Biosynthesis and characterization of copolymer poly(3HB-co-3HV) from saponified Jatropha curcas oil by Pseudomonas oleovorans

Investigations into the characterization, degradation, and applications of biodegradable polymers by mass spectrometry

Biodegradable polymers have been getting more and more attention because of their contribution to the plastic pollution environmental issues and to move towards a circular economy. Nevertheless, biodegradable materials still exhibit various disadvantages restraining a widespread use in the market. Therefore, additional research efforts are required to improve their performance. Mass spectrometry (MS) affords a relevant contribution to optimize biodegradable polymer synthesis, to confirm macromolecular structures, to examine along the time the progress of degradation processes and highlight advantages and drawbacks in the extensive applications. This review aims to provide an overview of the MS investigations carried out to support the synthesis of biodegradable polymers, with helpful information on undesirable products or polymerization mechanism, to understand deterioration pathways by the structure of degradation products and to follow drug release and pharmacokinetic. Additionally, it summarizes MS studies addressed on environmental and health issues related to the extensive use of plastic materials, that is, potential migration of additives or microplastics identification and quantification. The paper is focused on the most significant studies relating to synthetic and microbial biodegradable polymers published in the last 15 years, not including agro-polymers such as proteins and polysaccharides.

Formation of polyhydroxyalkanoates using agro and industrial waste as a substrate - a review

In the present scenario, rising environmental concerns of non-biodegradable plastic pollution and depletion of petroleum based raw materials lead to the development of biopolymers. The biodegradability of biopolymers gives them a specific advantage for the environmental concerns. Polyhydroxyalkanoates (PHAs) are a type of biopolymers which are synthesized by microorganisms. Although there are different substrates available in pure forms which are currently used in the production of PHA, 40% of production cost depends on the expensive substrate which is a major disadvantage and make it far from many applications. The use of an inexpensive carbon source which is high in organic matter content such as waste streams of process industries can make this process viable and diminish PHA production cost. This study explores the current research initiatives on various agricultural and industrial waste feedstocks, formulations and processing conditions for producing PHA in a way that is both inexpensive and beneficial to the environment. The creation of fermentation conditions and metabolic engineering techniques for promoting microbial growth and PHA synthesis were also discussed in the review.

Methods of Analyses for Biodegradable Polymers: A Review

Biodegradable polymers are materials that can decompose through the action of various environmental microorganisms, such as bacteria and fungi, to form water and carbon dioxide. The biodegradability characteristics have led to a growing demand for the accurate and precise determination of the degraded polymer composition. With the advancements in analytical product development, various analytical methods are available and touted as practical and preferable methods of bioanalytical techniques, which enable the understanding of the complex composition of biopolymers such as polyhydroxyalkanoates and poly(lactic acid). The former part of this review discusses the definition and examples of biopolymers, followed by the theory and instrumentation of analytical methods applicable to the analysis of biopolymers, such as physical methods (SEM, TEM, weighing analytical balance, etc.), chromatographic methods (GC, THM-GC, SEC/GPC), spectroscopic methods (NMR, FTIR, XRD, XRF), respirometric methods, thermal methods (DSC, DTA, TGA), and meta-analysis. Special focus is given to the chromatographic methods, because this is the routine method of polymer analysis. The aim of this review is to focus on the recent developments in the field of biopolymer analysis and instrument application to analyse the various types of biopolymers.

Optimized cell growth and poly(3-hydroxybutyrate) synthesis from saponified spent coffee grounds oil

Abstract

Spent coffee ground (SCG) oil is an ideal substrate for the biosynthesis of polyhydroxyalkanoates (PHAs) by Cupriavidus necator. The immiscibility of lipids with water limits their bioavailability, but this can be resolved by saponifying the oil with potassium hydroxide to form water-soluble fatty acid potassium salts and glycerol. Total saponification was achieved with 0.5 mol/L of KOH at 50 °C for 90 min. The relationship between the initial carbon substrate concentration (C₀) and the specific growth rate (µ) of C. necator DSM 545 was evaluated in shake flask cultivations; crude and saponified SCG oils were supplied at matching initial carbon concentrations (C₀ = 2.9–23.0 g/L). The Han-Levenspiel model provided the closest fit to the experimental data and accurately described complete growth inhibition at 32.9 g/L (C₀ = 19.1 g/L) saponified SCG oil. Peak µ-values of 0.139 h⁻¹ and 0.145 h⁻¹ were obtained with 11.99 g/L crude and 17.40 g/L saponified SCG oil, respectively. Further improvement to biomass production was achieved by mixing the crude and saponified substrates together in a carbon ratio of 75:25% (w/w), respectively. In bioreactors, C. necator initially grew faster on the mixed substrates (µ = 0.35 h⁻¹) than on the crude SCG oil (µ = 0.23 h⁻¹). After harvesting, cells grown on crude SCG oil obtained a total biomass concentration of 7.8 g/L and contained 77.8% (w/w) PHA, whereas cells grown on the mixed substrates produced 8.5 g/L of total biomass and accumulated 84.4% (w/w) of PHA.

Key points

• The bioavailability of plant oil substrates can be improved via saponification.

• Cell growth and inhibition were accurately described by the Han-Levenpsiel model.

• Mixing crude and saponified oils enable variation of free fatty acid content.

Control of a pyrimidine ribonucleotide salvage pathway in Pseudomonas oleovorans

The control of a pyrimidine ribonucleotide salvage pathway in the bacterium Pseudomonas oleovorans ATCC 8062 was studied. This bacterium is important for its ability to synthesize polyesters as well as for its increasing clinical significance in humans. The pyrimidine salvage pathway enzymes pyrimidine nucleotide N-ribosidase and cytosine deaminase were investigated in P. oleovorans ATCC 8062 under selected culture conditions. Initially, the effect of carbon source on the two pyrimidine salvage enzymes in ATCC 8062 cells was examined and it was observed that cell growth on the carbon source succinate generally produced higher enzyme activities than did glucose or glycerol as a carbon source when ammonium sulfate served as the nitrogen source. Using succinate as a carbon source, growth on dihydrouracil as nitrogen source caused a 1.9-fold increase in the pyrimidine nucleotide N-ribosidase activity and a 4.8-fold increase in cytosine deaminase activity compared to the ammonium sulfate-grown cells. Growth of ATCC 8062 cells on cytosine or dihydrothymine as a nitrogen source elevated deaminase activity by more than double that observed for ammonium sulfate-grown cells. The findings indicated a relationship between this pyrimidine salvage pathway and the pyrimidine reductive catabolic pathway since growth on dihydrouracil appeared to increase the degradation of the pyrimidine ribonucleotide monophosphates to uracil. The uracil produced could be degraded by the pyrimidine base reductive catabolic pathway to β-alanine as a source of nitrogen. This investigation could prove helpful to future work examining the metabolic relationship between pyrimidine salvage pathways and pyrimidine reductive catabolism in pseudomonads.

Optimization of Propagation Medium for Enhanced Polyhydroxyalkanoate Production by Pseudomonas oleovorans

Polyhydroxyalkanoates (PHAs) represent a promising alternative to commercially used petroleum-based plastics. Pseudomonas oleovorans is a natural producer of medium-chain-length PHA (mcl-PHA) under cultivation conditions with nitrogen limitation and carbon excess. Two-step cultivation appears to be an efficient but more expensive method of PHA production. Therefore, the aim of this work was to prepare a minimal synthetic medium for maximum biomass yield and to optimize selected independent variables by response surface methodology (RSM). The highest biomass yield (1.71 ± 0.04 g/L) was achieved in the optimized medium containing 8.4 g/L glucose, 5.7 g/L sodium ammonium phosphate and 35.4 mM phosphate buffer. Under these conditions, both carbon and nitrogen sources were completely consumed after 48 h of the cultivation and the biomass yield was 1.7-fold higher than in the conventional medium recommended by the literature. This approach demonstrates the possibility of using two-stage PHA cultivation to obtain the maximum amount of biomass and PHA.

Polyhydroxyalkanoates (PHAs) Production from Volatile Fatty Acids (VFAs) from Organic Wastes by Pseudomonas oleovorans

This study aimed to investigate the production of polyhydroxyalkanoates (PHAs), a biodegradable polymer from organic wastes by Pseudomonas oleovorans. Volatile fatty acids (VFAs) from acidogenic fermentations of chicken manure (VFAs-CM) and potato peels (VFAs-PP), rich in organic matter majorly acetic (49.9%), butyric (15%) and propionic acids (11.1%) were utilized as substrates for microbial processes. During 72 h of cultivations, samples were withdrawn at intervals and analyzed for cell growth parameters, PHAs accumulation and polymeric properties. The highest biopolymer accumulation (0.39 g PHAs/g DCW) was achieved at 48 h of cultivation from medium containing VFAs-PP as the sole source of carbon. On characterization, the produced biopolymers were shown to be semi-crystalline of carbonyl C=O group. Additionally, thermogravimetric analysis (TGA) showed that the produced biopolymers demonstrated the capability to withstand thermal degradation above prescribed temperatures at which cross-linking isomerization reaction occurs, which is a vital property denoting the thermal stability of biopolymer.

Can Polyhydroxyalkanoates Be Produced Efficiently From Waste Plant and Animal Oils?

Polyhydroxyalkanoates (PHAs) are a potential replacement for some petrochemical-based plastics. PHAs are polyesters synthesized and stored by various bacteria and archaea in their cytoplasm as water-insoluble inclusions. PHAs are usually produced when the microbes are cultured with nutrient-limiting concentrations of nitrogen, phosphorus, sulfur, or oxygen and excess carbon sources. Such fermentation conditions have been optimized by industry to reduce the cost of PHAs produced commercially. Industrially, these biodegradable polyesters are derived from microbial fermentation processes utilizing various carbon sources. One of the major constraints in scaling-up PHA production is the cost of the carbon source metabolized by the microorganisms. Hence, cheap and renewable carbon substrates are currently being investigated around the globe. Plant and animal oils have been demonstrated to be excellent carbon sources for high yield production of PHAs. Waste streams from oil mills or the used oils, which are even cheaper, are also used. This approach not only reduces the production cost for PHAs, but also makes a significant contribution toward the reduction of environmental pollution caused by the used oil. Advancements in the genetic and metabolic engineering of bacterial strains have enabled a more efficient utilization of various carbon sources, in achieving high PHA yields with specified monomer compositions. This review discusses recent developments in the biosynthesis and classification of various forms of PHAs produced using crude and waste oils from the oil palm and fish industries. The biodegradability of the PHAs produced from these oils will also be discussed.

Enhanced polyhydroxyalkanoate (PHA) production from the organic fraction of municipal solid waste by using mixed microbial culture

BACKGROUND

In Europe, almost 87.6 million tonnes of food waste are produced. Despite the high biological value of food waste, traditional management solutions do not consider it as a precious resource. Many studies have reported the use of food waste for the production of high added value molecules. Polyhydroxyalkanoates (PHAs) represent a class of interesting bio-polyesters accumulated by different bacterial cells, and has been proposed for production from the organic fraction of municipal solid waste (OFMSW). Nevertheless, until now, no attention has been paid to the entire biological process leading to the transformation of food waste to organic acids (OA) and then to PHA, getting high PHA yield per food waste unit. In particular, the acid-generating process needs to be optimized, maximizing OA production from OFMSW. To do so, a pilot-scale Anaerobic Percolation Biocell Reactor (100 L in volume) was used to produce an OA-rich percolate from OFMSW which was used subsequently to produce PHA.

RESULTS

The optimized acidogenic process resulted in an OA production of 151 g kg^-1 from fresh OFMSW. The subsequent optimization of PHA production from OA gave a PHA production, on average, of 223 ± 28 g kg^-1 total OA fed. Total mass balance indicated, for the best case studied, a PHA production per OFMSW weight unit of 33.22 ± 4.2 g kg^-1 from fresh OFMSW, corresponding to 114.4 ± 14.5 g kg^-1 of total solids from OFMSW. PHA composition revealed a hydroxybutyrate/hydroxyvalerate (%) ratio of 53/47 and Mw of 8∙10⁵ kDa with a low polydispersity index, i.e. 1.4.

CONCLUSIONS

This work showed how by optimizing acidic fermentation it could be possible to get a large amount of OA from OFMSW to be then transformed into PHA. This step is important as it greatly affects the total final PHA yield. Data obtained in this work can be useful as the starting point for considering the economic feasibility of PHA production from OFMSW by using mixed culture.

Microbial production of polyhydroxyalkanoates (PHAs) and its copolymers: A review of recent advancements

Traditional mineral oil based plastics are important commodity to enhance the comfort and quality of life but the accumulation of these plastics in the environment has become a major universal problem due to their low biodegradation. Solution to the plastic waste management includes incineration, recycling and landfill disposal methods. These processes are very time consuming and expensive. Biopolymers are important alternatives to the petroleum-based plastics due to environment friendly manufacturing processes, biodegradability and biocompatibility. Therefore use of novel biopolymers, such as polylactide, polysaccharides, aliphatic polyesters and polyhydroxyalkanoates is of interest. PHAs are biodegradable polyesters of hydroxyalkanoates (HA) produced from renewable resources by using microorganisms as intracellular carbon and energy storage compounds. Even though PHAs are promising candidate for biodegradable polymers, however, the production cost limit their application on an industrial scale. This article provides an overview of various substrates, microorganisms for the economical production of PHAs and its copolymers. Recent advances in PHAs to reduce the cost and to improve the performance of PHAs have also been discussed.

Overexpression of succinyl-CoA synthase for poly (3-hydroxybutyrate-co-3-hydroxyvalerate) production in engineered Escherichia coli BL21(DE3)

AIM

This study aims to increase the 3-hydroxyvalerate (3HV) fraction in poly(3-hydroxybutyrate-co-3-hydroxyvalerate) [P(HB-co-HV)] using succinyl-CoA synthase.

METHODS AND RESULTS

Escherichia coli YH090, a polyhydroxyalkonate (PHA)-producing strain, was further engineered for overexpression of succinyl-CoA synthase genes (sucCD), and examined for P(HB-co-HV) copolymer production in the presence of various precursor molecules using mixture analysis. Glycerol, succinate and propionate were screened as important factors for controlling intracellular PHA accumulation and monomer composition. Glycerol concentrations exerted the greatest influence on the overall biomass concentration and the intracellular PHA content, while propionate concentrations in the presence of succinate influenced the 3HV content of the copolymer. Mixture analysis also demonstrated that the engineered strain has the capacity to accumulate up to 80% of its cell dry weight (CDW) as PHA with a variable fraction of 3HV monomer (maximum of 72 wt %) depending on the controlled conditions.

CONCLUSIONS

Propionate is the principal precursor for 3HV monomer in P(HB-co-HV) biopolymer and its utilization requires conversion to propionyl-CoA. Engineered E. coli YHY99, overexpressing sucCD genes, leads to an increase of the succinyl-CoA pool, which enhances the conversion rate of propionate by providing a CoA supply to other acyltransferase enzymes that have a role in propionate utilization.

SIGNIFICANCE AND IMPACT OF THE STUDY

Engineered E. coli YHY99 was able to utilize propionate with a 4·5-fold increase in rate, as compared to the control strain, and resulted in the synthesis of a copolymer with high 3HV monomer content.

Valorization of fatty acids-containing wastes and byproducts into short- and medium-chain length polyhydroxyalkanoates

Olive oil distillate (OOD), biodiesel fatty acids-byproduct (FAB) and used cooking oil (UCO) were tested as inexpensive carbon sources for the production of polyhydroxyalkanoates (PHA) with different composition using twelve bacterial strains. OOD and FAB were exploited for the first time as alternative substrates for PHA production. UCO, OOD and FAB were used by Cupriavidus necator and Pseudomonas oleovorans to synthesize the homopolymer poly-3-hydroxybutyrate, while Pseudomonas resinovorans and Pseudomonas citronellolis produced mcl-PHA polymers mainly composed of hydroxyoctanoate and hydroxydecanoate monomers. The highest polymer content in the biomass was obtained for C. necator (62 wt.%) cultivated on OOD. Relatively high mcl-PHA content (28-31 wt.%) was reached by P. resinovorans cultivated in OOD. This study shows, for the first time, that OOD is a promising substrate for PHA production since it gives high polymer yields and allows for the synthesis of different polymers (scl- or mcl-PHA) by selection of the adequate strains.

Biotechnological Production of Polyhydroxyalkanoates: A Review on Trends and Latest Developments

Polyhydroxyalkanoates (PHA) producers have been reported to reside at various ecological niches which are naturally or accidently exposed to high organic matter or growth limited conditions such as dairy wastes, hydrocarbon contaminated sites, pulp and paper mill wastes, agricultural wastes, activated sludges of treatment plants, rhizosphere, and industrial effluents. Few among them also produce extracellular by-products like rhamnolipids, extracellular polymeric substances, and biohydrogen gas. These sorts of microbes are industrially important candidates for the reason that they can use waste materials of different origin as substrate with simultaneous production of valuable bioproducts including PHA. Implementation of integrated system to separate their by-products (intracellular and extracellular) can be economical in regard to production. In this review, we have discussed various microorganisms dwelling at different environmental conditions which stimulate them to accumulate carbon as polyhydroxyalkanoates granules and factors influencing its production and composition. A brief aspect on metabolites which are produced concomitantly with PHA has also been discussed. In conclusion, exploring of capabilities like of dual production by microbes and use of wastes as renewable substrate under optimized cultural conditions either in batch or continuous process can cause deduction in present cost of bioplastic production from stored PHA granules.

Synthesis of poly-(3-hydroxybutyrate-co-12 mol % 3-hydroxyvalerate) by Bacillus cereus FB11: its characterization and application as a drug carrier

The synthesis of microbial polyhydroxyalkanoate is investigated in this work for it potential application as drug carrier for cancer therapy. The bacterial isolate Bacillus cereus FB11 has synthesized poly-(3-hydroxybutyrate-co-3-hydroxyvalerate) copolymer under nutrient stress conditions using glucose as a sole carbon source. The FTIR spectrum of the purified copolymer showed the characteristic absorption bands at 1,719, 1,260 and 2,931 cm(-1) attributing to C=O, C-O stretching and C-H vibrations, respectively. The result of (1)H-NMR confirmed that it was composed of 88 mol % of 3-hydroxybutyrate and 12 mol % of 3-hydroxyvalerate monomeric subunits. The nanoparticles were fabricated from copolymer and used as a carrier for anticancer drug ellipticine. The in vitro drug release studies showed that % inhibition of A549 cancer cell line receiving ellipticine loaded poly-(3-hydroxybutyrate-co-3-hydroxyvalerate) nanoparticles was two-fold higher in comparison to ellipticine alone. This drug delivery system offers exciting possibilities for cancer therapy by increasing the bioavailability of anti-neoplastic drug to the tumor site.

Biosynthesis and characterization of polyhydroxyalkanoates copolymers produced by Pseudomonas putida Bet001 isolated from palm oil mill effluent

The biosynthesis and characterization of medium chain length poly-3-hydroxyalkanoates (mcl-PHA) produced by Pseudomonas putida Bet001 isolated from palm oil mill effluent was studied. The biosynthesis of mcl-PHA in this newly isolated microorganism follows a growth-associated trend. Mcl-PHA accumulation ranging from 49.7 to 68.9% on cell dry weight (CDW) basis were observed when fatty acids ranging from octanoic acid (C_8∶0) to oleic acid (C_18∶1) were used as sole carbon and energy source. Molecular weight of the polymer was found to be ranging from 55.7 to 77.7 kDa. Depending on the type of fatty acid used, the ¹H NMR and GCMSMS analyses of the chiral polymer showed a composition of even and odd carbon atom chain with monomer length of C4 to C14 with C8 and C10 as the principal monomers. No unsaturated monomer was detected. Thermo-chemical analyses showed the accumulated PHA to be semi-crystalline polymer with good thermal stability, having a thermal degradation temperature (T_d) of 264.6 to 318.8 (±0.2) ^oC, melting temperature (T_m) of 43. (±0.2) ^oC, glass transition temperature (T_g) of −1.0 (±0.2) ^oC and apparent melting enthalpy of fusion (ΔH_f) of 100.9 (±0.1) J g⁻¹.