesis due to their characteristics such as high salinity requirements that prevent microbial contamination, high intracellular osmotic pressure that allows easy cell lysis to purify PHAs, and the ability to use a broad spectrum of substrates. This research project aimed to determine the native strains of halophilic and halotolerant bacteria from Laguna de Ayarza capable of producing PHA, establish their ability to use agricultural residues for the production of PHA, and determine their efficiency. This was achieved through the inoculation of the PHA-producing strains in fermentation media with coffee pulp, banana peels and wheat bran, which allowed determining the most efficient strains. It was found that the PHA-producing bacteria belong to the species: Alcaligenes faecalis, Bacillus idriensis, Bacillus mega-terium, Exiguobacterium acetylicum, E. aurantiacum, Pseudomonas cuatrocienegasensis and Staphylococcus capitis and that the strains AP21-14, AP21-10 and AP21-03 showed the best results that could be promising for production at an industrial level.

Halomonas uses short-chain fatty acids to synthesize polyhydroxyalkanoates / 生物工程学报

Halomonas can grow on diverse carbon sources. As it can be used for unsterile fermentation under high-salt conditions, it has been applied as a chassis for next-generation industrial biotechnology. Short-chain volatile fatty acids, including acetate, propionate, and butyrate, can be prepared from biomass and are expected to be novel carbon sources for microbial fermentation. Halomonas sp. TD01 and TD08 were subjected to shaking culture with 10-50 g/L butyrate, and they were found to effectively synthesize poly-3-hydroxybutyrate with butyrate as the carbon source. The highest yield of poly-3-hydroxybutyrate was achieved at butyrate concentration of 20 g/L (9.12 g/L and 7.37 g/L, respectively). Butyrate at the concentration > 20 g/L inhibited cell growth, and the yield of poly-3-hydroxybutyrate decreased to < 4 g/L when butyrate concentration was 50 g/L. Moreover, Halomonas sp. TD08 can accumulate the copolymer of 3-hydroxybutyrate and 3-hydroxyvalerate by using propionate and butyrate as carbon sources. However, propionate was toxic to cells. To be specific, when 2 g/L propionate and 20 g/L butyrate were simultaneously provided, cell dry weight and polymer titer were 0.83 g/L and 0.15 g/L, respectively. The addition of glycerol significantly improved cell growth and boosted the copolymer titer to 3.95 g/L, with 3-hydroxyvalerate monomer content of 8.76 mol%. Short-chain volatile fatty acids would be promising carbon sources for the production of polyhydroxyalkanoates by Halomonas.

Vibrio sp. ArtGut-C1, a polyhydroxybutyrate producer isolated from the gut of the aquaculture live diet Artemia (Crustacea)

BACKGROUND: Vibrio species display variable and plastic fitness strategies to survive and interact with multiple hosts, including marine aquaculture species that are severely affected by pathogenic Vibrios. The culturable Vibrio sp. strain ArtGut-C1, the focus of this study, provides new evidence of such phenotypic plasticity as it accumulates polyhydroxybutyrate (PHB), a biodegradable polymer with anti-pathogen activity, particularly in the marine larviculture phase. The strain was isolated from the gut of laboratory-reared Artemia individuals, the live diet and PHB carrier used in larviculture. Its main phenotypic properties, taxonomic status and genomic properties are reported based on the whole-genome sequencing. RESULTS: Vibrio sp. ArtGut-C1 yielded 72.6% PHB of cells' dry weight at 25 C. The genomic average nucleotide identity (ANI) shows it is closely related to V. diabolicus (ANI: 88.6%). Its genome contains 5,236,997- bp with 44.8% GC content, 3,710 protein-coding sequences, 96 RNA, 9 PHB genes functionally related to PHB metabolic pathways, and several genes linked to competing and colonizing abilities. CONCLUSIONS: This culturable PHB-accumulating Vibrio strain shows high genomic and phenotypic variability. It may be used as a natural pathogen biocontrol in the marine hatchery and as a potential cell factory for PHB production.

Effect of short-chain thioesterase deficiency on P(3HB-co-LA) biosynthesis in Escherichia coli / 生物工程学报

Polyhydroxyalkanoates (PHAs) have obtained much attention in biomaterial fields due to their similar physicochemical properties to those of the petroleum-derived plastics. Poly(3-hydroxybutyrate-co-lactate) [P(3HB-co-LA)] is one member of the PHAs family, and has better toughness and transparency compared to existing polylactic acid (PLA) and poly[(R)-3-hydroxybutyrate] [P(3HB)]. First, we confirmed the one-step biosynthesis of P(LA-co-3HB) with the lactate fraction of 23.8 mol% by introducing P(3HB-co-LA) production module into Escherichia coli MG1655. Then, the lactate fraction was increased to 37.2 mol% in the dld deficient strain WXJ01-03. The genes encoding the thioesterases, ydiI and yciA, were further knocked out, and the lactate fraction in the P(3HB-co-LA) was improved to 42.3 mol% and 41.1 mol% respectively. Strain WXJ03-03 with dld, ydiI and yciA deficient was used for the production of the LA-enriched polymer, and the lactate fraction was improved to 46.1 mol%. Notably, the lactate fraction in P(3HB-co-LA) from xylose was remarkably higher than from glucose, indicating xylose as a potent carbon source for P(3HB-co-LA) production. Therefore, the deficiency of thioesterase may be considered as an effective strategy to improve the lactate fraction in P(3HB-co-LA) in xylose fermentation.

A review on polyhydroxyalkanoates synthesis in activated sludge system: the effects of dissolved organic compounds by using anaerobic fermentation liquid from waste activated sludge / 生物工程学报

Polyhydroxyalkanoates (PHA) synthesis by activated sludge using volatile fatty acids (VFAs) in fermentation liquid of excess sludge as carbon source is a hotspot in the field of environmental biotechnology. However, there is no unified conclusion on the effects of non-VFAs, mainly dissolved organic matter (DOM), on PHA production. Thus, this critical review mainly introduces the main characteristics and common analysis methods of DOM in anaerobic fermentation liquid. The effects of DOM on PHA production are analyzed from the aspects of microbiology, metabolic regulation and sludge properties. The results of different studies showed that high concentration of DOM is bad for PHA production, but an appropriate amount of DOM is conducive to the stability of sludge properties, reducing the final PHA purification cost. Finally, suitable strategies were proposed to regulate the PHA synthesis by activated sludge with DOM for PHA production by anaerobic fermentation liquid.

Thirty years of metabolic engineering for biosynthesis of polyhydroxyalkanoates / 生物工程学报

Polyhydroxyalkanoate (PHA) is a family of biodegradable polyesters synthesized by microorganisms. It has various monomer structures and physical properties with broad application prospects. However, its large-scale production is still hindered by the high cost. In the past 30 years, metabolic engineering approach has been used to tune the metabolic flux, engineer and introduce pathways. The efficiency of PHA synthesis by microorganisms has been significantly improved, and the diversity of PHA monomer, structure and substrate have also been enriched. Meanwhile, by changing cell morphology and PHA particle size, more efficient downstream production process has achieved and PHA production costs have been reduced. In recent years, "Next generation industrial biotechnology" (NGIB) based on extremophiles, especially halophilic Halomonas spp., has been rapidly developed. NGIB has achieved the opening and continuous production of PHA, which simplifies the production process and saves energy and fresh water. Combined with metabolic engineering, Halomonas spp. can be transformed into low-cost production platform of numerous PHA. It is expected to improve the market competitiveness and promote the commercialization of PHA.

Engineering progress in microbial production of polyhydroxyalkanoates / 生物工程学报

Polyhydroxyalkanoates (PHAs) are polymers obtained by esterification of hydroxy fatty acid monomers. Due to similar mechanical characteristics of traditional petroleum-based plastics, 100% biodegradability and biocompatibility, PHAs are considered to be one of the most potential green materials. However, the application and promotion of PHAs as a green and environmentally friendly material are difficult because of the high production costs. This article focuses on the current methods to reduce production cost of PHAs effectively, such as cell morphology regulation, metabolic pathway construction, economic carbon source utilization and open fermentation technology development. Despite most research results are still limited in laboratory, the research methods and directions provide theoretical guidance for the industrial production of economic PHAs.

Research progress in polyhydroxyalkanoates (PHA) and their blend fibers / 生物工程学报

Polyhydroxyalkanoate (PHA) is a representative biodegradable polymer with more than 150 varieties and various properties. This article reviews the research status and potential applications of PHA, and introduces the properties of four-generation commercial PHA and its research progress in blend fibers with other biodegradable materials.

Microbial Synthesis and Characterization of Biodegradable Polyester Copolymers from Burkholderia Cepacia and Cupriavidus Necator Strains Using Crude Glycerol as Substrate

Abstract Polymers are materials of pronounced importance in the modern world, since they are massively present in everyday life, especially in the form of packaging. However, most of these materials are derived from non-renewable sources and their disposal generates large volumes of waste, which is extremely damaging to natural environments. In this context, microbial biopolymers appear as a powerful alternative in the substitution of several applications of synthetic plastics, causing less harm to the environment, as they are biodegradable and produced from renewable sources. In this study, evaluation and characterization of polyhydroxyalkanoates (PHAs) produced by Cupriavidus necator (IPT 026 and IPT 027) and Burkholderia cepacia (IPT 119 and IPT 400), using crude glycerol as substrate, were carried out (crude glycerol 15 g L-1, pH 7.0, 150 rpm, 72h). The substrate chemical composition was determined and all microorganisms tested were able to utilize it to synthesize PHA. C. necator IPT 026 exhibited the highest polymer production (1.52 ± 0.03 g L-1). B. cepacia strains produced low crystallinity PHA. All polyesters synthesized exhibited long chain length polymers with low polydispersity and initial thermal degradation temperatures superior to 300°C. The microorganism strains and the substrate composition highly affected PHAs synthesis, composition and thermochemical characteristics.

Variation analysis of bacterial polyhydroxyalkanoates production using saturated and unsaturated hydrocarbons

ABSTRACT Polyhydroxyalkanoates (PHA) are efficient, renewable and environment friendly polymeric esters. These polymers are synthesized by a variety of microbes under stress conditions. This study was carried out to check the suitability of waste frying oil in comparison to other oils for economical bioplastic production. Six bacterial strains were isolated and identified as Bacillus cereus (KF270349), Klebsiella pneumoniae (KF270350), Bacillus subtilis (KF270351), Brevibacterium halotolerance (KF270352), Pseudomonas aeruginosa (KF270353), and Stenotrophomonas rhizoposid (KF270354) by ribotyping. All strains were PHA producers so were selected for PHA synthesis using four different carbon sources, i.e., waste frying oil, canola oil, diesel and glucose. Extraction of PHA was carried out using sodium hypochlorite method and maximum amount was detected after 72 h in all cases. P. aeruginosa led to maximum PHA production after 72 h at 37 °C and 100 rpm using waste frying oil that was 53.2% PHA in comparison with glucose 37.8% and cooking oil 34.4%. B. cereus produced 40% PHA using glucose as carbon source which was high when compared against other strains. A significantly lesser amount of PHA was recorded with diesel as a carbon source for all strains. Sharp Infrared peaks around 1740-1750 cm-1 were present in Fourier Transform Infrared spectra that correspond to exact position for PHA. The use of waste oils and production of poly-3hydroxybutyrate-co-3hydroxyvalerate (3HB-co-3HV) by strains used in this study is a good aspect to consider for future prospects as this type of polymer has better properties as compared to PHBs.

Evaluation of short-chain-length polyhydroxyalkanoate accumulation in Bacillus aryabhattai

Abstract This study was focused on the polyhydroxybutyrate (PHB) accumulation property of Bacillus aryabhattai isolated from environment. Twenty-four polyhydroxyalkanoate (PHA) producers were screened out from sixty-two environmental bacterial isolates based on Sudan Black B colony staining. Based on their PHA accumulation property, six promising isolates were further screened out. The most productive isolate PHB10 was identified as B. aryabhattai PHB10. The polymer production maxima were 3.264 g/L, 2.181 g/L, 1.47 g/L, 1.742 g/L and 1.786 g/L in glucose, fructose, maltose, starch and glycerol respectively. The bacterial culture reached its stationary and declining phases at 18 h and 21 h respectively and indicated growth-associated PHB production. Nuclear Magnetic Resonance (NMR) spectra confirmed the material as PHB. The material has thermal stability between 30 and 140 °C, melting point at 170 °C and maximum thermal degradation at 287 °C. The molecular weight and poly dispersion index of the polymer were found as 199.7 kDa and 2.67 respectively. The bacterium B. aryabhattai accumulating PHB up to 75% of cell dry mass utilizing various carbon sources is a potential candidate for large scale production of bacterial polyhydroxybutyrate.

Bioconversion of mixed free fatty acids to poly-3-hydroxyalkanoates by Pseudomonas putida BET001 and modeling of its fermentation in shake flasks

Background: The paper reports on the utilization of palm kernel oil (PKO) as a low cost renewable substrate for medium-chain-length poly-3-hydroxyalkanoates (mcl-PHA) production by Pseudomonas putida BET001. Investigation on the effects of selected key variables on growth, mixed free fatty acids consumption and mcl-PHA production by the bacterial culture in the shaken flask system were carried out along with its kinetic modeling. Results: The biomass production, fatty acids consumption and mcl-PHA production were found favorable when the strain was cultured in mineral medium at pH 6-7,28°C, aeration surface-to-volume ratio of 0.4 x 10(6) m-1, 250 rpm agitation rate for 48 h. Mcl-PHA production by this strain showed mixed growth and non-growth associated components as described by Luedeking-Piret kinetic model. Conclusion: The findings of this study provided add to the literature on key variables in for achieving good microbial growth and mcl-PHA production in shake flasks culture. In addition, suitable kinetic model to describe cultivation in this system was also presented.

Preparation and characterization of polyhydroxyalkanoate bioplastics with antibacterial activity / 生物工程学报

Polyhydroxyalkanoates (PHAs), as a novel class of biopolymer, are attracting more attention due to their diverse material properties and environment-independent biodegradability. Here we report the preparation of PHA exhibiting efficient antibacterial activity by embedding Nisin, a food additive generally recognized as safe, into poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) (PHBHHx), a type of PHA with high biocompatibility. We first prepared Nisin-containing PHBHHx films using solvent casting method. Confocal laser scanning microscopy analysis showed that a well-mixed integrated structure of the films with an even distribution of the Nisin particles in the PHBHHx matrices. Then the antimicrobial activity of PHBHHx/Nisin films against Micrococcus luteus was quantified on agar plate by measuring the size of inhibition zone. Cultivation in liquid media further confirmed the releasing of Nisin from the films and the long-time antibacterial activity. Results showed that the threshold of Nisin concentration for long-time and effective inhibition against bacteria growth is 25 μg/g. These results altogether establish a technological foundation for the application of PHA in biomedicine and food industry.

Current status of bio-based materials industry in China / 生物工程学报

In recent years, bio-based materials are becoming a new dominant industry leading the scientific and technological innovation, and economic development of the world. We reviewed the new development of bio-based materials industry in China, analyzed the entire market of bio-based materials products comprehensively, and also stated the industry status of bio-based chemicals, such as lactic acid, 1,3-propanediol, and succinic acid; biodegradable bio-based polymers, such as co-polyester of diacid and diol, polylactic acid, carbon dioxide based copolymer, polyhydroxyalknoates, polycaprolactone, and thermoplastic bio-based plastics; non-biodegradable bio-based polymers, such as bio-based polyamide, polytrimethylene terephthalate, bio-based polyurethane, and bio-based fibers.

Progress on polyhydroxyalkanoates (PHA) / 生物工程学报

Microbial polyhydroxyalkanoates (PHA) has developed with more diversity and more advanced manufacturing technology. Diversity has now been reflected by diverse monomers, diverse structures and diverse polymerization modes, giving the concept of "PHAome". In addition, the application of synthetic biology and the development of seawater-based biotechnology reduce the production cost of PHA, making PHA more economically competitive. Some examples of commercialized PHA products are described here. Besides, PHA with high value added applications has been exploited.

Biomanufactured polyhydroxyalkanoates (PHA) modification: a review / 生物工程学报

In this review, we presented the industrial status of biomanufactured polyhydroxyalkanoates (PHA), including poly (3-hydroxybutyrate) (PHB), poly (3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV), poly (3-hydroxybutyrate-co-4-hydroxybutyrate) (P3/4HB)), and poly (3-hydroxybutyrate-3-hydroxycaproate) (PHBH). A lot of modification studies, aimed at solving problems of poor thermal stability, narrow processing window and other drawbacks of PHA, are discussed. The properties of PHA can be optimized by using proper modification method, in order to expand its applications.

Research and industrialization of biobased materials in China / 生物工程学报

This paper reviews the research and commercialization progresses of biobased polymeric materials including polyhydroxyalkanoates (PHA), polylactides (PLA), poly (butylene succinate) (PBS) and its monomer succinate, and CO2 copolymer poly (propylene carbonate), especially these efforts made in China.

Volatile fatty acids influence on the structure of microbial communities producing PHAs

Polyhydroxyalkanoates (PHAs) can be produced by microorganisms and are a biodegradable alternative to fossil-fuel based plastics. Currently, the focus is on reducing production costs by exploring alternative substrates for PHAs production, and on producing copolymers which are less brittle than monomers. Accordingly, this study used a substrate consisting of wastewater from waste-glycerol fermentation, supplemented with different amounts of acetic and propionic acids. These substrates were used to feed mixed microbial communities enriched from activated sludge in a sequencing batch reactor. A reactor supplemented with 2 mL of acetic acid produced 227.8 mg/L of a homopolymer of hydroxybutyrate (3HB); 4 mL of acetic acid produced 279.8 mg/L 3HB; whereas 4 mL of propionic acid produced 673.0 mg/L of a copolymer of 3HB and 3HV (hydroxyvalerate). Ribosomal Intergenic Spacer Analysis (RISA) was used to show the differences between the communities created in the reactors. Thauera species predominated in biomass that produced 3HB; Paracoccus denitrificans in the biomass that produced 3HB-co-3HV. Because P. denitrificans produced the more desirable copolymer, it may be advantageous to promote its growth in PHAs-producing reactors by adding propionate.

Optimization of biodegradable plastic production on sugar cane molasses in Enterobacter sp. SEL2

Contaminated environments have a large number of bacteria which can accumulate PHA as their energy reserves. Out of 54 isolated bacterial strains from three groups of contaminated sites 48 were found PHA positive. The sites were grouped on the basis of the type of carbon sources i.e. sugars, fatty acids and much diverse type. Strains MFD5, MFD11, UML3, USL2, SEL2, SEL3, SEL10 and PFW1 produced 69.9 ± 0.29, 75.27 ± 0.45, 65.43 ± 0.1, 72.54 ± 0.27, 76.61 ± 0.28, 61.81 ± 0.05, 71.16 ± 0.09 and 74.92 ± 0.5 percent of PHA to their constant cell weight (CCW) respectively in PHA detection media supplemented with 2% glucose. Molasses, whey, crumbs hydrolysate and palm oil were checked as inexpensive carbon sources. Molasses alone could supply the required nutrients for growth and PHA production. Strain SEL2 produced 47.36 ± 0.45% PHA using 2% molasses at 37 °C and pH 7.0. Upon production optimization the best accumulation (80.95 ± 0.01%) was observed in PHA detection media with 0.2% nitrogen source, 3% molasses, pH 5.0 and 37 °C by the strain SEL2. The overall effect of the presence of increased molasses concentration in the media was positive it increased the accumulation period till 72 h. Enterobacter sp. SEL2 (JF901810) is first time being reported for PHA production.