Random Coil Research Articles

Effects of insoluble dietary fiber from mung bean skin on dough and gluten protein properties

Abstract In this study, the influences of the addition of different mung bean skin insoluble dietary fiber (MIDF) contents (0–10 wt%) on the properties of dough and gluten proteins were investigated. With the addition of MIDF, the elastic modulus, viscosity modulus, and loss factor of the dough all showed increasing trends. Additionally, the bound water content significantly increased by 15.37 % (P < 0.05), while the weakly bound water content decreased by 14.32 % (P < 0.05), indicating the migration of weakly bound water to bound water. These changes resulted in increased hardness, chewiness, and gumminess of the dough. Furthermore, the incorporation of MIDF significantly reduced the SS content in gluten by 43.01 % (P < 0.05). Concurrently, the secondary structure of gluten protein transformed from ordered structures, such as α-helices and β-sheets, to disordered structures, such as random coils and β-turns, thereby loosening the protein skeleton structure and affecting the gluten network. These results established a theoretical foundation for the development and enhancement of functional foods enriched with dietary fiber.

Honey induces changes in the molecular structure and microstructure of gluten in wheat-rye sourdoughs.

Chemical oxidizers and redox enzymes have traditionally been used to enhance the quality of baked goods. However, consumers now seek natural and clean-label ingredients, avoiding those with chemical-sounding names. Honey, a natural source of glucose oxidase (GOX), represents a promising alternative to purified enzymes for baking purposes. This study aimed to evaluate the effect of honey on the molecular structure and microstructure of gluten proteins in sourdough fermented by different lactic acid bacteria (LAB) strains. Four wheat-rye (1:1) sourdoughs were prepared, each supplemented with honey and inoculated with a different LAB strain. Additionally, two uninoculated doughs, one with honey (honey dough) and the other without (control dough), were prepared under identical conditions. Electronic paramagnetic resonance spectroscopy revealed the presence of hydrogen peroxide in honey solutions, indicating its role as an active source of GOX. Raman spectroscopy showed that honey addition altered the molecular structure of gluten by increasing the proportion of random coils at the expense of α-helix structures. This change is likely attributed to the competition between honey sugars and gluten proteins for water molecules in this system. Moreover, honey led to a decrease in the free sulfhydryl content of gluten compared to the control dough, suggesting an increase in disulfide crosslinking points. These enhanced protein-protein interactions were observed in scanning electron microscopy micrographs as a coarse gluten network composed of interconnected strands and fibrils. All LAB strains exhibited optimal acidification (pH < 4.3) in honey-supplemented sourdoughs, promoting the hydrolysis of gluten proteins into smaller fragments. Overall, honey-supplemented sourdoughs showed a gradual increase in the β-sheet content while decreasing the proportion of random coils over time. This trend suggests that the polypeptide fragments interacted through interchain hydrogen bonds, leading to a more ordered structure, which likely contributes to providing dough with good baking aptitude.

Effect of cold plasma treatment of sunflower seed protein modification on its structural and functional properties and its mechanism

Sunflower seed protein is a protein rich in amino acids, but its structure is more difficult to be applied due to its poor functional properties. The purpose of this study is to investigate the effect of cold plasma treatment on the structural and functional properties of sunflower seed protein. The results showed that the energetic particles and active substances generated by cold plasma treatment could improve the spatial structure of the protein by bombardment/etching and oxidation, respectively, which led to the change of its secondary structure: α-helices and random coil were transformed to β-sheet and β-turns, and the tertiary structure: the fluorescence intensity was increased, the roughness was decreased, which finally led to the increase of the zeta-potential, the solubility increased to 7.341, and the emulsion increased to 7.341, which led to the increase of the solubility and the fluorescence intensity. to 7.341, and the emulsion activity index and emulsion stability index increased from 1.842 m2/g, 107.5 min to 3.3887 m2/g, 171.4 min. These changes were attributed to the fact that the cold plasma treatment altered the structure of sunflower proteins from tightly hydrophobic to loosely hydrophilic, with the exposure of the internal hydrophobic groups and the protein aggregation from large to small. This provides a theoretical basis for its application in food.

Genome-wide identification, molecular evolution and gene expression of P450 gene family in Cyrtotrachelus buqueti

BackgroundInsect Cytochrome P450 monooxygenase (CYPs or P450s) plays an important role in detoxifying insecticides, causing insect populations to develop resistance. However, the molecular functions of P450 gene family in Cyrtotrachelus buqueti genome are still lacking.ResultsIn this study, 71 CbuP450 genes have been identified. The amino acids length of CbuP450 proteins was between 183 aa ~ 1041 aa. They are proteins with transmembrane domains. The main component of their secondary structure is α-helix and random coils. Phylogenetic analysis showed that C. buqueti and Rhynchophorus ferrugineus were the most closely related. This gene family has 29 high-frequency codons, which tend to use A/T bases and A/T ending codons. Gene expression analysis showed that CbuP450_23 in the female adult may play an important role on high temperature resistance, and CbuP450_17 in the larval may play an important role on low temperature tolerance. CbuP450_10, CbuP450_17, CbuP450_23, CbuP450_10, CbuP450_16, CbuP450_20, CbuP450_23 and CbuP450_ 29 may be related to the regulation of bamboo fiber degradation genes in C. buqueti. Protein interaction analysis indicates that most CbuP450 proteins are mainly divided into three aspects: encoding the biosynthesis of ecdysteroids, participating in the decomposition of synthetic insecticides, metabolizing insect hormones, and participating in the detoxification of compounds.ConclusionsWe systematically analyzed the gene and protein characteristics, gene expression, and protein interactions of CbuP450 gene family, revealing the key genes involved in the stress response of CbuP450 gene family in the resistance of C. buqueti to high or low temperature stress, and identified the key CbuP450 proteins involved in important life activity metabolism. These results provided a reference for further research on the function of P450 gene family in C. buqueti.

Using Poly(N‐isopropylacrylamide) and Poly(ethyleneglycol) Grafted Polycarbodiimides as Unique Nanocarriers for Hydrophobic Form of the Doxorubicin (DOX)

Using Poly(<i>N</i>‐isopropylacrylamide) and Poly(ethyleneglycol) Grafted Polycarbodiimides as Unique Nanocarriers for Hydrophobic Form of the Doxorubicin (<scp>DOX</scp>)

Impact of pH-mediated in situ enzymatic pretreatment on food waste decomposition and biomethane production: Performance, mechanism, and key metabolic pathways

pH value universally presents the great influence on hydrolysis efficiency of food waste (FW) by in situ enzymatic pretreatment, while the influencing mechanism of pH value on enzymatic decomposition of FW is not clear at present. This study innovatively in situ prepared a microbial-based compound enzyme (MCE) from FW, as well as systematically deciphered the impact and underlying mechanism of pH-mediated MCE pretreatment on FW decomposition and biomethane production. The dissolution, biodegradability and monomer formation of FW were found to be promoted by MCE pretreatment, and the highest hydrolysis efficiency was obtained at pH 5, while the biomethane yield was accordingly increased by 30.89 % compared to the control. The dissection of Fourier transform infrared spectroscopy (FTIR) results unraveled that the reaction order of FW components was protein → lipid → starch → cellulose in the acid-enhanced process, while the order shifted to starch → protein → cellulose → lipid in the alkali-enhanced process. Moreover, the looser protein structure was obtained after MCE pretreatment due to α-helix/(β-sheet + random coil) value was declined from 60.35 % to 57.01 %-49.03 %. These changes induced by pH-mediated MCE pretreatment reshaped the bacterial microbial community in favor of biomethane production, and the metagenomic analysis further demonstrated that MCE pretreatment had the highest abundances of genes related to metabolic functions of level 2 and 3 at pH 5, while the abundances of over 90 % key enzyme-encoding genes associated with hydrolysis, acidogenesis and methanogenesis were also increased during the anaerobic digestion process, therefore harvesting the highest biomethane yield.

Impact of pilot-scale microfluidization on soybean protein structure in powder and solution

The effect of microfluidization treatment on the primary, secondary, and tertiary structure of soybean protein isolate (SPI) was investigated. The samples were treated with and without controlling the temperature and circulated in the system 1, 3, and 5 times at high pressure (137 MPa). Then, the treated samples were freeze-dried and reconstituted in water to check the impact of the microfluidization on two different states: powder and solution. Regarding the primary structure, the SDS-PAGE analysis under reducing conditions showed that the protein bands remained unchanged when exposed to microfluidization treatment. When the temperature was controlled for the samples in their powder state, a significant decrease in the quantities of β-sheet and random coil and a slight reduction in α-helix content was noticed. The observed decrease in β-sheet and the increase in β-turns in treated samples indicated that microfluidization may lead to protein unfolding, opening the hydrophobic regions. Additionally, a lower amount of α-helix suggests a higher protein flexibility. After reconstitution in water, a significant difference was observed only in α-helix, β-sheet and β-turn. Related to the tertiary structure, microfluidization increases the surface hydrophobicity. Among all the conditions tested, the samples where the temperature is controlled seem the most suitable.

3D-MPEA: A Graph Attention Model-Guided Computational Approach for Annotating Unknown Metabolites in Interactomics via Mass Spectrometry-Focused Multilayer Molecular Networking.

The spectral matching strategy of MS2 fragment spectrograms serves as a ubiquitous method for compound characterization within the matrix. Nevertheless, challenges arise due to the deficiency of distinctions in spectra across instruments caused by coelution peak-derived fragments and incompleteness of the current spectral reference database, leading to dilemma of multidimensional omics annotation. The graph attention model embedded with long short-term memory was proposed as an optimized approach involving integrating similar MS2 spectra into molecular networks according to the isotopic ion peak cluster spacing features to collapse diverse ion species and expand the spectral reference library, which efficiently evaluated the substance capture capacity to 123.1% than classic substance perception tactics. The versatility and utility of the established annotation procedure were showcased in a study on the stimulation of pork mediated by 2,2-bis(4-hydroxyphenyl)propane and enabled the global metabolite annotation from knowns to unknowns at metabolite-lipid-protein level. On the spectra for which in silico extended spectral library search provided a group truth, 83.5-117.1% accuracy surpassed 1.2-14.3% precision after manual validation. β-Ala-His dipeptidase was first evidenced as the critical node related to the transformation of α-helical (36.57 to 35.74%) to random coil (41.53 to 42.36%) mediated by 2,2-bis(4-hydroxyphenyl)propane, ultimately triggering an augment of catalytic performance, inducing a series of oxidative stress, and further intervening in the availability of animal-derived substrates. The integration of ionic fragment feature networks and long short-term memory models allows the effective annotation of recurrent unknowns in organisms and the deciphering of unacquainted matter in multiomics.

Transglutaminase-crosslinked cold-set pea protein isolate gels modified by pH shifting: Properties, structure and formation mechanisms

The poor gelation properties of pea protein isolate (PPI) limit their use in food industries. In the present study, PPI was modified by pH-shifting combined with heat treatment, followed by cold-set gelation of PPI gels induced by transglutaminase. Both pH 2–3 and pH 10–12 promoted the unfolding of PPI molecules and the transformation of secondary structures from ordered to disordered. In particular, PPI molecules with pH 12-shifting tended to expand and unfold, which resulted in the exposure of internal active groups and improvement in surface hydrophobicity. Accordingly, after the addition of 50 U/g transglutaminase, PPI gels with pH 12-shifting and heating treatment exhibited homogeneous and dense gel network with high cross-linking degree (88.12 ± 1.80%) and water holding capacity (92.13 ± 2.40%), since pH 12-shifting and heating treatment promoted the conversion of random coils and β-turns to β-folds and α-helices in PPI gels. However, with pH 10 and 11-shifting, the PPI molecules was partially unfolded and the PPI gels had a high non-network protein content, resulting in low-strength gel networks of PPI gels with rough and loose microstructures and a low WHC. These results showed that TGase-crosslinked cold-set PPI gels after pH 12-shifting and heat treatment could promote the formation of homogeneous and dense gel network structure, so that improved the PPI gelation properties, which had great potential to be used as gelling agents or nutraceutical delivery systems for thermal sensitive bioactive compounds in food and non-food fields.

Cloning and Bioinformatics Analysis of FecB Gene in Improved Offspring of Suffolk Sheep

As is well known, the FecB (BMPR-IB) gene, as the earliest gene discovered by scientists that is closely related to sheep fertility, is the major gene responsible for multiple births in sheep. FecB gene shows a notable linkage with the quantity of newborn lambs. However, there has been limited research on the physicochemical properties and distribution of FecB in the improved descendants of Suffolk sheep. Therefore, this study first constructed a phylogenetic tree of the FecB (BMPR1B) protein in 30 species. The results showed that the improved descendants of Suffolk sheep are closely related to goats, water buffalo, domestic cattle, and humped cattle, indicating a strong level of conservation of BMPR-IB gene within the genus. At the same time, the physicochemical properties and structure of the FecB protein were analyzed, revealing that the FecB protein in the improved descendants of Suffolk sheep is positively charged, belongs to hydrophilic unstable alkaline proteins, contains a signal peptide, is a transmembrane protein, and has 56 phosphorylation sites. The secondary structure of the FecB protein consists of α-helices, extended chains, β-turns, and random coils, accounting for 34.86%, 13.15%, 3.39%, and 48.61%, respectively. Protein interaction analysis also showed that FecB has extensive regulatory interactions with members of the bone morphogenetic protein family. However, the examination of the BMPR-IB gene’s expression levels in nine tissues, which encompasses the heart, liver, spleen, and ovaries of the improved descendants of Suffolk sheep, showed the highest expression in the kidneys and the lowest expression in the spleen and small intestine. This study extensively explored the tissue expression profile and protein physicochemical structure of the BMPR-IB gene in the improved descendants of Suffolk sheep, aiming to lay a theoretical foundation for selecting high-yield improved descendants of Suffolk sheep.

Structural and biochemical characterization of the mitomycin C repair exonuclease MrfB.

Mitomycin C (MMC) repair factor A (mrfA) and factor B (mrfB), encode a conserved helicase and exonuclease that repair DNA damage in the soil-dwelling bacterium Bacillus subtilis. Here we have focused on the characterization of MrfB, a DEDDh exonuclease in the DnaQ superfamily. We solved the structure of the exonuclease core of MrfB to a resolution of 2.1 Å, in what appears to be an inactive state. In this conformation, a predicted α-helix containing the catalytic DEDDh residue Asp172 adopts a random coil, which moves Asp172 away from the active site and results in the occupancy of only one of the two catalytic Mg2+ ions. We propose that MrfB resides in this inactive state until it interacts with DNA to become activated. By comparing our structure to an AlphaFold prediction as well as other DnaQ-family structures, we located residues hypothesized to be important for exonuclease function. Using exonuclease assays we show that MrfB is a Mg2+-dependent 3'-5' DNA exonuclease. We show that Leu113 aids in coordinating the 3' end of the DNA substrate, and that a basic loop is important for substrate binding. This work provides insight into the function of a recently discovered bacterial exonuclease important for the repair of MMC-induced DNA adducts.

Conformation-Activity Mechanism of Alcalase Hydrolysis for Reducing In Vitro Allergenicity of Instant Soy Milk Powder.

Effective reduction of the allergenicity of instant soy milk powder (ISMP) is practically valuable for expanding its applications. This study optimized the enzymolysis technology of ISMP using single-factor experiments and response surface methodology, combined serological analysis, cellular immunological models, bioinformatics tools, and multiple spectroscopy techniques to investigate the effects of alcalase hydrolysis on allergenicity, spatial conformation, and linear epitopes of ISMP. Under the optimal process, special IgE and IgG1 binding abilities and allergenic activity to induce cell degranulation of alcalase-hydrolyzed ISMP were reduced by (64.72 ± 1.76)%, (56.79 ± 3.72)%, and (73.3 ± 1.19)%, respectively (P < 0.05). Moreover, the spatial conformation of instant soy milk powder hydrolysates (ISMPH) changed, including decreased surface hydrophobicity, a weaker peak of amide II band, lower contents of α-helix and β-sheet, and an enhanced content of random coil. Furthermore, the linear epitopes of major soy allergens, 9 from glycinin and 13 from β-conglycinin, could be directionally disrupted by alcalase hydrolysis. Overall, the structure-activity mechanism of alcalase hydrolysis to reduce ISMP allergenicity in vitro was preliminarily clarified. It provided a new research direction for the breakthrough in the desensitization of ISMP and a theoretical basis for revealing the potential mechanism of alcalase enzymolysis to reduce the allergenicity of ISMP.

Effects of ultrasound on the structural, physicochemical, and emulsifying properties of aquafaba extracted from various legumes

This study investigated the effect of ultrasound (20–60 min, 40 kHz, 280 W) on the structural, physicochemical, and emulsifying properties of aquafaba extracted from various legumes (chickpea [CH], yellow soybean [YSB], black soybean [BSB], small black bean [SBB]). The hydrophobic amino acids and protein secondary structures (α-helix, random coil) significantly increased with sonication time (p < 0.05). The particle size of aquafaba was reduced by ultrasound (p < 0.05). A total of 27 volatile compounds were identified. Most volatiles increased with sonication time, and beany flavor was lowest in CH and SBB. The EAI, ESI, adsorbed proteins, and zeta-potential increased, while emulsion droplet size decreased in all legumes by ultrasound. The overall emulsifying properties were the highest in SBB sonicated for 40 min. This study discusses the applicability of ultrasound to aquafaba and provides insights into the functional properties and potential of aquafaba as a plant-based natural emulsifier

Fluctuation of flavor quality in roasted duck: The consequences of raw duck preform’s repetitive freeze-thawing

This study aimed to investigate the changes in flavor quality of roasted duck during repetitive freeze-thawing (FT, −20 ℃ for 24 h, then at 4 ℃ for 24 h for five cycles) of raw duck preforms. HS-SPME/GC–MS analysis showed that more than thirty volatile flavor compounds identified in roasted ducks fluctuated with freeze-thawing of raw duck preforms, while hexanal, nonanal, 1-octen-3-ol, and acetone could as potential flavor markers. Compared with the unfrozen raw duck preforms (FT-0), repetitive freeze-thawing increased the protein/lipid oxidation and cross-linking of raw duck preforms by maintaining the higher carbonyl contents (1.40 ∼ 3.30 nmol/mg), 2-thiobarbituric acid reactive substances (0.25 ∼ 0.51 mg/kg), schiff bases and disulfide bond (19.65 ∼ 30.65 μmol/g), but lower total sulfhydryl (73.37 ∼ 88.94 μmol/g) and tryptophan fluorescence intensity. Moreover, A lower protein band intensity and a transformation from α-helixes to β-sheets and random coils were observed in FT-3 ∼ FT-5. The obtained results indicated that multiple freeze-thawing (more than two cycles) of raw duck preforms could be detrimental to the flavor quality of the roasted duck due to excessive oxidation and degradation.

The influence of the interaction between whey protein and erythritol on protein conformation, interfacial properties and stability

This study investigated the impact of erythritol (ERY) on structural and functional properties of whey protein isolate (WPI). FTIR and CD revealed that WPI underwent structural changes, including formation of β‐folds and random coils, upon interaction with 20 mg/mL ERY. SEM showed increased surface roughness of WPI, indicating enhanced protein exposure. Moreover, binding rate exceeded 85%, accompanied by increased surface hydrophobicity. Fluorescence spectroscopy indicated a red shift in fluorescence of WPI and tyrosine (Tyr) residues, altering polarity of Tyr environment due to ERY coordination. Additionally, ERY presence enhanced the functional properties of WPI, including foaming, freeze–thaw stability, rheology and antioxidant activity.

Impact of roasted oat flour on the gas cell structure of steamed oat cake and its underlying mechanism

Roasting (or called stir-frying) can modify the properties of oat flour and improve the poor quality of steamed oat cake, especially uneven gas cell and high hardness, but the underlying mechanism remains unclear. The properties of protein-starch network matrix of oat dough (made by roasted oat flours with gelatinization degrees of 30%, 50% 70% and 90%) before and after steaming were investigated, as well as the air/water interfacial characteristics of oat dough liquor. Results revealed that adding roasted oat flour with moderate gelatinization degree to the raw oat flour (ROF) could significantly improve the quality of steamed oat cakes, and their average pore size and specific volume reached the corresponded maximum values when roasted oat flour with gelatinization degree of 50% (G50) was added, which were 1.97 mm and 2.56 mL/g, respectively. Roasted oat flour with moderately gelatinization could not only facilitate the formation of protein polymers by promoting disulfide cross-linking of larger monomer proteins in both raw and steamed oat dough, but also induce the conversion of random coil to α-helix and β-sheets structure, resulting in an ordered protein secondary structure. Meanwhile, the improvement of short-range molecular order structure of starch in oat dough was observed for ROF/G50（w/w = 1:1）sample (RG50). Additionally, compared to ROF, RG50 sample possessed the strongest foaming stability, which increased from 32.70% to 61.43%. In conclusion, the quality enhancement of steamed oat cake can be attributed to the combined effects of changes in the protein-starch matrix and the thin liquid film induced by moderately roasted oat flour.

Including the Ensemble of Unstructured Conformations in the Analysis of Protein's Native State by High-Pressure NMR Spectroscopy.

The analysis of pressure induced changes in the chemical shift of proteins allows statements on structural fluctuations proteins exhibit at ambient pressure. The inherent issue of separating general pressure effects from structural related effects on the pressure dependence of chemical shifts has so far been addressed by considering the characteristics of random coil peptides on increasing pressure. In this work, chemically and pressure denatured states of the cold shock protein B from Bacillus subtilis (BsCspB) have been assigned in 2D 1H-15N HSQC NMR spectra and their dependence on increasing hydrostatic pressure has been evaluated. The pressure denatured polypeptide chain has been used to separate general from structural related effects on 1H and 15N chemical shifts of native BsCspB and the implications on the interpretation of pressure induced changes in the chemical shift regarding the structure of BsCspB are discussed. It has been found that the ensemble of unstructured conformations of BsCspB shows different responses to increasing pressure than random coil peptides do. Thus, the approach used for considering the general effects that arise when hydrostatic pressure increases changes the structural conclusions that are drawn from high pressure NMR spectroscopic experiments that rely on the analysis of chemical shifts.

Including the Ensemble of Unstructured Conformations in the Analysis of Protein's Native State by High‐Pressure NMR Spectroscopy

The analysis of pressure induced changes in the chemical shift of proteins allows statements on structural fluctuations proteins exhibit at ambient pressure. The inherent issue of separating general pressure effects from structural related effects on the pressure dependence of chemical shifts has so far been addressed by considering the characteristics of random coil peptides on increasing pressure. In this work, chemically and pressure denatured states of the cold shock protein B from Bacillus subtilis (BsCspB) have been assigned in 2D 1H‐15N HSQC NMR spectra and their dependence on increasing hydrostatic pressure has been evaluated. The pressure denatured polypeptide chain has been used to separate general from structural related effects on 1H and 15N chemical shifts of native BsCspB and the implications on the interpretation of pressure induced changes in the chemical shift regarding the structure of BsCspB are discussed. It has been found that the ensemble of unstructured conformations of BsCspB shows different responses to increasing pressure than random coil peptides do. Thus, the approach used for considering the general effects that arise when hydrostatic pressure increases changes the structural conclusions that are drawn from high pressure NMR spectroscopic experiments that rely on the analysis of chemical shifts.

Structural characteristics of organics released from sludge pretreatment and their performance in the synthesis of biomass plastics

The conversion of organics from sludge into high-value added products is essential for achieving circular economy and sustainable development in wastewater treatment processes. Currently, research focuses on promoting the release of organics from sludge, but there is a lack of in-depth understanding of the properties and structures of the released organics. To find out a suitable sludge pretreatment method (ultrasound, alkaline, thermal, ultrasound-alkaline, alkaline-thermal hydrolysis) for biodegradable plastic synthesis, the composition, properties and structures of the released organics from sludge were studied. Alkaline treatment (pH 12) resulted in the highest surface charge with Zeta potential of –23.53 mV. The release concentration and the radius of rotation (17.79 nm) of proteins were maximized after pH 12 + 150 °C pretreatment. Ultrasound treatment disrupted the extracellular polymeric substances of sludge, releasing organics with the highest thermal stability and hydrophobicity indices (20,313). Simultaneously, β-sheets was the main secondary structure of proteins. Random coils were the main proteins secondary structure after the other pretreatments instead. Meanwhile, small-angle scattering calculations showed that the released proteins tended to be discoidal for all pretreatment methods. In addition to proteins, polysaccharides, and humic acids, small organic compounds were also produced, such as amino acids (D-alanine), aromatic compounds (pyridine), alcohols, sugars (pyranose), fatty acids (oleic and palmitic), small molecule acids (acetic), etc. Furthermore, pretreatment with pH 12 + 150 °C was more efficient for the whole process of sludge synthesis into plastics. Correlation analysis shows that the radius of rotation of proteins is the main factor affecting the tensile strength and elongation at break of synthetic plastics. This study conducted an in-depth analysis of the structure and properties of organics after different pretreatments and provided a new pathway for the resource utilization of sludge through the synthesis of plastics using sludge organics.

The combination of ciprofloxacin and dialkyldimethyl ammonium compound synergistically proliferated intracellular resistance genes in nitrifying system

Antibiotics and quaternary ammonium compounds (QACs) usually co-exist in wastewater treatment plants. Hence, three sequencing batch reactors were established and named as R1, R2 and R3, to investigate the effects of individual and combined exposure of different concentrations of ciprofloxacin (CIP) (0.2, 1.0 and 2.0 mg/L) and dialkyldimethyl ammonium compound (DADMAC) (0.4, 2.0 and 4.0 mg/L) on the performance, microbial community structures and resistance genes (RGs) in nitrifying system during 150 days. Results showed that CIP had a slight effect on ammonia oxidation activity, while 2.0 and 4.0 mg/L DADAMAC could obviously inhibit it, and the combination of CIP and DADMAC had a synergistic inhibitory effect. Besides, both CIP and DADMAC caused partial nitrification, and the order of nitrite accumulation rate was ranked as R3 > R2 > R1. The combination of CIP and DADMAC had an antagonistic effect on the increase of sludge particle size and α-Helix/(β-Sheet + Random coil) was lowest in R3 (0.40). The combination of CIP and DADMAC synergistically stimulated most intracellular RGs in sludge, and the relative abundances of target RGs (e.g., qacEdelta1-01, qacH-01 and qnrS) at the end of operation in R3 were increased by 4.61–18.19 folds compared with those in CK, which were 1.34–5.57 folds higher than the R1 and R2. Moreover, the combination of CIP and DADMAC also promoted the transfer of RGs from sludge to water and enriched more potential hosts of RGs, further promoting the spread of RGs in nitrifying system. Thus, the combined pollution of CIP and DADMAC in wastewaters should attract more attentions.