Synthetic plastics are pivotal in our current lifestyle and therefore, its accumulation is a major concern for environment and human health. Petroleum-derived (petro-)polymers such as polyethylene ...(PE), polyethylene terephthalate (PET), polyurethane (PU), polystyrene (PS), polypropylene (PP), and polyvinyl chloride (PVC) are extremely recalcitrant to natural biodegradation pathways. Some microorganisms with the ability to degrade petro-polymers under
conditions have been isolated and characterized. In some cases, the enzymes expressed by these microbes have been cloned and sequenced. The rate of polymer biodegradation depends on several factors including chemical structures, molecular weights, and degrees of crystallinity. Polymers are large molecules having both regular crystals (crystalline region) and irregular groups (amorphous region), where the latter provides polymers with flexibility. Highly crystalline polymers like polyethylene (95%), are rigid with a low capacity to resist impacts. PET-based plastics possess a high degree of crystallinity (30-50%), which is one of the principal reasons for their low rate of microbial degradation, which is projected to take more than 50 years for complete degraded in the natural environment, and hundreds of years if discarded into the oceans, due to their lower temperature and oxygen availability. The enzymatic degradation occurs in two stages: adsorption of enzymes on the polymer surface, followed by hydro-peroxidation/hydrolysis of the bonds. The sources of plastic-degrading enzymes can be found in microorganisms from various environments as well as digestive intestine of some invertebrates. Microbial and enzymatic degradation of waste petro-plastics is a promising strategy for depolymerization of waste petro-plastics into polymer monomers for recycling, or to covert waste plastics into higher value bioproducts, such as biodegradable polymers via mineralization. The objective of this review is to outline the advances made in the microbial degradation of synthetic plastics and, overview the enzymes involved in biodegradation.
A gene encoding the intracellular PHA depolymerase of the saprotrophic soil bacterium, Pseudomonas putida LS46 was cloned and expressed in Escherichia coli. The gene has an open reading frame of 852 ...bp, encoding a protein of 283 amino acids with a predicted molecular mass of 31.5 kDa. The protein, PhaZLS46, has a α/β-hydrolase fold and a catalytic triad (serine-histidine-aspartic acid), which is found in all members of the lipase/esterase enzyme family. The catalytic serine is present in a Gx1Sx2G sequence motif, also known as lipase box, with the x1 and x2 positions occupied by valine101 and trypophan103, respectively. The purified recombinant enzyme was active optimally at 30 °C and pH 6.0, and displayed a broad-substrate specificity, with the ability to hydrolyze medium chain polyhydroxyalkanoates, as well as various para-nitrophenyl alkanoates. The enzyme also showed depolymerase activity against petroleum-based polymers, such as polyethylene succinate PES and poly(ϵ-caprolactone) PCL, making it extremely useful for biodegradation. Our results suggest that PhaZLS46 from P. putida LS46 represents a new subgroup of intracellular mcl-PHA depolymerases. The degradation products of PhaZLS46 on different polymers were analyzed using GPC. The ESI-MS analysis revealed that PhaZLS46 belongs to exohydrolases capable of releasing monomers as major reaction products (R-hydroxyalkanoic acids, RHAs) upon PHA degradation. The extracted RHAs (3-hydroxyoctanoic acids) formed by the action of enzyme on PHO had improved antibacterial action against the tested strain (E. coli BL21), forming clear zones of growth inhibition on agar diffusion plates with the minimal inhibitory concentration value (MIC) of 4 mM.
•The mcl-PHA depolymerase from P. putida LS46 (PhaZLS46) was characterized.•PhaZLS46 was significantly different compared to other known mcl-PHA depolymerases.•PhaZLS46 has a broad substrate specificity and acts as an exo-hydrolase.•Gel Permeation Chromatography confirmed degradation of a variety of polymers.•RHAs generated by PhaZLS46 had antibacterial action against E. coli.
Polypyrrole (PPy) nanomaterials have been synthesized with varying concentrations (10–40 mM) of anionic surfactant camphor sulphonic acid (CSA) using the chemical polymerization method, and then ...utilized for electromagnetic interference (EMI) shielding applications in the X-band of the microwave frequency range (8.2–12.4 GHz). An observable systematic change in the morphology of the prepared PPy has been noted, with highly aggregated globules transforming into fibular-like structures with an average diameter of approximately 80–120 nm as the CSA concentration increased. Raman and Fourier-transform infrared (FTIR) measurements indicate an increase in the relative intensities of the bipolaronic to polaronic bands, suggesting an improved conjugation of PPy with increasing CSA concentration. The electrical conductivity at room temperature has also been found to increase significantly, from 2.55 S/cm to 35.80 S/cm, as the concentration of CSA surfactant increased from 10 mM to 40 mM. Additionally, the shielding effectiveness (SE) for reflection (SE
R
), SE for absorption (SE
A
), and total SE (SE
T
) have been found to increase with increasing CSA concentration in PPy. The SE
T
values have been found exceeding 35 dB throughout the X-band of the microwave region in PPy nanomaterials with CSA concentrations ≥ 20 mM. It has been observed that CSA-directed polypyrrole exhibits high electrical conductivity, where the SE for absorption (SE
A
) dominates over the SE for reflection (SE
R
). This study suggests that the properties of PPy can be easily tailored for its potential utilization in the fabrication of various EMI shielding devices with improved performance.
Polyaniline (PAni) thin film has been synthesized using chemical oxidation route to be used as highly sensitive and selective ammonia (NH
3
) sensors. In situ dip-coating chemical polymerization ...method has been used to grow PAni thin films on glass substrates. The morphological and structural properties of deposited thin film have been examined by scanning electron microscopy (SEM), X-ray diffraction (XRD), Raman spectroscopy and Fourier-transform infrared (FTIR) spectroscopy techniques. Raman and FTIR analysis confirm the successful growth of PAni with long-chain conjugation, whereas SEM micrograph reveals the growth of nanofibrous structured polyaniline. An amorphous structure of the prepared polyaniline with perpendicular periodicity of the conjugated polymer chains has been observed through XRD analysis. The ammonia gas sensing properties, in terms of change in electrical resistance, of the prepared thin film sensor have been investigated at room temperature for different concentrations (25–150 ppm) of ammonia. The deposited film has sensitivity as high as 245% and selectivity (%) of ~ 67% towards ammonia gas (at 150 ppm). The gas sensing response of the deposited film is found to be increased with increasing concentration of ammonia and the observed behaviour is well corroborated with modified Freundlich’s sensitivity versus chemical concentration relation. The effect of humidity on the sensing response and other parameters associated with the figure of merits of sensor like response time, recovery time, selectivity, stability etc. have also been studied. The compensation of charge carriers, i.e. polarons and bipolarons, under the electron donating ammonia gas is considered to be the mechanism of gas sensing for the deposited PAni film. The synthesized PAni thin film sensor with low cost, high sensitivity, selectivity and durability can be utilized for the development of industrial ammonia sensor.
Biodegradation of short-chain-length polyhydroxyalkanoates (scl-PHAs) and medium-chain-length polyhydroxyalkanoates (mcl-PHAs) was studied using 2 bacteria, Pseudomonas chlororaphis and Acinetobacter ...lwoffii, which secrete an enzyme, or enzymes, with lipase activity. These bacteria produced clear zones of depolymerization on Petri plates containing colloidal solutions of PHA polymers with different monomer compositions. Lipase activity in these bacteria was measured using p-nitrophenyl octanoate as a substrate. In liquid medium, scl-PHA (e.g., PHBV) and mcl-PHA (e.g., PHO) films were used as the sole carbon source for growth, and after 7 days, 5%–18% loss in mass of PHA films was observed. Scanning electron microscopy of these films revealed bacterial colonization of the polymers, with cracks and pitting in the film surfaces. Degradation of polymers released 3-hydroxyhexanoate, 3-hydroxyoctanoate, and 3-hydroxydecanoate monomers into the liquid medium, depending on the starting polymer. Genes encoding secretory lipases, with amino acid consensus sequences for lipase boxes and oxyanion holes, were identified in the genomes of P. chlororaphis and A. lwoffii. Although amino acid consensus sequences for lipase boxes and oxyanion holes are also present in PHA depolymerases identified in the genomes of other PHA-degrading bacteria, the P. chlororaphis and A. lwoffii lipases had low homology with these depolymerases.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
Pseudomonas chlororaphis PA23 was isolated from soybean roots as a plant-growth-promoting rhizobacterium. This strain secretes a wide range of compounds, including the antibiotics ...phenazine-1-carboxylic acid (PCA), pyrrolnitrin, and 2-hydroxyphenazine. We have determined that P. chlororaphis PA23 can synthesize medium-chain-length polyhydroxyalkanoate (PHA) polymers utilizing free fatty acids, such as octanoic acid and nonanoic acid, as well as vegetable oils as sole carbon sources. Genome analysis identified a pha operon containing 7 genes in P. chlororaphis PA23 that were highly conserved. A nonpigmented strain that does not synthesize PCA, P. chlororaphis PA23-63, was also studied for PHA production. Pseudomonas chlororaphis PA23-63 produced 2.42–5.14 g/L cell biomass and accumulated PHAs from 11.7% to 32.5% cdm when cultured with octanoic acid, nonanoic acid, fresh canola oil, waste canola fryer oil, or biodiesel-derived waste free fatty acids under batch culture conditions. The subunit composition of the PHAs produced from fresh canola oil, waste canola fryer oil, or biodiesel-derived free fatty acids did not differ significantly. Addition of octanoic acid and nonanoic acid to canola oil cultures increased PHA production, but addition of glucose did not. PHA production in the phz mutant, P. chlororaphis PA23-63, was greater than that in the parent strain.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
ABSTRACT
Pseudomonas chlororaphis PA23 is a biocontrol agent that, in addition to producing antifungal compounds, synthesizes polyhydroxyalkanoate (PHA) polymers as a carbon and energy sink. Quorum ...sensing (QS) and the anaerobic regulator (ANR) are required for PA23-mediated fungal suppression; however, the role of these regulators in PHA production is unknown. Strains lacking either QS or ANR accumulated less PHA polymers when propagated on Ramsay's minimal medium (RMM) with glucose or octanoate as the carbon source. In the acyl-homoserine lactone (AHL)-deficient background, all six of the genes in the pha locus (phaC1, phaC2, phaZ, phaD, phaF, phaI) showed reduced expression in RMM glucose, and all except phaC2 were repressed in RMM octanoate. Although changes in gene activity were observed in the anr mutant, they were less pronounced. Analysis of the promoter regions for QS- and ANR-binding consensus sequences revealed putative phzboxes upstream of phaZ and phaI, but no anr boxes were identified. Our findings indicate that altered pha gene expression likely contributes to the lower PHA accumulation in the QS- and ANR-deficient strains, which may be in part indirectly mediated. This study is the first to show that mcl-PHA production is under QS and ANR control.
Changing climate can strongly affect tree growth and forest productivity. The dendrochronological approach to assessing the impact of climate change on tree growth is possible through climate–growth ...correlation analysis. This study uses an individual tree-based approach to model Pinus wallichiana (P. wallichiana) radial growth response to climate across the physiographic gradients in the lower distributional range of Nepal. This study sampled six sites across the Makwanpur district of central Nepal that varied in elevation and aspect, obtaining 180 tree-ring series. Climate data series were obtained from Climate Research Unit (CRU 4.0). The pair correlation approach was used to assess P. wallichiana growth response to climate and site-level physiographic variables such as site-level environmental stress. The study also determined long-term growth trends across the elevation and aspect gradients. Trees at sites with higher elevation and northeast aspect (NEA) were more responsive to winter and spring precipitation, whereas trees with lower elevation and northwest aspect (NWA) were more responsive to winter and spring precipitation. Basal area increment (BAI) analysis showed the variation of growth at site-level environmental stress, suggesting that the sensitivity of forest ecosystems to changing climate will vary across the lower growth limit of P. wallichiana due to differences in local physiographic conditions.
A recombinant of Pseudomonas putida LS461 (deletion of the phaC1phaZphaC2 genes) was constructed by introducing cosmid JC123 carrying a novel phaC116 gene from a metagenomic clone. The resulting ...strain, P. putida LS46123, was able to synthesize polyhydroxyalkanoate (PHA) polymers with novel monomer compositions when cultured on glucose or free fatty acids, and accumulated PHAs from 9.24% to 27.09% of cell dry weight. The PHAs synthesized by P. putida LS46123 contained up to 50 mol % short chain length subunits (3-hydroxybutyrate and 3-hydroxyvalerate), with the remaining monomers consisting of various medium chain length subunits. The PhaC116 protein expressed by P. putida LS46123 had an amino acid sequence similarity of 45% with the PhaC1 protein of the parent strain, P. putida LS46. Predicted 3D structures of the PhaC116 proteins from P. putida LS46123 and P. putida LS46 revealed several differences in the numbers and locations of protein secondary structures. The physical and thermal properties of the novel polymers synthesized by P. putida LS46123 cultured with glucose or free fatty acids differed significantly from those produced by P. putida LS46 grown on the same substrates. PHA polymers with different subunit compositions, and hence different physical and thermal properties, can be tailor-made using novel PHA synthase for specific applications.
Medium chain-length polyhydroxyalkanoates (mcl-PHA) were produced by
LS46 cultured with a variety of carbohydrate and fatty acid substrates. The monomer compositions and molecular weights of the ...polymers varied greatly and was dependent on whether the substrate was metabolized via the fatty acid degradation or the
fatty acid synthesis pathways. The highest molecular weights were obtained from medium chain-length fatty acids, whereas low molecular weights were obtained from longer chain-length and more unsaturated fatty acids or carbohydrates. The differences in monomer compositions and molecular weights due to the choice of substrate did not affect the polymer thermal degradation point. The glass transition temperatures varied from -39.4°C to -52.7°C. The melting points, when observed, ranged from 43.2°C to 51.2°C. However, a profound substrate effect was observed on the crystallinity of these polymers. Reduced crystallinity was observed when the monomer compositions deviated away from C8-C10 monomer lengths. The highest crystallinity was observed from medium chain-length fatty acids, which resulted in polymers with the highest tensile strength. The polymer produced from octanoic acid exhibited the highest tensile strength of 4.3 MPa with an elongation-at-break of 162%, whereas the polymers produced from unsaturated, long-chain fatty acids remained amorphous. A comparative analysis of the substrate effect on the physical-mechanical and thermal properties of mcl-PHAs better clarifies the relationship between the monomer composition and their potential applications, and also aids to direct future PHA synthesis research toward properties of interest.
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