Exploring the potential of iTRAQ proteomics for tracking the transformation of extracellular proteins from enzyme-disintegrated waste activated sludge

Revealing extracellular protein profile and excavating spoilage-related proteases of Aeromonas salmonicida based on multi-omics investigation

Aeromonas is a ubiquitous aquatic bacteria, and it is a significant factor contributing to meat spoilage during processing and consumption. The abilities of Aeromonas salmonicida 29 and 57, which exhibit spoilage heterogeneity, to secrete protease, lipase, hemolysin, gelatinase, amylase, and lecithinase were confirmed by plate method. A total of 3948 proteins were identified by ITRAQ in extracellular secretions of A. salmonicida, and 16 proteases were found to be potentially related to spoilage ability. The complete genome sequence of A. salmonicida 57 consists of one circular chromosome and three plasmids, while A. salmonicida 29 consists of one circular chromosome, without a plasmid. Transcriptomic analysis revealed a significant number of DEGs were up-regulated in A. salmonicida 29, which were mainly enriched in metabolic pathways (e.g., amino acid metabolism, carbohydrate metabolism), indicating that A. salmonicida 29 had better potential to decompose and utilize nutrients in meat. Six protease genes (2 pepB, hap, pepA, ftsI, and pepD) were excavated by combined ITRAQ with transcriptome analysis, which potentially contribute to bacterial spoilage ability and exhibit universality among other dominant spoilage bacteria. This investigation provides new insights and evidence for elucidating metabolic and spoilage phenotypic differences and provides candidate genes and strategies for future prevention and control technology development.

Response surface optimization of sludge dewatering process: synergistic enhancement by ultrasonic, chitosan and sludge-based biochar

Due to the colloidal stability, the high compressibility and the high hydration of extracellular polymeric substances (EPS), it is difficult to efficiently dehydrate sludge. In order to enhance sludge dewatering, the process of ultrasonic (US) cracking, chitosan (CTS) re-flocculation and sludge-based biochar (SBB) skeleton adsorption of water-holding substances to regulate sludge dewaterability was proposed. Based on the response surface method, the prediction model of the specific resistance to filtration (SRF) and sludge cake moisture content (MC) was established. The US cracking time and the dosage of CTS and SBB were optimized. The results showed that the optimal parameters of the three were 5.08 s, 10.1 mg/g dry solids (DS) and 0.477 g/g DS, respectively. Meantime, the SRF and MC were 5.4125 × 1011 m/kg and 76.8123%, which significantly improved the sludge dewaterability. According to the variance analysis, it is found that the fitting degree of SRF and MC model is good, which also confirms that there is significant interaction and synergy between US, CTS and SBB, and the contribution of CTS and SBB is greater. Moreover, the process significantly improves the sludge's calorific value and makes its combustion more durable.

Multi-omics reveals aspirin eugenol ester alleviates neurological disease

BACKGROUND

Exosomes play an essential role in maintaining normal brain function due to their ability to cross the blood-brain barrier. Aspirin eugenol ester (AEE) is a new medicinal compound synthesized by the esterification of aspirin with eugenol using the prodrug principle. Aspirin has been reported to have neuroprotective effects and may be effective against neurodegenerative diseases.

PURPOSE

This study wanted to investigate how AEE affected neurological diseases in vivo and in vitro.

EXPERIMENTAL APPROACH

A multi-omics approach was used to explore the effects of AEE on the nervous system. Gene and protein expression changes of BDNF and NEFM in SY5Y cells after AEE treatment were detected using RT-qPCR and Western Blot.

KEY RESULTS

The multi-omics results showed that AEE could regulate neuronal synapses, neuronal axons, neuronal migration, and neuropeptide signaling by affecting transport, inflammatory response, and regulating apoptosis. Exosomes secreted by AEE-treated Caco-2 cells could promote the growth of neurofilaments in SY5Y cells and increased the expression of BDNF and NEFM proteins in SY5Y cells. miRNAs in the exosomes of AEE-treated Caco-2 cells may play an important role in the activation of SY5Y neuronal cells.

CONCLUSIONS

In conclusion, AEE could play positive effects on neurological-related diseases.

New insights into mycelial pellets for aerobic sludge granulation in membrane bioreactor: Bio-functional interactions among metazoans, microbial communities and protein expression

Direct cultivation of aerobic granular sludge (AGS) in membrane bioreactor (MBR) has gained increasing attention. Mycelial pellets (MPs) has been shown capable of promoting rapid granulation of aerobic sludge in MBR, yet mechanisms remain unclear and in-depth insight into cross-scale interactions between MPs and indigenous microbiota as well as the corresponding protein expression functions is necessary. Herein, we found that the addition of MPs in MBR resulted in massive growth of metazoans with 40-400 /mL for rotifers, 20-140 /mL for nematodes and 2-420 /mL for oligochaetes in the initial phase of granulation. This facilitated the MPs to rapidly aggregate with bacteria to form defensive granules for physical protection from predation by metazoans, which inhibited the overgrowth of filamentous bacteria Thiothrix and promoted the reproduction of functional bacteria related to nitrogen removal (Nitrospira, Trichococcus and Acinetobacter). Proteomic analysis demonstrated that the upregulation of functional proteins was mainly ascribed to the decrease of Thiothrix and the increase of Nitrospira, resulting in the enhancement of metabolic pathways involved in glycolysis/gluconeogenesis, citrate (TCA) cycle, oxidative phosphorylation, pyruvate metabolism, nitrogen metabolism and biosynthesis of amino acids, which was responsible for MPs-induced AGS with denser structure, more abundant proteins and β-polysaccharides, higher species diversity, significant nitrogen removal (33.12-42.33%) and lower membrane fouling potential. This study provided a novel and comprehensive insight into the enhanced granulation of aerobic sludge by MPs and the functional superiority of MPs-induced AGS in MBR system.

A novel application of dissolved ozone flotation on sewage sludge thickening: Performance and mechanism investigation

Sludge thickening in sewage treatment plants is an essential step to reduce the sewage sludge volume and provide space for collaborative anaerobic digestion of sludge and other urban organic wastes. Dissolved ozone flotation (DOF) is a novel choice worthy of application in the field of sludge thickening. In order to investigate the effect of DOF thickening, the total solid content (TS %) was used to characterize the thickening performance under different O₃ dosage. The optimal condition was determined to be polyacrylamide (PAM) dosage = 3 ‰ TS, air floatation time = 2 h and O₃ dosage = 12 mg/g TS, under which the TS % of raw-sewage sludge (RS) increased from 0.33 ± 0.01 % to 8.03 ± 0.06 %. In this study, the relationship between the sludge thickening performance, physicochemical properties, and the changes of organic matter (content, structure and molecular weight) in extracellular polymers (EPS) was systematically clarified. The results indicated that the DOF couple with PAM could change the sludge surface properties, destroy the sludge floc structure, release intracellular organic matter, and increase moisture fluidity. The surface hydrophilicity/hydrophobicity, protein (PN) secondary structure and moisture distribution were mainly responsible for sludge thickening performance. Moreover, the change of TS % during the DOF thickening process was mainly caused by the variations of the organic matter content in EMPS layer. The identification of key influencing factors was conducive to the further regulation and upgrading of the novel application for enhanced sludge thickening in sewage treatment plants.

Differential proteomic analysis of citrus flavor (+)-valencene biotransformation to (+)-nootkatone by Yarrowia lipolytica

Natural products (+)-nootkatone is an important sesquiterpene compound and is widely used in pharmaceutical, cosmetic, agricultural and food industries. The aim of this study was to analyze the differentially expressed proteins (DEPs) during citrus aroma compound (+)-valencene biotransformation to (+)-nootkatone by Yarrowia lipolyticaby with high-throughput LC-MS/MS. A total of 778 proteins were differentially expressed, 385 DEPs were significantly up-regulated and 393 DEPs were markedly down-regulated. It was found that the enzymes transformed (+)-valencene to (+)-nootkatone were mainly existed in yeast intracellular and precipitated under the condition of 30-40 % ammonium sulfate. Most DEPs involved in amino acid and fatty acid metabolism were down-regulated during (+)-valencene biotransformation. The DEPs related to the carbohydrate metabolism, energy metabolism and most of transporter proteins were significantly up-regulated. Furthermore, the key enzymes involved in (+)-valencene transformation might be related to cytochrome P450s (gene2215 and gene2911) and dehydrogenases (gene6493). This is the first time that proteomics was used to investigate the metabolism mechanism of Yarrowia lipolytica during (+)-valencene biotransformation. The proteomic analysis of Yarrowia lipolytica provided a foundation for the molecular regulatory mechanism in the biotransformation to (+)-nootkatone from (+)-valencene.

Performance and mechanism of sulfamethoxazole removal in different bioelectrochemical technology-integrated constructed wetlands

Sulfamethoxazole (SMX) has a high concentration and detection frequency in aquatic environments due to the poor removal efficiency of traditional biological treatment processes. Bioelectrochemical technology-integrated constructed wetlands (CWs) have great potential for SMX removal; however, the process of SMX removal in different bioelectrochemical technology-integrated CWs (microbial fuel cell (MFC) and direct current (EC)) remains unclear. To address this, we examined the mechanism of SMX removal in MFCCW and ECCW. The results revealed that the SMX removal efficiency can reach 96.0 ± 2.4% in the ECCW and 97.2 ± 2.2% in the MFCCW. The enhancement of MFC for SMX removal in CW was slightly better than that in direct current (p > 0.05). It was found that the adsorption process of SMX in the substrate promoted by EC was more enhanced than that by MFC. Furthermore, bioelectrochemical technology improved plant activity, including root and enzymatic (superoxide dismutase, peroxidase, and catalase) activities, and fluorescence parameters (photochemical quenching coefficient, non-photochemical quenching coefficient, and quantum efficiency of PS II). Significant differences were found between CW and ECCW (p < 0.05), while no significant differences were found between CW and MFCCW (p > 0.05). The microbial activity and abundance in CW were improved by bioelectrochemical technology, and the microbial community structure was optimised to be simpler and more stable. However, EC tended to promote microbial and plant activity in CW, whereas MFC tended to optimise the microbial community and improve the tightness and stability of the module. The enhanced difference might also account for the changes in the SMX degradation pathway. 4-aminobenzenesulfonic acid (TP174), 3-amino-5-methylisoxazole (TP99) and 5-methylisoxazole (TP84) were all common products in the three reactors, whereas TP99 underwent further ring-opening in MFCCW and TP174 underwent further hydrolysis in ECCW. This study provided an important reference for the targeted regulation of plants and microorganisms in constructed wetlands via different bioelectrochemistry to enhance characteristic pollutants degradation.

Response of extracellular polymeric substances and microbial community structures on resistance genes expression in wastewater treatment containing copper oxide nanoparticles and humic acid

The extracellular polymeric substances (EPS) and microbial community structures were investigated in wastewater treatment containing copper oxide nanoparticles (CuO NPs) (reactor R1) and CuO NPs and humic acid (HA) (reactor R2) using both sequencing batch bioreactors (SBRs), and their response on resistance genes expression was analyzed. The removal of influent chemical oxygen demands (COD) and NH₄⁺-N was moderately influenced under CuO NPs (5 mg/L) stress, while the function of HA (10 mg/L) was not reflected. However, the EPS production and microbial community were affected by the HA addition. The expression of different antibiotic resistance genes (ARGs), metal-resistance genes (MRGs), and intI1 was related to the primary compositions of polysaccharides and proteins in EPS and different microbial communities at the genus level. Furthermore, the expression of resistance genes was not stimulated under CuO NPs stress, and supplying HA was suggested to reduce their expression in wastewater treatment.

Irbesartan ameliorates chronic mountain sickness in a rat model via the cholesterol metabolism: An iTRAQ -based proteomics analysis

OBJECTIVE

To study the effects of irbesartan on pulmonary artery lesions in a rat model with chronic mountain sickness (CMS) and identify the biomarkers involved.

METHODS

In this study, we used a rat model of CMS to evaluate the therapeutic effect of irbesartan by measuring pulmonary artery pressure and evaluating the histopathology of the pulmonary artery. We also used proteomics technology to identify differentially expressed proteins (DEPs) in the serum and performed bioinformatics analysis. Results were then verified by enzyme linked immunosorbent assay (ELISA) and immunohistochemistry (IHC).

RESULTS

Irbesartan treatment induced a significant decrease (P < 0.05) in the pulmonary artery pressure of CMS rats. Histopathological and electron microscope further confirmed that high altitude hypoxia induced changes in the structure of the pulmonary artery tissue and caused ultrastructural lesions. Proteomics analysis identified 40 DEPs; bioinformatics analysis further revealed that the cholesterol metabolism pathway plays a crucial role in the occurrence of CMS. ELISA and IHC verified that several DEPs (Apo-A1, Apo-C1, Apo-E, IGF-1, Profilin1, and Col1a1) represent critical biological markers in pulmonary artery disease caused by CMS.

CONCLUSIONS

Irbesartan significantly improved pulmonary artery damage in a rat model of CMS possibly by impacting on the cholesterol metabolism pathway and by reducing damage to vascular endothelial cells. Irbesartan also inhibited the expression levels of IGF-1, Profilin1 and Col1a1 to relieve pulmonary artery pressure and improve lung function by inhibiting vascular remodeling. Several proteins were identified as potential biomarkers of CMS, including Apo-A1, Apo-C1, Apo-E, IGF-1, Profilin1, and Col1a1.

Enhancing waste activated sludge dewaterability by reducing interaction energy of sludge flocs

How to efficiently improve waste activated sludge (WAS) dewaterability is a common challenge in WAS treatment and management throughout world. The interaction energy of sludge flocs is of great importance for sludge dewaterability. In this study, the relationship among the repulsive force of sludge flocs, hydrophilic/hydrophobic characteristics of sludge flocs, and sludge dewaterability have been quantitatively and qualitatively investigated based on extended Derjaguin-Landau-Verwey-Overbeek theory for the first time. The energy barrier of sludge flocs has good correlations with sludge dewaterability (p < 0.05). Trivalent cations (Al³⁺ and Fe³⁺) and Fenton's reagent reduced the interfacial free energy (ΔG) from 9.4 mJ/m² of raw sludge to -34.2 (Al³⁺), -60.5 (Fe³⁺), and -63.2 (Fenton) mJ/m², respectively, indicating that the hydrophilic surfaces of the sludge flocs converted to hydrophobic (△G < 0), and decreasing Lewis acid-base interaction energy (W_AB) of sludge flocs. In addition, most of the trivalent cations (Al³⁺ and Fe³⁺) were attached to sludge flocs, leading to neutralize negative charges and mitigate electrostatic interaction energy (W_R) of sludge flocs. The reduction of W_AB and W_R eliminated energy barrier of sludge flocs and repulsive force between sludge flocs. In comparison, monovalent (Na⁺ and K⁺) and bivalent (Ca²⁺ and Mn²⁺) cations cannot completely change the hydrophilic surface characteristic and negative charge of sludge flocs. The existed energy barrier prevented sludge flocs to agglomerate with each other, thus resulting in a worse dewaterability. This study illustrated that reducing interaction energy of sludge flocs played a critical role to improve sludge dewaterability.

Tween 20 regulate the function and structure of transmembrane proteins of Bacillus cereus: Promoting transmembrane transport of fluoranthene

Polycyclic aromatic hydrocarbons (PAHs) are degraded by the highly efficient degrading bacterium Bacillus cereus. Transmembrane transport is highly important in PAH degradation by bacteria. Surfactants are the key substances that promote PAH adsorption, uptake and transmembrane transport by Bacillus cereus. In this study, the isobaric tags for relative and absolute quantitation (iTRAQ) approach was used for high-throughput screening of key functional proteins during transmembrane fluoranthene transport by Bacillus cereus treated with Tween 20. In addition, SWISS-MODEL was used to simulate the tertiary structures of key transmembrane proteins and analyze how Tween 20 promotes transmembrane transport. Transmembrane fluoranthene transport into Bacillus cereus requires transmembrane proteins and energy. Tween 20 was observed to improve bacterial motility and transmembrane protein expression. The interior of representative transmembrane proteins is mostly composed of hydrophobic β-sheets while amphipathic α-helices are primarily distributed at their periphery. The primary reason for this configuration may be α-helices promote the aggregation of surfactants and the phospholipid bilayer and the β-sheets promote surfactant insertion into the phospholipid bilayer to enhance PAH transport into Bacillus cereus. Investigating the effect of Tween 20 on Bacillus cereus transmembrane proteins during transmembrane fluoranthene transport is important for understanding the mechanism of PAH degradation by microorganisms.

Mechanism insights into polyhydroxyalkanoate-regulated denitrification from the perspective of pericytoplasmic nitrate reductase expression

For enhanced biological nutrient removal (BNR) process, the polyhydroxyalkanoate (PHA) can be used as an eco-friendly internal as well as external substrate for regulating the growth of heterotrophic denitrifiers and promoting the denitrification process for deep nitrogen removal from wastewater. However, the exact mechanisms by which PHA impacts bacterial metabolism and affects the electron transfer of denitrification remain unknown. In this study, the in-depth mechanism investigation for PHA-mediated denitrification based on the jointly applied transcriptomic, proteomic and Western Blotting techniques was performed on a model denitrifier, Pseudomonas stutzeri. Results showed that PHA dramatically fostered the growth of Pseudomonas stutzeri, resulting in improved nitrate removal efficiency from 32.8% to 45.8%. Comparison of protein expression profiles indicated that PHA promoted the expression of enzyme NapB and NapA by approximately 10.34 and 20.01 times, respectively, which were both in charge of reduction from nitrate to nitrite. Based on transcriptional sequencing and Tandem Mass Tags, the correlation results also showed that differential proteins and genes with the same expression trend were positively correlated (R² = 0.427, p-value<0.033). Western Blotting approach was further developed to confirm the up-regulated expression of target protein with the higher proportion of PHA in carbon source of the medium, which proved the reliability of proteomics results. All the findings presented here are believed to deepen the understanding of microbial mechanism about PHA-enhanced denitrification from the novel perspective of associated electron-transfer enzymatic proteins.

Changes in the characteristics of dissolved organic matter during sludge treatment: A critical review

Dissolved organic matter (DOM) of sludge is a heterogeneous mixture of high to low molecular weight organic substances which is including proteinaceous compounds, carbohydrates, humic substances, lipids, lignins, organic acids, organic micropollutants and other biological derived substances generated during wastewater treatment. This paper reviews definition, composition, quantification, and transformation of DOM during different sludge treatments, and the complex interplay of DOM with microbial communities. In anaerobic digestion, anaerobic digestion-refractory organic matter, particularly compounds showing polycyclic steroid-like, alkane and aromatic structures can be generated after pretreatment. During dewatering, the DOM fraction of low molecular weight proteins (< 20,000 Dalton) is the key parameter deteriorating sludge dewaterability. During composting, decomposition and polymerization of DOM occur, followed by the formation of humic substances. During landfill treatment, the composition of DOM, particularly humic substances, are related with leachate quality. Finally, suggestions are proposed for a better understanding of the transformation and degradation of DOM during sludge treatment. Future work in sludge studies needs the establishment and implementation of definitions for sample handling and the standardization of DOM methods for analysis, including sample preparation and fractionation, and data integration. A more detailed knowledge of DOM in sludge facilitates the operation and optimization of sludge treatment technologies.

Persulfate oxidation for alternative sludge treatment and nutrient recovery: An assessment of technical and economic feasibility

The introduce of tighter waste disposal regulations and increasing resource scarcity make the re-utilization of waste activated sludge a hot and crucial research topic. Compared with traditional sludge disposal technologies (e.g. landfill and incineration), advanced oxidation processes have been proven to be an environmentally friendly method for sludge stabilization and disintegration. However, the effectiveness of persulfate oxidation for sludge degradation, and the re-utilization of its embedded nutrients have been rarely reported. Therefore, this work is to investigate the technical and economic feasibility of using persulfate oxidation and struvite precipitation for sludge degradation and nutrient recovery. The results show that with the assistance of ultraviolet radiation, released phosphate and ammonia nitrogen from sludge could reach 233.4 and 265.6 mg/L. Besides, 92.8% phosphate and 32.6% ammonia-nitrogen could be recovered by struvite precipitation at a pH of 9.5, with an Mg: P molar ratio of 1.1:1. The economic analysis shows that the operational cost of the proposed process was 25% higher than traditional sludge disposal (267.5 $/ton), but its capital investment is much lower. Investigations on chemical dosage minimization, energy reclamation and process optimization are suggested to reduce the process's operating cost in the future.

Antibiotic resistance genes, bacterial communities, and functions in constructed wetland-microbial fuel cells: Responses to the co-stresses of antibiotics and zinc

The effects of the continuous accumulation of Zinc (Zn) on the fate of antibiotic resistance genes (ARGs) in constructed wetland-microbial fuel cells (CW-MFCs) remain unclear. In this study, the impacts of Zn addition and a circuit mode on antibiotic removal, occurrence of ARGs, the bacterial community, and bacterial functions were investigated in three groups of CW-MFCs. The results showed that continuous Zn exposure enriched the target ARGs during the initial stage, while excessive Zn accumulation decreased antibiotic removal and the abundance of ARGs. A principal component analysis demonstrated that ARGs and the bacterial community distribution characteristics were significantly impacted by the mass accumulation of antibiotics and Zn, as well as the circuit mode. A redundancy analysis, partial least squares path modeling, and Procrustes analysis revealed that the accumulation of antibiotics and Zn, the composition of the bacterial community, the circuit mode, and the abundance of intI associated with horizontal gene transfer jointly contributed to the distributions of ARGs in the electrodes and effluent. Moreover, continuous exposure to Zn decreased the bacterial diversity and changed the composition and function of the bacterial community predicted using PICRUSt tool. The co-occurrence of ARGs, their potential hosts and bacterial functions were further revealed using a network analysis. A variation partition analysis also showed that the accumulation of target pollutants and the circuit mode had a significant impact on the bacterial community composition and functions. Therefore, the interaction among ARGs, the bacterial community, bacterial functions, and pollutant accumulations in the CW-MFC was complex. This study provides useful implications for the application of CW-MFCs for the treatment of wastewater contaminated with antibiotics and heavy metals.

Critical review on dewatering of sewage sludge: Influential mechanism, conditioning technologies and implications to sludge re-utilizations

Sewage sludge (mainly composed of excessive bio-sludge) is an inevitable by-product of biological wastewater treatment process and contains various toxic substances, such as pathogens, heavy metals, and organic contaminants. The production of sewage sludge may cause serious pollution risks without appropriate disposals. As the essential step of sludge treatment, dewatering plays significant roles in minimizing the sludge volume, facilitating the transportation, increasing the calorific value and even reducing the leachate production in landfill sites. This paper presents a comprehensive review on the issues related to dewatering of sewage sludge. Section 1 starts with the environmental implications of sludge dewatering. Section 2 deals with the concepts and challenges about differentiation of bound water fractions, and also reviews the recent progress of in-situ visualization of water occurrence states in bio-flocs. Section 3 discusses about how various physiochemical properties influence the sludge dewaterability, and the insufficiency in in-situ micro-characterization of sludge constituents is pointed out. Section 4 reviews the existing conditioning technologies for sludge dewaterability improvement, and the advantages/disadvantages of each technology in terms of applicable occasions, material consumption, energy consumption and environmental impacts are evaluated. The last section (section 5) specifically analyzes the feasibility of integrating sludge dewatering and re-utilization, and raises attention to the potential environmental risks of dewatering conditioning. Based on the above discussion, we propose that a unified theory for sludge dewaterability improvement remains to be established. Especially, how the molecular structures of sludge compositions affect the solid-water interface behavior requires to be deepened, which will further unravel the mechanism behind strong water-holding capacities of bio-flocs. Additionally, we believe that the key challenges for sludge dewatering is how to select the appropriate conditioning technique according to the physiochemical properties of target sludge. The reliable indicators for real-time control of conditioning operations are still deficient, e.g., dynamic dosage control of conditioning chemicals. Accordingly, the potential environmental risks of excessive conditioning chemicals should be taken into more consideration.

New insights into filamentous sludge bulking: The potential role of extracellular polymeric substances in sludge bulking in the activated sludge process

The control of filamentous sludge bulking has been regarded as an important issue in the activated sludge process due to there is still a lack of understanding of the bulking mechanisms. In this study, changes in the extracellular polymeric substances (EPS) and metabolic profile of bulking sludge based on the proteomics level was investigated to reveal the potential role of EPS in deteriorating sludge floc stability and structure during filamentous bulking. The results showed that the EPS content gradually decreased from 210.23 mg/g volatile suspended solids (VSS) to 131.34 mg/g VSS during sludge bulking. The protein (PN) content of the EPS significantly decreased from 173.33 mg/g VSS to 95.42 mg/g VSS during sludge bulking. However, a gradual increase in polysaccharides (PS) was observed. Bacterial aggregation was hindered by the changes in the EPS and its components. The excessive proliferation of filamentous bacteria had a significant effect on the molecular functions of the extracellular PN and metabolic pathways of the EPS. The proteins associated with the hydrophobic amino acid synthesis decreased, whereas the proteins associated with the hydrophilic amino acid synthesis increased during sludge bulking. Electric repulsion was the key factor affecting the aggregation and flocculation ability of the bacteria during sludge bulking. The changes in the EPS and its components induced by the excessive proliferation of filamentous bacteria resulted in a loose floc structure and poor settling performance during sludge bulking. These findings provide new insights into sludge bulking during the activated sludge process.

New insights into the effect of sludge proteins on the hydrophilic/hydrophobic properties that improve sludge dewaterability during anaerobic digestion

Extracellular polymer proteins have been reported to play an important role in enhancing sludge dewaterability during anaerobic digestion in our previous study. However, how the proteins in sludge determine sludge dewaterability remains to be determined. In this work, proteins from digested sludge were identified using label free proteomics analysis, and its hydrophilicity/hydrophobicity properties and functional groups were analysed. We determined that the microbial community variation between the three stages during the anaerobic digestion process was responsible for enhancing sludge dewaterability; The transformation from hydrophilicity to hydrophobicity of digested sludge surface is the result of functional groups distribution variation which caused by the proteins and microbial communities. This study provides a new insight into the development of anaerobic digestion based on sludge dewaterability.

Evolution and resistance of a microbial community exposed to Pb(II) wastewater

This study investigated the treatment performance of activated sludge on Pb(II)-containing wastewater, including contaminant removal efficiency, extracellular polymeric substances, pbrT gene content and the microbial community. The average removal efficiencies of ammonia nitrogen, chemical oxygen demand, total phosphorus, total nitrogen and Pb(II) were 40% ± 4%, 91% ± 3%, 95% ± 3%, 51% ± 5% and 92% ± 9% during the stable operation stage, respectively. Moreover, the extracellular polymeric substance -protein contents increased significantly from day 0 to day 60 (p < 0.05). The most abundant fluorescent component in extracellular polymeric substances was a humic acid-like substance, and its fluorescence intensity increased significantly from day 0 to day 60 (p < 0.05). Adsorption of negatively charged organic functional groups in extracellular polymeric substances was identified as a major component of the removal of Pb(II). Most of the denitrifying bacteria associated with nitrogen removal showed an increasing trend during the acclimation stage, which may have resulted in high total nitrogen removal efficiency. In addition, pbrT uptake protein was found to be responsible for the uptake of Pb(II) into cells. The abundance of the pbrT gene showed a downward trend (p < 0.05) after adding Pb(II), probably because expression of the pbrT gene was inhibited under Pb(II) stress. Sphingopyxis containing the pbrT gene was the dominant resistance genus, and its relative abundance increased significantly (p < 0.05) from day 0 to day 60. This study provided a theoretical basis for the treatment of Pb(II)-containing wastewater.

Dewatering of sewage sludge via thermal hydrolysis with ammonia-treated Fenton iron sludge as skeleton material

In this study, the alkaline hydrothermal ferric carbon (AHFC), which was prepared by hydrothermal liquefaction method using Fenton iron sludge with NH₃·H₂O, was used as a skeleton materials for the dewatering of sewage sludge (SS) via thermal hydrolysis. NH₂ functional group presented in the AHFC and nano-sized γ-Fe₂O₃ was anchored on the surface of AHFC. The NH₂ functional group notably promoted thermal hydrolysis of SS from the increasing of TOC and TN value. γ-Fe₂O₃ showed adsorption effect to the water, resulting in decline of the dewatering rate of SS in present condition. When 100% of AHFC was added, dewatering rate of SS was decreased by 19.93% (at 160 °C), 4.50% (at 180 °C) and 8.34% (at 200 °C) respectively. 3D-EEM results showed that the degree of hydrolysis was deepened when AHFC was added for the intensity of soluble microbial products decline. AHFC promoted the decomposition of protein to form heterocycle compounds in the resulting cake according to in situ FTIR results. The nano γ-Fe₂O₃ catalysis to cake also can be observed for the activation energy was lower than blank in the range of 40˜60%. The study demonstrated concept and the effectiveness the reuse/recycle of the Fenton iron sludge for dewatering of SS.

Identification and function of extracellular protein in wastewater treatment using proteomic approaches: A minireview

Microbial extracellular proteins serve as important functions in wastewater treatment process. Analysis of their compositions and properties is crucial to probe their specific functions. However, conventional analytical techniques cannot obtain interest protein information from complex proteins. Recently, the extracellular proteomics method has been applied to resolve the composition of extracellular proteins. In order to better understand the roles of extracellular protein in wastewater treatment process, this review provides the information on the proteomics methods and their application in investigating extracellular proteins involved in microbial attachment/aggregation, biodegradation of pollutants, and response to environmental stresses. Future work needs to exploit the full capability of the proteome.

Linking Exoproteome Function and Structure to Anammox Biofilm Development

Extracellular proteins are of paramount importance in the cell-cell interactions of anammox biofilms. However, the inherent aggregation mechanisms of anammox have largely remained elusive. Herein, using a quartz sand extraction protocol and follow-up iTRAQ-based quantitative proteomics, we identified 367 extracellular proteins from initial colonizers, mature biofilm, and detached biofilm. The extracellular proteins were mainly membrane-associated. Most of the recovered proteins (226, 72.5%) originated from the phylum Planctomycetes. In summary, 215 and 190 of the 367 proteins recovered were up- and/or downregulated at least 1.2-fold during the biofilm formation and detachment periods, respectively. These differentially expressed proteins were dominantly involved in metal ion binding, which was regarded as strong evidence for their abilities to enhance ionic bridges in extracellular polymeric substances (EPS). Scanning electron microscopy-energy-dispersive X-ray spectroscopy (SEM-EDX) analysis of the biofilms further showed substantial levels of calcium and iron minerals. Critically, representative Sec-dependent secretory proteins affiliated with coccoid Planctomycetes, rod-shaped Proteobacteria, and filamentous Chloroflexi (11, 4, and 2 with differential expression, respectively) were found to have typical and abundant inner β-sheet structures, wherein hydrophobic moieties can promote anammox aggregation. Overall, these findings highlight links between differentially expressed protein functions and morphologic traits of anammox consortia during biofilm development.

Mechanism insights into bio-floc bound water transformation based on synchrotron X-ray computed microtomography and viscoelastic acoustic response analysis

This study visually tracked the micro-spatial water distribution in bio-flocs of waste activated sludge through in situ synchrotron X-ray computed microtomography. Primarily, the two fractions of bound water, the vicinal water adhering to the surface of organic compositions and the interstitial water mechanically trapped in the net-like structure of bio-flocs, were proposed based on the cross-section imaging results. Furthermore, the determinants on bound water occurrences were explored in terms of viscoelastic acoustic responses of extracellular polymeric substances (EPS). The joint roles of hydrophilic substance removal, EPS aggregation compaction and colloidal instability of sludge flocs in bound water reduction were confirmed by the strong correlations (Pearson correlation coefficient, R_p > 0.95, p-value<0.04) among protein levels of EPS, EPS viscosity and bound water contents. Accordingly, providing adhering sites for vicinal water and forming bio-flocs with high viscosity for trapping interstitial water were proposed to be the contributions of EPS on bound water occurrences.

Protein corona between nanoparticles and bacterial proteins in activated sludge: Characterization and effect on nanoparticle aggregation

In this work, the protein coronas of activated sludge proteins on TiO₂ nanoparticles (TNPs) and ZnO nanoparticles (ZNPs) were characterized. The proteins with high affinity to TNPs and ZNPs were identified by shotgun proteomics, and their effects of on the distributions of TNPs and ZNPs in activated sludge were concluded. In addition, the effects of protein coronas on the aggregations of TNPs and ZNPs were evaluated. Thirty and nine proteins with high affinities to TNPs and ZNPs were identified, respectively. The proteomics and adsorption isotherms demonstrated that activated sludge had a higher affinity to TNPs than to ZNPs. The aggregation percentages of ZNPs at 35, 53, and 106 mg/L of proteins were 13%, 14%, and 18%, respectively, whereas those of TNPs were 21%, 30%, 41%, respectively. The proteins contributed to ZNPs aggregation by dissolved Zn ion-bridging, whereas the increasing protein concentrations enhanced the TNPs aggregation through macromolecule bridging flocculation.

Metaproteomic analysis of the relationship between microbial community phylogeny, function and metabolic activity during biohydrogen-methane coproduction under short-term hydrothermal pretreatment from food waste

Short-term hydrothermal pretreatment (SHP) is an attractive method for food waste anaerobic digestion, which facilitates the solubilisation of recalcitrant particles. This study employed metaproteomic method to evaluate the relationships among microbial community phylogeny, function, and metabolic activity during two-stage anaerobic digestion under SHP (SHPT) from food waste. The presence of 651 bacterial proteins and 477 archaeal protein has been detected by liquid chromatography online linked to mass spectrometry, revealing a high metabolic heterogeneity during SHPT. The different stages of SHPT highlighted important roles for the bacterial proteins from Gammaproteobacteria, Bacilli, and Clostridia and the archaeal proteins from Methanosarcinales. The identified proteins related to biohydrogen production come from pyruvic acid decarboxylase and formic acid decomposition pathway in carbohydrate metabolism and methanogenesis from acetate, CO₂ and a methylotrophic pathway during energy metabolism. This could provide functional evidence of the metabolic activities and biogas production during SHPT.

Occurrence State and Molecular Structure Analysis of Extracellular Proteins with Implications on the Dewaterability of Waste-Activated Sludge

The occurrence state and molecular structure of extracellular proteins were analyzed to reveal the influencing factors on the water-holding capacities of protein-like substances in waste-activated sludge (WAS). The gelation process of extracellular proteins verified that advanced oxidation processes (AOPs) for WAS dewaterability improvement eliminated the water affinity of extracellular proteins and prevented these macromolecules from forming stable colloidal aggregates. Isobaric tags for relative and absolute quantitation proteomics identified that most of the extracellular proteins were originally derived from the intracellular part and the proteins originally located in the extracellular part were mainly membrane-associated. The main mechanism of extracellular protein transformation during AOPs could be represented by the damage of the membrane or related external encapsulating structure and the release of intracellular substances. For the selected representative extracellular proteins, the strong correlation (R² > 0.97, p < 0.03) between the surface hydrophilicity index and α-helix percentages in the secondary structure indicated that the water affinity relied more on the spatial distribution of hydrophilic functional groups rather than the content. Destructing the secondary structure represented by the α-helix and stretching the polypeptide aggregation in the water phase through disulfide bond removal might be the key to eliminating the inhibitory effects of extracellular proteins on the interstitial water removal from WAS.