Shift In Molecular Weight Distribution Research Articles

Understanding the Ecological Robustness and Adaptability of the Gut Microbiome in Plastic-Degrading Superworms (Zophobas atratus) in Response to Microplastics and Antibiotics.

Recent discoveries indicate that several insect larvae are capable of ingesting and biodegrading plastics rapidly and symbiotically, but the ecological adaptability of the larval gut microbiome to microplastics (MPs) remains unclear. Here, we described the gut microbiome assemblage and MP biodegradation of superworms (Zophobas atratus larvae) fed MPs of five major petroleum-based polymers (polyethylene, polypropylene, polystyrene, polyvinyl chloride, and polyethylene terephthalate) and antibiotics. The shift of molecular weight distribution, characteristic peaks of C═O, and metabolic intermediates of residual polymers in egested frass proved depolymerization and biodegradation of all MPs tested in the larval intestines, even under antibiotic suppression. Superworms showed a wide adaptation to the digestion of the five polymer MPs. Antibiotic suppression negatively influenced the survival rate and plastic depolymerization patterns. The larval gut microbiomes differed from those fed MPs and antibiotics, indicating that antibiotic supplementation substantially shaped the gut microbiome composition. The larval gut microbiomes fed MPs had higher network complexity and stability than those fed MPs and antibiotics, suggesting that the ecological robustness of the gut microbiomes ensured the functional adaptability of larvae to different MPs. In addition, Mantel's test indicated that the gut microbiome assemblage was obviously related to the polymer type, the plastic degradability, antibiotic stress, and larval survival rate. This finding provided novel insights into the self-adaptation of the gut microbiome of superworms in response to different MPs.

Fragmentation and depolymerization of microplastics in the earthworm gut: A potential for microplastic bioremediation?

The accumulation of microplastics poses potential risks to soil health. Here, we did a preliminary exploration on the potential of Lumbricus terrestris (Oligochaeta) to reduce low-density polyethylene (LDPE), polylactic acid (PLA), and polybutylene adipate terephthalate (PBAT) microplastic (20–648 µm) contamination in soils. The ingestion of microplastics-contaminated soil (1% of microplastics, dw/dw) in a mesocosm system and the ingestion of pure microplastics in the Petri Dish by earthworms were studied. Results show that earthworms survived in the microplastics-contaminated soil (0% mortality in 35 days) but barely when exposed solely to microplastics (30–80% mortality in 4 days). Size-dependent ingestion of microplastics was not observed. The fragmentation of LDPE microplastics in the gizzard facilitated by soil was confirmed by the significantly increased ratio of small-sized (20–113 µm) microplastics from the bulk soil to the gut (from 8.4% to 18.8%). PLA and PBAT microplastics were fragmented by gizzard without the facilitation of soil, the ratios of small-sized (20–113 µm) PLA and PBAT microplastics in the gut were 55.5% and 108.2% higher than in respective pristine distributions. Substantial depolymerization of PLA (weight-average molar mass reduced by 17.7% with shift in molecular weight distribution) and suspected depolymerization of PBAT were observed in the worm gut, while no change in the molar mass was observed for PLA and PBAT microplastics buried in the soil for 49 days. Our results suggest that ingested microplastics could undergo fragmentation and depolymerization (for certain polymers) in the earthworm gut. Further research is needed to reveal the mechanisms of polymer depolymerization in the earthworm gut and to evaluate the feasibility of microplastic bioremediation with earthworms.

Enhanced short-chain fatty acids production through a short-term anaerobic fermentation of waste activated sludge: Synergistic pretreatment of alkali and alkaline hydrolase blend

Short-chain fatty acids (SCFAs) recovery through anaerobic fermentation is a promising pathway to achieve economic benefits and carbon-emission reduction in waste activated sludge management. Although numerous pretreatment approaches have been investigated, alkaline hydrolase blend (AHB) incubation at initial pH 10.0 condition for enhancing anaerobic fermentation has rarely been reported. In this study, the sludge flocs were disintegrated into electronegative particle fragments with extracellular polymeric substance disruption and microbial cell lysis, owing to the synergistic effect of alkali-triggered sludge solubilization and AHB-catalyzed hydrolysis. Substantial sludge hydrolysis and biodegradable organic matter release were thereby induced. After pH 10 + AHB pretreatment for 2 h, numerous SCOD release of 5109 mg/L was achievable, which was approximately 12.4, 2.02, and 1.19 times higher than those in control, pH 10 and pH 10+alkaline protease pretreatments, respectively. Meanwhile, the AHB boosted hydrolysis and biodegradation of dissolved organic matters, promoting a low molecular weight shift in molecular weight distribution. The dissolved organic matter compositions tended to low molecular weight organic matters, accelerating the overall anaerobic fermentation process. Correspondingly, considerable SCFAs of 528.9 mg COD/g VSS was produced through a short-term anaerobic fermentation (3 days), which was 5.6, 1.7 and 1.1 times higher than the maximum SCFAs production by control, pH 10 and pH 12–10+alkaline protease pretreatments, respectively. The produced SCFAs were mostly composed of acetate (58.7%), which could be recovered as biodegradable carbon source. By adopting the AHB-based strategy, economic benefits of 392.4–580.6 CNY/ton sludge SS and carbon-emission reduction of 0.207–0.521 ton CO2/ton sludge SS were achievable. Apparently, the AHB-based strategy is a cost-effective and carbon-beneficial technology for sludge management.

Bacterial conversion of depolymerized Kraft lignin

BackgroundLignin is a potential feedstock for microbial conversion into various chemicals. However, the microbial degradation rate of native or technical lignin is low, and chemical depolymerization is needed to obtain reasonable conversion rates. In the current study, nine bacterial strains belonging to the Pseudomonas and Rhodococcus genera were evaluated for their ability to grow on alkaline-treated softwood lignin as a sole carbon source.ResultsPseudomonas fluorescens DSM 50090 and Rhodococcus opacus DSM1069 showed the best growth of the tested species on plates with lignin. Further evaluation of P. fluorescens and R. opacus was made in liquid cultivations with depolymerized softwood Kraft lignin (DL) at a concentration of 1 g/L. Size-exclusion chromatography (SEC) showed that R. opacus consumed most of the available lower-molecular weight compounds (approximately 0.1–0.4 kDa) in the DL, but the weight distribution of larger fractions was almost unaffected. Importantly, the consumed compounds included guaiacol—one of the main monomers in the DL. SEC analysis of P. fluorescens culture broth, in contrast, did not show a large conversion of low-molecular weight compounds, and guaiacol remained unconsumed. However, a significant shift in molecular weight distribution towards lower average weights was seen after cultivation with P. fluorescens.ConclusionsRhodococcus opacus and P. fluorescens were identified as two potential microbial candidates for the conversion/consumption of base-catalyzed depolymerized lignin, acting on low- and high-molecular weight lignin fragments, respectively. These findings will be of relevance for designing bioconversion of softwood Kraft lignin.

RETRACTED ARTICLE: Bacterial conversion of depolymerized Kraft lignin

BackgroundLignin is a potential feedstock for microbial conversion into various chemicals. However, the degradation rate of native or technical lignin is low, and depolymerization is needed to obtain reasonable conversion rates. In the current study, base-catalyzed depolymerization—using NaOH (5 wt%)—of softwood Kraft lignin was conducted in a continuous-flow reactor system at temperatures in the range 190–240 °C and residence times of 1 or 2 min. The ability of growth of nine bacterial strains belonging to the genera Pseudomonas and Rhodococcus was tested using the alkaline-treated lignin as a sole carbon source.ResultsPseudomonas fluorescens and Rhodococcus opacus showed the best growth of the tested species on plates with lignin. Further evaluation of P. fluorescens and R. opacus was made in liquid cultivations with depolymerized lignin (DL) at a concentration of 1 g/L. Size exclusion chromatography (SEC) showed that R. opacus consumed most of the available lower molecular weight compounds (approximately 0.1–0.4 kDa) in the DL, but the weight distribution of larger fractions was almost unaffected. Importantly, the consumed compounds included guaiacol—one of the main monomers in the DL. SEC analysis of P. fluorescens culture broth, in contrast, did not show a large conversion of low molecular weight compounds, and guaiacol remained unconsumed. However, a significant shift in molecular weight distribution towards lower average weights was seen.ConclusionsRhodococcus opacus and P. fluorescens were identified as two potential microbial candidates for the conversion/consumption of base-catalyzed depolymerized lignin, acting on low and high molecular weight lignin fragments, respectively. These findings will be of relevance for designing bioconversion of softwood Kraft lignin.

Understanding lignin depolymerization to phenols via microwave-assisted solvolysis process

In this study, microwave assisted degradation of lignin, a paper industry and biorefinery waste product, is investigated in presence of different organic solvents such as ethylene glycol (EG), dimethyl sulfoxide (DMSO) and dimethyl formamide (DMF) at different temperatures (100–140°C) and treatment periods (20–80min). Experiments performed in batch microwave reactor revealed that, in all the solvents, a major reduction in weight average molecular weight (Mw) of lignin was observed in the time period of 20–40min. In a polar protic solvent with high loss tangent (EG), maximum reduction in Mw was observed at 120°C, while in polar aprotic solvents (DMSO and DMF), Mw decreased with increase in temperature. Significant yield of phenolics (20wt.%) containing acetosyringone, guaiacol, syringaldehyde, anisole and lignin dimers (m/z 306, 322Da) was obtained at 100°C in DMF and DMSO, while at 140°C, 11wt.% phenolics were obtained in EG. Plausible reactions for the formation of phenolic monomers and dimers include etheric CβO and CαCβ bond cleavages induced by solvent interactions. The shift of molecular weight distribution to higher molecular weights suggested the involvement of recombination reactions at long treatment periods. This study shows that solvent-assisted microwave processing is a promising technique to convert lignin to phenols.

Evaluation of analytical methods for determination of kinetic hydrate inhibitor (KHI) in produced waters

Hydrate inhibitors are one of many field chemicals used in the oil and gas operation to ensure uninterrupted flow of fluids in the pipelines. Thermodynamic inhibitors such as methanol and monoethylene glycol (MEG) are commonly used as field proven products. The use of kinetic hydrate inhibitors (KHIs) is becoming popular due to reduced capital expenditure and operational costs. There is limited information on analytical methodologies for determining KHIs. This paper evaluates the analytical methods for the determination and characterization of a hyperbranched poly (ester amide)-type KHI in the produced water (PW) from oil and gas operations. Methyl orange ion pair extraction and iodine-complexation methods were evaluated as two alternative colorimetric methods for quantitative analysis of the residual KHI in PW generated in one of the Qatari gas fields in the Gulf region. Colorimetric measurements showed that KHI–iodine complexation has two orders of magnitude higher response (response factor 0.02±0.001) than the methyl orange ion-pair extraction method (response factor 0.0005±0.0001). Interferences to the colorimetric methods due to brine matrix, the corrosion inhibitors (CIs), organic components, and sulfide can be minimized for the iodine-complexation method within ±10% relative error with proper dilution of the sample. Size exclusion chromatography (SEC) equipped with refractive index detector (RID) and charged-aerosol detector (CAD) was evaluated as an alternative to the colorimetric methods. The ability of SEC to characterize the shift in molecular weight distribution (MWD) of a selected KHI product that was subject to separation by heated centrifugation was demonstrated. The SEC-RID showed linear response over the range of 0–10 mg/mL KHI while the SEC-CAD was more sensitive with low dynamic range (<1 mg/mL). At present, the SEC can determine KHI in PW semi-quantitatively within 10–20% accuracy with both detectors. The SEC composition of the selected KHI (1.5 wt% in brine matrix) solution showed predominantly mono-modal size distribution in the chloroform extract with an average MW of 2156 Da. The SEC revealed high-molecular-weight fraction (average MW 2993 Da) of KHI was left in the bottom portion of the heated and centrifuged solution leaving the light-molecular-weight size fraction (average MW 1262 Da) in the supernatant. These investigations provide some basis to the KHI analyses in PW.

Structural Characterization of α-Terminal Group of Natural Rubber. 2. Decomposition of Branch-Points by Phospholipase and Chemical Treatments

The treatment of deproteinized natural rubber (DPNR) latex with phospholipases A(2), B, C, and D decreased significantly the long-chain fatty acid ester contents in DPNR and also the molecular weight and Higgins' k' constant, except for phospholipase D treatment. This indicates the presence of phospholipid molecules in NR, which combine rubber molecules together. Transesterification of DPNR resulted in the decomposition of the functional group at the terminal chain-end (alpha-terminal), including phospholipids and formed linear rubber molecules. The addition of small amounts of ethanol into the DPNR solution reduced the molecular weight and shifted the molecular weight distribution (MWD) comparable to that of transesterified DPNR (TE-DPNR). The addition of diammonium hydrogen phosphate into DPNR-latex in order to remove Mg2+ ions yielded a slight decrease in molecular weight and a slight shift in MWD. The phospholipids are expected to link with mono- and diphosphate groups at the alpha-terminal by hydrogen bonding and/or ionic linkages. The decrease in the molecular weight and Huggins' k' constant of DPNR demonstrates the formation of linear molecules after decomposition of branch-points by this treatment, showing that phospholipids participate in the branching formation of NR. The branch-points formed at the alpha-terminus are postulated to originate predominantly by the association of phospholipids via micelle formation of long-chain fatty acid esters and hydrogen bonding between polar headgroups of phospholipids.

Size-exclusion HPLC analysis of epitopes

A size-exclusion chromatography method based on competition between intact antibodies and antigen-binding fragments (Fabs) is used to evaluate relative spatial location of epitopes recognized by monoclonal antibodies. If epitopes are spatially distinct, the presence of a potentially competitive Fab results in formation of complexes of higher molecular weight than those formed by antigen and intact IgG. Complexes of lower molecular weight are formed if the epitopes overlap, are identical, or if, upon formation of the antigen-antibody complex, conformational change occurs that results in loss of epitope. Size-exclusion chromatography of the relevant mixtures reveals these shifts in molecular weight distribution and, therefore, provides an unambiguous determination of spatially independent epitopes. In addition, chromatographic analysis of competition between IgG and its enzymatically prepared Fab is used to evaluate the dissociation rate constant of the antigen-antibody reaction in re-equilibrating mixtures.

Degradation of poly(methyl methacrylate) in CF4 and CF4/O2 plasmas

The degradation of poly(methyl methacrylate) films exposed to CF4 and CF4/O2 plasmas in a parallel plate reactor is investigated by means of gel permeation chromatography. Profile results indicate that degradation is high in the top few thousand angstroms, although reductions in molecular weight are observed throughout the 1.5 μm films. Oxygen additions to CF4 generate increases in PMMA etch rates, but molecular weight profiles suggest that degradation is still confined to the film surface. The shifts in molecular weight distribution obtained from plasma degradation experiments are simulated by a random scissioning model.

The action of somatomedin on glycosaminoglycan synthesis in cultured chick chondrocytes.

A basic somatomedin preparation results in a 2-fold stimulation of incorporation of both [3H]leucine into protein and 35SO4 into glycosaminoglycans by cultured chick sternal chondrocytes. The stimulation is seen in the presence of 20 mM 4-methylumbelliferyl-beta-D-xyloside alone but is not observable in the presence of both xyloside and cycloheximide, indicating that the stimulation by somatomedin is dependent on protein synthesis. Somatomedin stimulates incorporation of leucine into glycosaminoglycans to the same extent to which it stimulates incorporation of sulfate into glycosaminoglycans, suggesting involvement of core protein synthesis. In the presence of the xyloside, however, there is stimulation of synthesis of glycosaminoglycan chains initiated on the xyloside, with a shift in molecular weight distribution to larger molecular weights. Thus, when core protein is not rate limiting, a more general stimulatory effect of somatomedin is observed.

Allyl stearate copolymers and terpolymers: Thermal, mechanical, and solution properties of polymers incorporating vinyl chloride

AbstractPoly(allyl stearate) and selected copolymers and terpolymers modified by allyl stearate were investigated in this work. The systems selected and studied over a wide range of composition, included copolymers with vinyl stearate and with vinyl chloride, and terpolymers containing vinyl chloride and allyl stearate, modified further by vinyl stearate or vinyl acetate. Copolymers of allyl stearate and vinyl stearate were studied incrementally across the range of composition. In the ester copolymers the effect of degradative chain transfer on crystallization and solution properties was studied. A relation was obtained between intrinsic viscosities and number‐average molecular weights; a shift in molecular weight distribution with increase in allyl component was demonstrated. The crystallinity contributed by the side chains was shown to be characterized by isomorphic replacement regardless of molecular weight. Mechanical properties of internally plasticized copolymers of allyl stearate and vinyl chloride, in a limited composition range, were compared with corresponding data for copolymers of vinyl stearate and vinyl chloride. While molecular weight reduction of the allylic copolymers exceeded that for the vinyl ester system, the effect, in the useful plasticization composition range, was not enough to grossly affect ultimate properties. The glass transitions of the hypothetical amorphous homopolymers of both fatty esters were estimated to be the same. Because this Tg was low (ca. −110°C), only relatively small mole fractions of allyl stearate were needed for effective plasticization. Isochronal temperature–composition diagrams also showed both systems to be essentially identical, but marked differences were found for diluent mixtures incorporating di‐2‐ethylhexyl phthalate (DOP). An empirical equation, previously derived, adequately predicted the decline in degree of polymerization with increase in allyl stearate between the limits of the respective homopolymers for all copolymers studied. Terpolymers followed the trends of the copolymers and offered no special property advantage.

EFFECT OF GAMMA RADIATION ON WHEAT PROTEINS

An observed higher degree of autolysis in irradiated (20–200 Krads) wheat is apparently due to increased susceptibility of proteins to protease action. Total amino acid profiles of wheat and of isolated gluten reveal no appreciable changes on irradiation up to 1 Mrad. However, there is an overall increase in free amino acid levels in wheat irradiated at 1 Mrad. Lysine availability in wheat is not affected by radiation treatment. Studies on radiosensitivities of wheat proteins show a shift in molecular weight distribution to lower values.

PROTEIN RELEASE BY BARLEY ALEURONE LAYERS

In addition to releasing hydrolytic enzymes, isolated barley aleurone layers release large amounts of reserve protein. This protein release is only partially dependent on gibberellic acid (GA3). The addition of GA3 causes a shift in molecular weight distribution to lower molecular weight, and a change in the N-terminal profile of the released protein. Inhibition of proteolysis reduces protein release. When proteolysis is inhibited, amylase production can be made partially dependent on added amino acids.