Pasteurella haemolytica leukotoxin induced apoptosis of bovine lymphocytes involves DNA fragmentation

The fate of pharmaceuticals and personal care products (PPCPs) in sewer sediments:Adsorption triggering resistance gene proliferation

In recent years, large quantities of pharmaceuticals and personal care products (PPCPs) have been discharged into sewers, while the mechanisms of PPCPs enrichment in sewer sediments have rarely been revealed. In this study, three PPCPs (tetracycline, sulfamethoxazole, and triclocarban) were added consecutively over a 90-day experimental period to reveal the mechanisms of PPCPs enrichment and the transmission of resistance genes in sewer sediments. The results showed that tetracycline (TC) and triclocarban (TCC) have higher adsorption concentration in sediments compared to sulfamethoxazole (SMX). The absolute abundance of Tets and suls genes increased in sediments under PPCPs pressure. The increase in secretion of extracellular polymeric substances (EPS) and the loosening of the structure exposed a large number of hydrophobic functional groups, which promoted the adsorption of PPCPs. The absolute abundance of antibiotic resistance genes (ARGs), EPS and the content of PPCPs in sediments exhibited significant correlations. The enrichment of PPCPs in sediments was attributed to the accumulation of EPS, which led to the proliferation of ARGs. These findings contributed to further understanding of the fate of PPCPs in sewer sediments and opened a new perspective for consideration of controlling the proliferation of resistance genes.

The feasibility and applicability of sequential extraction of high value-added biogenic materials from sewage sludge

The sequential extraction routes of biogenic materials from sewage sludge (SS) were investigated. Physical methods (ultrasound, heating) and chemical methods (sodium hydroxide, sodium carbonate) were used to extract extracellular polymeric substances (EPS) and alginate-like extracellular polymers (ALEs) from SS. The residues after extraction were further subjected to physical methods (heating) and chemical methods (sulfuric acid, sodium hydroxide) for protein extraction. A comparison was made between sequential extraction routes and direct extraction of biomaterials from sludge in terms of extraction quantity, material properties, and applicability. The results showed that sequential extraction of biomaterials is feasible. The highest extraction quantities were obtained when using sodium carbonate for EPS and ALE extraction and sodium hydroxide for protein, reaching 449.80 mg/gVSS, 109.78 mg/gVSS, and 5447.08 mg/L, respectively. Sequential extraction procedures facilitate the extraction of biomaterials. Finally, suitable extraction methods for different application scenarios were analyzed.

Endogenous biopolymer hydrolysis for enhancing short-chain fatty acids recovery from excess sludge: Combination of lysozyme-catalyzing and cation exchange resin-mediated metal regulation

In decades, anaerobic fermentation with short-chain fatty acids (SCFAs) recovery from excess sludge have attained rising attention. However, rigid particulate organic matter (POMs) structure with slow hydrolysis limited anaerobic fermentation performance of excess sludge. Remarkable sludge hydrolysis performance was supposed to be achievable by the synchronous EPS repture and microbial cell lysis. This study clarified the improvement of overall anaerobic fermentation performance by combination treatment of lysozyme (Lyso) catalysis and metal regulation (MR). The Lyso + MR treatment triggered EPS rupture by protein structure deflocculation while catalyzing microbial cell lysis, which promoted massive extracellular and intracellular POMs hydrolysis. As a result, a significant amount of SCOD (5646.67 mg/L) was produced. Such endogenous organic matters hydrolysis led to considerable SCFAs accumulation (3651.14 mg COD/L) through 48-h anaerobic fermentation at 1.75 g/g SS cation-exchange resin and Lyso dosage of 10% (w/w), which was 5.945 times higher than that in the control. Additionally, it suggested that most of the recovered SCFAs remained in fermentative liquid after chemical conditioning and mechanical dewatering towards solid-liquid separation, which provided considerable economic benefit of 363.6-1059.1 CNY/ton SS.

Investigation of sludge disintegration using vortex cavitation circulating fluidised grinding technology

Waste-activated sludge (WAS) is regarded as a source of hazardous waste pollution from sewage treatment plants. To efficiently deal with WAS, vortex cavitation circulating fluidised grinding technology (VCCFGT) was proposed as a novel circulating fluidisation technology (CFT) to disintegrate WAS. To be specific, we investigated the effects of disintegration duration, pressure, and filling ratio of mill balls on sludge disintegration. The results of chemical and physical evaluation showed that the values of soluble chemical oxygen demand (SCOD), disintegration degree (DD_SCOD), DNA, protein, carbohydrate, and NH₄⁺-N increased with the increase in the filling ratio of the mill balls. Under a pressure and filling ratio of 0.30 MPa and 1.6%, respectively, the maximum effect was achieved after 60 min of treatment. Compared to those in the treatment without mill balls, the values of SCOD, DD_SCOD, DNA, protein, carbohydrate, and NH₄⁺-N in the treatment using mill balls increased by 218, 229, 230, 177, 371, and 190%, respectively. As a result of this technology, the temperature of the sludge dramatically increased, rising approximately 42.9 °C. Compared to that of the raw sludge, the sludge particle size after treatment was reduced by 83.25% at most, and the morphology of the sludge comprised smaller flocs. Compared to that of the ball-milling method, the mill balls filling ratio of VCCFGT reduced by 93.60-98.12%. Compared to that of sludge disintegration by the vortex cavitation method, VCCFGT indicating good disintegration degree (increased by 229%) and economic feasibility. VCCFGT has good application prospects for sludge disintegration. The main mechanisms of sludge disintegration and organic release include centrifugal force, grinding, shear force, cavitation, and cyclic fatigue effects, among which grinding plays a leading role. This study concluded that CFT can effectively disintegrate sludge flocs and disrupt bacterial cell walls.

Enhanced acidogenic fermentation from Al-rich waste activated sludge by combining lysozyme and sodium citrate pretreatment: Perspectives of Al stabilization and enzyme activity

The accumulation of poly aluminum chloride (PAC) in dewatered waste activated sludge (WAS) can cause severe Al pollution and significantly reduce the production of volatile fatty acids (VFAs) from anaerobic fermentation. Herein, the combination of lysozyme and sodium citrate pretreatment was applied to stabilize the aluminum and enhance the VFAs production via anaerobic fermentation. The complexation and stabilization of aluminum by the citrate was efficient, which is conducive to relieving the inhibition of aluminum on lysozymes and other extracellular hydrolases. Compared with the control group, the lysozyme, protease and α-glucosidase activities were obtained at 1.86, 1.72, and 1.15 times, respectively, following the pretreatment. 129.71 mg/g volatile suspended solids (VSS) of soluble proteins and 26.3 mg/g VSS of polysaccharides were obtained within 4 h, together with the degradation of 124 % more proteins and 75 % more polysaccharides within three days. This provided a sufficient number of substrates for VFA production. 588.4 mg COD/g VSS of total VFAs were obtained after the six-day anaerobic fermentation from Al-rich WAS following the combination of lysozyme and sodium citrate pretreatment, which was 7.3 times higher than that of the control group. This study presents a novel approach for enhancing VFA production in anaerobic fermentation as well as reducing risk of Al hazards from Al-rich WAS.

Optimum relative frequency and fluctuating substrate selection in reinforcing anammox-mediated anabolic adaptation

Adaptation to substrate fluctuations is a life actuality of microbes in global municipal wastewater treatment plants (WWTPs). Yet there remains a lack of definite information on how influent changes with different alternation frequencies shape the stability of anammox consortia and the metabolic regulations they feedback. According to human rhythmic activity, day-fluctuant fed (every 6 h, alternating between 50 and 100 mg NH₄⁺-N/L) substantially diminished the robustness of nitrogen removal efficiency (NRE; 84.1 ± 7.0%, left-skewed distribution [R² = 0.87]) and shock-resistance ability (>30% effluent variability). Unexpectedly, the anammox ecosystem under week-fluctuant mode (every 6 d) displayed adapted growth (NRE 86.6 ± 3.1%, normal distribution [R² = 0.97]), higher extracellular polymeric substances (EPS) yields, and superior tolerance (juggling the shortest recovery time and highest NRE, tightest protein secondary structure facing long-term load shocks) than steady-state (75 mg NH₄⁺-N/L). 16S sequencing showed that the influent disturbance led to increased levels of bacterial diversity, however, a similar microbiota composition between week-fluctuant and steady systems was detected. Notably, K strategist Candidatus Kuenenia was more sensitive to substrate fluctuations, with the lower relative abundance at day-fluctuant (23.4 ± 5.1%) and week-fluctuant (39.5 ± 4.3%) than at steady-state community (47.5 ± 4.2%). Conversely, Candidatus Jettenia had higher relative abundance at day-fluctuant (i.e., 1.3 ± 0.1%) compared to that at week-fluctuant (0.2 ± 0.04%) and steady-state (0.05 ± 0.03%). Importantly, untargeted metabolomics revealed that week-fluctuant grown anammox microbiota increased protein synthesis and transporter expression while decreasing expression of catabolic pathways (citric acid cycle and bypass) as a strategy for efficient substrate uptake and utilization, which clearly different to day-fluctuant and steady-state survival ways. Overall, we predictively reported an "anabolic adaptation growth state" for the anammox consortia and put forward the associated reinforcement control strategy.

Mechanism of dielectric barrier plasma technology to improve the quantity and quality of short chain fatty acids in anaerobic fermentation of cyanobacteria

The recycling of high value carbon resources from cyanobacteria has become a research hotspot. This work investigated the possibility of dielectric barrier discharge (DBD) plasma pretreatment to improve the anaerobic fermentation performance of cyanobacteria. The maximum accumulations of short-chain fatty acids (SCFAs) and acetic acid in DBD group were 3.30 and 1.49 times of that in control group. The physical effects of DBD plasma and the oxidative stress response of cyanobacteria cells could improve the solubilization of cyanobacteria polymer. The destruction of humus by DBD plasma can reduce the negative impact of humus on the early stage of anaerobic fermentation, thus facilitating the rapid start of anaerobic fermentation. The contents of Bacteroidetes, Firmicutes and Chloroflexi in DBD group were higher than those in control group, while the content of Proteobacteria was on the contrary, which was conducive to the hydrolysis and acidification process. The decrease of Methanosaeta sp. and Methanosarcina sp. abundance in DBD group might be another reason for the increase of acetic acid ratio. Under the joint action of plasma chemical oxidation and microbial degradation, the degradation effect of microcystin-LR in the anaerobic fermentation supernatant of DBD group was better than that of the control group, which was conducive to the recycling of cyanobacteria anaerobic fermentation supernatant. Therefore, DBD pretreatment was conductive to recycling valuable carbon source from cyanobacteria and can be further developed as a potential new pretreatment technology.

Characteristics of EPS from Pseudomonas aeruginosa and Alcaligenes faecalis under Cd(II) stress: changes in chemical components and adsorption performance

EPS (extracellular polymeric substance) production is a self-protection mechanism by which microorganisms slow or eliminate adverse effects in unfavorable environments. In this study, Pseudomonas aeruginosa and Alcaligenes faecalis were selected to explore changes in EPS components, especially protein components, under stress caused by different concentrations of Cd(II). The results showed that the protein content in EPS was the highest. The two strains achieved maximum EPS production levels of 109.17 and 214.96 mg/g VSS at Cd(II) stress concentrations of 20 and 50 mg/L, which were increased by 52.07% and 409.69% compared with the levels exhibited before stress, respectively. The protein content correlated very well with data from adsorption experiments. Furthermore, FTIR, 3D-EEM, and XPS results illustrated that after Cd(II) stress, C-N, C=O/-COOH, and R-NO₂^- moieties were formed in substantial quantities, and the stress effects of Pseudomonas aeruginosa were significantly higher than those of Alcaligenes faecalis. The results of this study showed that addition of Cd(NO₃)₂ effectively regulated the components of EPS, especially the protein content, and improved the adsorption capacity, which has application prospects for prevention and control of heavy metals.

Sludge reduction and microbial community evolution of activated sludge induced by metabolic uncoupler o-chlorophenol in long-term anaerobic-oxic process

Excess sludge management is a restrictive factor for the development of municipal wastewater treatment plants. The addition of metabolic uncouplers has been proven to be effective in sludge reduction. However, the long-term effect of metabolic uncoupler o-chlorophenol (oCP) on the biological wastewater treatment system operated in anaerobic-oxic mode is still unclear. To this end, two parallel reactors operated in anaerobic-oxic mode with and without 10 mg/L of oCP addition were investigated for 91 days. The results showed that 56.1 ± 2.3% of sludge reduction was achieved in the oCP-added system, and the nitrogen and phosphorus removal ability were negatively affected. Dosing oCP stimulated the formation of microbial products and increased the DNA concentration, but resulted in a decrease in the electronic transport activity of activated sludge. Microbial community analysis further demonstrated that a significant reduction of bacterial richness and diversity occurred after oCP dosing. However, after stopping oCP addition, the pollutant removal ability of activated sludge was gradually increased, but the sludge yield, as well as species richness and diversity, did not recover to the previous level. This study will provide insightful guidance on the long-term application of metabolic uncouplers in the activated sludge system.

Impact of magnesium ions on lysozyme-triggered disintegration and solubilization of waste activated sludge

Lysozyme can efficiently accelerate solubilization and hydrolysis of waste activated sludge (WAS) for anerobic digestion. However, the effect of lysozyme was easily to be inhibited by metal ions in WAS. The impact of magnesium ions (Mg²⁺) on lysozyme catalyze WAS disintegration was investigated in this study. The effect of lysozyme on WAS hydrolysis could be hindered by Mg²⁺. Relatively high concentrations (>50 mg/L) of Mg²⁺ in sludge significantly reduced the release of soluble polysaccharides and proteins from WAS, while sulfate ions or chloride ions caused no such effect. Proteins were difficult to be extracted from extracellular polymeric substances (EPS) of WAS in the presence of Mg²⁺ (>10 mg/L) due to the divalent cation bridging (DCB) behavior, while the extraction of polysaccharides was not significantly affected. The polysaccharides and proteins in the inner EPS layer were transferred to the outer layer during the lysozyme treatment, and total quantities of both components maintained constantly. At least 23.1% lysozymes were trapped in the liquid phase of 100 mg Mg²⁺/L in the first hour. Mg²⁺ could significantly affect the transfer of lysozyme from liquid phase to the inner layer of sludge. Mg²⁺ neutralized the negative surface charge of the sludge particles, which hindered the absorption of positively charged lysozyme molecules by sludge flocs from the liquid phase. The proteins of TB-EPS had higher ratios of α-helixes and tighter structures than those in LB-EPS, which could impede the lysozyme transfer to the cell wall.

A novel partial denitrification, anammox-biological phosphorus removal, fermentation and partial nitrification (PDA-PFPN) process for real domestic wastewater and waste activated sludge treatment

A novel process was developed for real domestic wastewater and waste activated sludge (WAS) treatment based on partial denitrification, anammox-biological phosphorus removal, fermentation and partial nitrification (PDA-PFPN). After 246 days of operation, the effluent concentrations of NH₄⁺-N, NO₂^--N and NO₃^--N were below detection limits (0.1 mg/L), and the effluent concentration of PO₄^3--P was 0.1 mg/L without the addition of external carbon source in PDA-PFPN system. Moreover, the sludge reduction efficiency reached 48.1% due to fermentation. The nitrite accumulation ratios by ammonia oxidation and nitrate reduction pathway were 60.6% and 87%, respectively. Intracellular metabolites measured by liquid chromatography mass spectrometer (LC-MS/MS) suggested that different intracellular amino acids were stored and consumed at different duration, and intracellular Valine, Glycine and Lysine were not utilized in oxic stage. Results of flow cytometry showed that the proportion of intact cells decreased from 94.7% to 82.9%, and necrotic cells increased from 5.3% to 17.1% with the increase of DNA content in sludge supernatant and cell decay rate, indicating the occurrence of cell death and lysis and leading to WAS reduction. Analysis of transcriptional community composition revealed that partial denitrification bacteria (Thauera), anammox bacteria (Candidatus Brocadia and Candidatus Kuenenia), simultaneous phosphorus removal and fermentation bacteria (Tetrasphaera) and partial nitrification bacteria (Nitrosomonas) coexisted and actually worked in PDA-PFPN system. The novel PDA-PFPN process simultaneously achieved highly efficient nitrogen and phosphorus removal and WAS reduction without the addition of external carbon source, which greatly reduced the operation cost of carbon source dosing and WAS treatment in wastewater treatment.

Effects of different exogenous cadmium compounds on the chemical composition and adsorption properties of two gram-negative bacterial EPS

Three different Cd(II) compounds were used to regulate Pseudomonas aeruginosa and Alcaligenes faecalis EPS (extracellular polymeric substances). The purpose of this study was to improve the content of EPS protein and the adsorption capacity of Cd(II) by different Cd(II) compounds. The results showed that Cd(NO₃)₂ had the best stress/induction effect on the two strains. Under the best stress/induction, the protein in EPS of the two strains increased most obviously, and the adsorption capacity of Cd(II) was increased by more than 40%. Under these conditions, the kinetics of the adsorption process of Cd(II) by Cd(NO₃)₂-EPS_{A. F} (EPS produced by Alcaligenes faecalis under Cd(NO₃)₂ stress) could be well fitted by the Langmuir isotherm model, and the theoretical maximum adsorption amount of 1111.11 mg/g EPS could be obtained. The results of 3D-EEM, FTIR and XPS indicated that proteins, especially CO, CN and NH in proteins, played a major role in the removal of Cd(II) by Cd(NO₃)₂-EPS_{A. F}. The results of this study show that the addition of Cd(NO₃)₂ can effectively regulate the content of chemical components, especially the content of protein, and thus greatly improve the removal efficiency of heavy metals, which shows great application prospects in the prevention and control of heavy metal pollution.

Achieving enhanced biological phosphorus removal utilizing waste activated sludge as sole carbon source and simultaneous sludge reduction in sequencing batch reactor

Achieving enhanced biological phosphorus removal dominated by Tetrasphaera utilizing waste activated sludge (WAS) as carbon source could solve the problems of insufficient carbon source and excessive discharge of WAS in biological phosphorus removal. Up to now, the sludge reduction ability of Tetrasphaera remained largely unknown. Furthermore, the difference between traditional sludge fermentation and sludge fermentation dominated by Tetrasphaera was still unclear. In this study, two different sequencing batch reactors (SBRs) were operated. WAS from SBR-parent was utilized as sole carbon source to enrich Tetrasphaera with the relative abundance of 91.9% in SBR-Tetrasphaera. PO₄^3--P removal and sludge reduction could simultaneously be achieved. The effluent concentration of PO₄^3--P was 0, and the sludge reduction efficiency reached about 44.14% without pretreatment of sludge. Cell integrity detected by flow cytometry, the increase of DNA concentration in the sludge supernatant and decrease of particle size of activated sludge indicated that cell death and lysis occurred in sludge reduction dominated by Tetrasphaera. Stable structure of activated sludge was also damaged in this process, which led to the sludge reduction. By analyzing the excitation-emission matrix spectra of extracellular polymeric substances and the changes of carbohydrate and protein concentration, this study proved that slowly biodegradable organics (e.g., soluble microbial byproduct, tyrosine and tryptophan aromatic protein) could be better hydrolyzed and acidized to volatile fatty acids (VFAs) in sludge fermentation dominated by Tetrasphaera than traditional sludge fermentation, which provided carbon source for biological nutrients removal and saved operation cost in wastewater treatment.

Perfluorooctane sulfonate decreases the performance of a sequencing batch reactor system and changes the sludge microbial community

The existence of perfluorooctane sulfonate (PFOS) in large quantities threatens environment biosafety. However, the fate of PFOS in a sequencing batch reactor (SBR) system and its influence in system has not yet been revealed. In this study, the fate and behavior of PFOS in an SBR processing system were investigated. Mass balance analyses revealed that PFOS removal was mainly through adsorption. After the reactors were run for 20 days, the PFOS (100 mg/L) removal rate was only 28%. Under the influence of PFOS, the removal rates of chemical oxygen demand (COD) and ammonia nitrogen dropped rapidly from 92, 98% to 23, 35% in the 20th day of system operation, respectively, while, accumulation of nitrite and nitrate was reduced. Compared with the control group, PFOS stimulates microorganisms to secrete more soluble microbial products (SMP) and extracellular polymeric substances (EPS). The adsorption of PFOS and EPS causes sludge bulking and decreases settling. The richness and diversity of microorganisms decreased significantly, affecting the system's removal of COD and ammonia nitrogen. Therefore, the SBR system is not suitable for treating wastewater containing PFOS. It is necessary to remove PFOS through pretreatment to reduce its impact on the SBR system.

Insight the roles of loosely-bound and tightly-bound extracellular polymeric substances on Cu2+, Zn2+ and Pb2+ biosorption process with Desulfovibrio vulgaris

The aim of this study is to explore the fate and mechanism of metal cations of biosorption in the Desulfovibrio vulgaris system (including bacterial cells and secreted loosely-bound extracellular polymeric substances (LB-EPS) and tightly-bound extracellular polymeric substances (TB-EPS)). The relative contribution of EPS (TB-EPS and LB-EPS) to the adsorption of three metal cations is much greater than that of bacterial cells, and the adsorption capacity of Pb²⁺ on EPS (TB-EPS and LB-EPS) is much greater than that of Cu²⁺ and Zn²⁺ (Pb²⁺ > Cu²⁺ > Zn²⁺). The order of absorption capacity was as follows: LB-EPS > TB-EPS > bacterial cells, the adsorption contribution of EPS (including TB-EPS and LB-EPS) to Cu²⁺, Zn²⁺ and Pb²⁺ accounted for total adsorption capacity was 82%, 83% and 86%, respectively. It was suggested that LB-EPS was the first reaction barrier of immobilization metal cations before metal cations was able to pass through EPS and react with cells. The adsorption process was dominated by complexation and electrostatic interaction. The three-dimensional excitation-emission matrix (3D-EEM) identified two main fluorescence peaks of the aromatic and tryptophan protein-like substances in EPS. According to the synchronous fluorescence spectra, the tryptophan protein-like substances were gradually quenched with increased metal cations concentrations, which the quencher mechanism is dynamic quenching. The findings of this work are significant to reveal the fate of Cu²⁺, Zn²⁺ and Pb²⁺ during its sorption process onto Desulfovibrio vulgaris, and provide useful information of the interaction between Desulfovibrio vulgaris and its secreted EPS with metal cations.

Effects of bacterial community composition and structure in drinking water distribution systems on biofilm formation and chlorine resistance

Community-intrinsic properties affect the composition and function of a microbial community. Understanding the microbial community-intrinsic properties in drinking water distribution systems (DWDS) could help to select disinfection strategies and aid in the prevention of waterborne infectious diseases. In this study, we investigated the formation of multi-species biofilms in six groups, each consisting of four or five mixed bacterial strains isolated from a simulated DWDS, at different incubation times (24, 48, and 72 h). We then evaluated the chlorine resistance of the 72-h multi-species biofilms in the presence of 0.3, 0.6, 1, 2, 4, and 10 mg/L residual chlorine. Microbacterium laevaniformans inhibited the formation of multi-species biofilms, Sphingomonas sp., Acinetobacter sp. and A. deluvii had the effect of promoting their growth, and B. cereus has little effect on the growth of multi-species biofilms. However, these inhibition and promotion effects were weak and inadequate to completely control the growth of multi-species biofilms. All multi-species produced strong biofilms after 72 h incubation, which could be due to microbial community-intrinsic properties. Community-intrinsic properties could maintain high EPS production and cell-to-cell connections in multi-species biofilms, and could affect the formation of multi-species biofilms. The chlorine resistance of multi-species biofilms was significantly improved by B. cereus, but significantly reduced by M. laevaniformans. These results indicated that the microbial community-intrinsic properties were influenced by the environment. At a relatively low disinfectant concentration (<2 mg/L residual chlorine), the community-intrinsic properties were maintained; however, when the disinfectant concentration was increased to 2-4 mg/L residual chlorine, the community-intrinsic properties weakened, and significantly affected the resistance of the microbial communities to the disinfectant. With further increases in concentration, to >4 mg/L residual chlorine, no significant difference was observed in the disinfectant resistance of the microbial community.

Genome-Centric Metagenomic Insights into the Impact of Alkaline/Acid and Thermal Sludge Pretreatment on the Microbiome in Digestion Sludge

Pretreatment of waste-activated sludge (WAS) is an effective way to destabilize sludge floc structure and release organic matter for improving sludge digestion efficiency. Nonetheless, information on the impact of WAS pretreatment on digestion sludge microbiomes, as well as mechanistic insights into how sludge pretreatment improves digestion performance, remains elusive. In this study, a genome-centric metagenomic approach was employed to investigate the digestion sludge microbiome in four sludge digesters with different types of feeding sludge: WAS pretreated with 0.25 mol/liter alkaline/acid (APAD), WAS pretreated with 0.8 mol/liter alkaline/acid (HS-APAD), thermally pretreated WAS (thermal-AD), and fresh WAS (control-AD). We retrieved 254 metagenome-assembled genomes (MAGs) to identify the key functional populations involved in the methanogenic digestion process. These MAGs span 28 phyla, including 69 yet-to-be-cultivated lineages, and 30 novel lineages were characterized with metabolic potential associated with hydrolysis and fermentation. Interestingly, functional populations involving carbohydrate digestion were enriched in APAD and HS-APAD, while lineages related to protein and lipid fermentation were enriched in thermal-AD, corroborating the idea that different substrates are released from alkaline/acid and thermal pretreatments. Among the major functional populations (i.e., fermenters, syntrophic acetogens, and methanogens), significant correlations between genome sizes and abundance of the fermenters were observed, particularly in APAD and HS-APAD, which had improved digestion performance.IMPORTANCE Wastewater treatment generates large amounts of waste-activated sludge (WAS), which consists mainly of recalcitrant microbial cells and particulate organic matter. Though WAS pretreatment is an effective way to release sludge organic matter for subsequent digestion, detailed information on the impact of the sludge pretreatment on the digestion sludge microbiome remains scarce. Our study provides unprecedented genome-centric metagenomic insights into how WAS pretreatments change the digestion sludge microbiomes, as well as their metabolic networks. Moreover, digestion sludge microbiomes could be a unique source for exploring microbial dark matter. These results may inform future optimization of methanogenic sludge digestion and resource recovery.

Sludge pre-treatments change performance and microbiome in methanogenic sludge digesters by releasing different sludge organic matter

In this study, temporal impacts of thermal, alkaline/acid and thermal-alkaline sludge pre-treatments on digestion performance and microbiome were investigated and compared in methanogenic sludge digesters. Results showed that thermal and alkaline/acid pre-treatments were efficient in releasing intracellular and EPS organic matter, respectively. The thermal-alkaline pre-treatment showed synergistic impacts of both thermal and alkaline/acid pre-treatments by releasing the major portion of sludge organic matter from solid- to liquid-phase, which result in 60-65% organic carbon removal in subsequent sludge digestion and further optimizing digestion temperature had negligible improvement. The 16S rRNA gene-based analyses suggested that organic matter released from sludge pre-treatments is a major deterministic parameter in shaping sludge microbiome. Pre-treatment specific lineages were identified in different sludge digesters, whereas several taxa were identified as common functionally active populations in sludge digestion. This study provided mechanistic insights into impacts of pre-treatments on digestion performance and microbiome in methanogenic sludge digesters.

Synergistic effect of biofilm growth and cadmium adsorption via compositional changes of extracellular matrix in montmorillonite system

The interaction of bacterial biofilm and clay minerals provides great potential for heavy metal remediation in contaminated soil, yet, little is known about how heavy metal, clay minerals and their combinations affect the bacterial biofilm performance and heavy metal adsorption. In this study, the response of biofilm development as well as Cd²⁺ adsorption in the presence of Cd²⁺ and montmorillonite has been deciphered. Low concentrations of Cd²⁺ and montmorillonite or their combinations enhanced biofilm formation by increasing polysaccharides proportion in the biofilm matrix, and the maximum adsorption capacity of Cd²⁺ by biofilm was increased by 1.5 times. Furthermore, the immobilization of Cd²⁺ by soil was significantly improved when S14-biofilm was introduced. Such results could gain deeper insight into bacterial survival tactics in the complex systems which makes major contribution to microbial remediation of heavy metal polluted environments.

Enhanced anaerobic fermentation of waste activated sludge by NaCl assistant hydrolysis strategy: Improved bio-production of short-chain fatty acids and feasibility of NaCl reuse

This study developed an economical approach for enhancing short-chain fatty acids (SCFAs) production from waste activated sludge (WAS) by NaCl assistant anaerobic fermentation. With NaCl addition at 20 g/L, sludge disintegration with extracellular polymeric substance (EPS) disruption and cell lysis were induced owing to the attack of osmotic pressure, which facilitated WAS solubilization with release of biodegradable organic matters. The SCOD sharply increased to 4092 mg/L (SCOD/TCOD = 23.9%) after 2-day hydrolysis, against 1462 mg/L in the control. After 4-day anaerobic fermentation, considerable SCFAs production of 288.2 mg COD/g VSS was achievable. More than 60% of the SCFAs was composed of acetic and propionic acids. The feasibility of bio-electrogenesis in microbial fuel cell (MFC) utilizing fermentative liquid was assessed. As such, the produced SCFAs could be consumed with energy recovery, thereby the used NaCl was reusable, which created environmental and economic benefits, e.g. reduced NaCl consumption and cost, negligible residual NaCl.

An innovative alkaline protease-based pretreatment approach for enhanced short-chain fatty acids production via a short-term anaerobic fermentation of waste activated sludge

This study reported a novel pretreatment approach with combination of alkaline protease (AP) and pH 10 for enhancing short-chain fatty acids (SCFAs) production from waste activated sludge (WAS). Through the AP-based pretreatment, WAS flocs were disintegrated with cell lysis, leading to release of biodegradable organic matters. At the external AP dosage of 5%, SCOD of 5363.7 mg/L (SCOD/TCOD = 32.5%) was achievable after 2-h pretreatment. More than 66% of SCOD was composed of proteins and carbohydrates. Considerable SCFAs of 607 mg COD/g VSS was produced over a short-term anaerobic fermentation of 3 days, which was 5.4 times higher than that in the control. Acetic and propionic acids accounted for 74.1% of the SCFAs. The AP-based approach increased endogenous protease and α-glucosidase activities, facilitating biodegradation of dissolved organic matters and SCFAs production. Such approach is promising for WAS disposal and carbon recovery, the produced SCFAs might supply 60% of carbon gap in wastewater.

Response of Bacillus vallismortis sp. EPS to exogenous sulfur stress/ induction and its adsorption performance on Cu(II)

The chemical composition of EPS (Extracellular Polymeric Substances) produced by Bacillus vallismortis sp. and its adsorption performance on typical heavy metal were studied under Na₂S stress/induction at different concentrations. Its structure was characterized by three-dimensional fluorescence spectrogram (3D-EEM), infrared spectrum (FTIR) and X-ray photoelectron spectroscopy (XPS). The results showed that, when the Na₂S stress/induction intensity was 20 mg/L, the protein concentration was nearly doubled compared with Control-EPS (EPS produced by Bacillus vallismortis sp. without exogenous sulfur stress); furthermore, the 3D-EEM results also demonstrated that there was an increase in the protein content, with the -SH content reaching 154.36 μmol/L, which was 48.2% higher than before stress (104.15 μmol/L). Under this condition, S-EPS (EPS produced by Bacillus vallismortis sp. stressed by exogenous sulfur) exhibited the best adsorption effect on Cu(II), with the theoretical maximum adsorption capacity reaching 1428.57 mg/g EPS. FTIR and XPS analyses revealed that the -SH, CO, N-H played a major role in the adsorption of Cu(II); among those, -SH played a key role. Moreover, the adsorption capacity of Cu(II) by S-EPS was correlated with the content of sulfhydryl protein; indeed, the exogenous sulfur stress/induction can effectively regulate the chemical composition of EPS and improve its adsorption performance, which can be crucial in the prevention and control of heavy metal pollution.

Biosorption Characteristics of Hg(II) from Aqueous Solution by the Biopolymer from Waste Activated Sludge

The divalent mercury ion (Hg(II)) is one of the most hazardous toxic heavy-metal ions, and an important industrial material as well. It is essential to remove and recover Hg(II) from wastewater before it is released into the environment. In this study, the biosorption characteristics of Hg(II) from aqueous solution by the biopolymer from waste activated sludge (WAS) are investigated. The major components of the biopolymer consisted of proteins, carbohydrates, and nucleic acids. The adsorption kinetics fit for the pseudo-second-order kinetic model, and the adsorption isotherms were well described by Langmuir equation. The adsorption capacity of the biopolymer increased along with rising temperature, and the maximal adsorption capacity was up to 477.0 mg Hg(II)/g biopolymer at 308 K. The infrared spectroscopy analyses showed that the complexation of Hg(II) by the biopolymer was achieved by the functional groups in the biopolymer, including hydroxyl (-OH), amino (-NH2), and carboxylic (-COOH). From the surface morphology, the special reticulate structure enabled the biopolymer to easily capture the metal ions. From the elemental components analyses, a part of Hg(II) ions was removed due to ion exchange with the Na+, K+, and Ca2+, in the biopolymer. Both complexation and ion exchange played key roles in the adsorption of Hg(II) by the biopolymer. These results are of major significance for removal and recovery of Hg(II) from wastewater.

Formation of microbial products by activated sludge in the presence of a metabolic uncoupler o-chlorophenol in long-term operated sequencing batch reactors

Metabolic uncouplers are widely used for reducing excess sludge in biological wastewater treatment systems. However, the formation of microbial products, such as extracellular polymeric substances, polyhydroxyalkanoate and soluble microbial products by activated sludge in the presence of metabolic uncouplers remains unrevealed. In this study, the impacts of a metabolic uncoupler o-chlorophenol (oCP) on the reduction of activated sludge yield and formation of microbial products in laboratory-scale sequencing batch reactors (SBRs) were evaluated for a long-term operation. The results show the average reduction of sludge yield in the four reactors was 17.40%, 25.80%, 33.02% and 39.50%, respectively, when dosing 5, 10, 15, and 20 mg/L oCP. The oCP addition slightly reduced the pollutant removal efficiency and decreased the formation of soluble microbial products in the SBRs, but stimulated the productions of extracellular polymeric substances and polyhydroxyalkanoate in activated sludge. Furthermore, the significant reduction of electronic transport system activity occurred after the oCP addition. Microbial community analysis of the activated sludge indicates dosing oCP resulted in a decrease of sludge richness and diversity in the SBRs. Hopefully, this study would provide useful information for reducing sludge yield in biological wastewater treatment systems and behaviors of activated sludge in the presence of uncouplers.

Performance and microbial community of the CANON process in a sequencing batch membrane bioreactor with elevated COD/N ratios

In this study, the effects of elevated chemical oxygen demand/nitrogen (COD/N) ratios on nitrogen removal, production and composition of the extracellular polymer substances (EPS) and microbial community of a completely autotrophic nitrogen removal via nitrite (CANON) process were studied in a sequencing batch membrane bioreactor (SBMBR). The whole experiment was divided into two stages: the CANON stage (without organic matter in influent) and the simultaneous partial nitrification, anaerobic ammonia oxidation and denitrification (SNAD) stage (with organic matter in influent). When the inflow ammonia nitrogen was 420 mg/L and the COD/N ratio was no higher than 0.8, the addition of COD was helpful to the CANON process; the total nitrogen removal efficiency (TNE) was improved from approximately 65% to more than 75%, and the nitrogen removal rate (NRR) was improved from approximately 0.255 kgN/(m³·d) to approximately 0.278 kgN/(m³•d), while the TNE decreased to 60%, and the NRR decreased to 0.236 kgN/(m³•d) when the COD/N ratio was elevated to 1.0. For the EPS, the amounts of soluble EPS (SEPS) and loosely bound EPS (LB-EPS) were both higher in the CANON stage than in the SNAD stage, while the amount of tightly bound EPS (TB-EPS) in the SNAD stage was significantly higher due to the proliferation of heterotrophic bacteria. The metagenome sequencing technique was used to analyse the microbial community in the SBMBR. The results showed that the addition of COD altered the structure of the bacterial community in the SBMBR. The amounts of Candidatus 'Anammoxoglobus' of anaerobic ammonia oxidation bacteria (AAOB) and Nitrosomonas of ammonia oxidizing bacteria (AOB) both decreased significantly, and Nitrospira of nitrite oxidizing bacteria (NOB) was always in the reactor, although the amount changed slightly. A proliferation of denitrifiers related to the genera of Thauera, Dokdonella and Azospira was found in the SBMBR.

Composition change and adsorption performance of EPS from Bacillus vallismortis sp. induced by Na2S

Sodium sulfide (Na₂S) was used as an inducer to regulate the components of Bacillus vallismortis sp. EPS (Extracellular Polymeric Substances). The main objective of this study was to improve the content of sulfhydryl protein and the adsorption property of EPS to Zn (Ⅱ) that as an typical heavy metal. The results showed that the maximum EPS production of 105.58 mg/g VSS coupling with doubled increase in protein in which the contant of -SH increased by 48.2% from 104.15 to 154.36 μmol/L were recorded in the presence of 20 mg/L Na₂S. Under this condition, the adsorption capacity of S-EPS (EPS with added exogenous Na₂S) for Zn (Ⅱ) was highest. The kinetics of the adsorption process of Zn (Ⅱ) by the S-EPS can be well fitted by the Langmuir isotherm model and the theoretical maximum adsorption amount of 979.09 mg/g EPS could be obtained. The results of 3D-EEM and FTIR analyses, illustrated that -SH, CO, and N-H/C-N played major roles in the removal of Zn (Ⅱ) by S-EPS. The results obtained in this study demonstrated that the addition of sulfur source could increase the content of sulfhydryl protein, and effectively regulate the content of chemical composition, expecially for the sulfhydryl of EPS, and thereby greatly improving the removal efficiency of heavy metals, which showed a great application prospect in the prevention and control of heavy metal pollution.

Response of microbes to biochar strengthen nitrogen removal in subsurface flow constructed wetlands: Microbial community structure and metabolite characteristics

Four subsurface flow constructed wetlands (SFCWs) were constructed on the basis of the volume ratio of biochar in common gravel (0%, 10%, 20%, and 30%) for the evaluation of microbe and metabolite characteristics response to biochar addition. The results showed that the biochar added SFCWs provided higher removal efficiencies for ammonium (49.69%-63.51%) and total nitrogen (81.83%-86.36%), compared with pure gravel packed SFCWs for ammonium (47.40%) and total nitrogen (80.75%), respectively. Illumina MiSeq sequencing results revealed that the dominant phyla were Proteobacteria, Bacteroidetes, and Firmicutes. Biochar addition can improve the removal of nitrogen by altering microbial community and increasing the relative abundance of Thauera, Candidatus Competibacter, Dechloromonas, Desulfobulbus, Chlorobium, and Thiobacillus. Protein and humic substances were the primary components of extracellular polymeric substance (EPS) in SFCWs. The amount of total EPS considerably decreased with biochar addition, which caused a shift in the EPS functional groups including carbonyl of protein, amide, and hydroxyl groups. Moreover, biochar could enhance the high molecular weight compounds metabolized into low molecular compounds. The results can provide new insights into the use of biochar in the enhancement of nitrogen removal by microbial community and metabolic product characteristics.

Channel Formation by LktA of Mannheimia (Pasteurella) haemolytica in Lipid Bilayer Membranes and Comparison of Channel Properties with Other RTX-Cytolysins

Cytolysin LktA is one of the major pathogenicity factors of Mannheimia haemolytica (formerly Pasteurella haemolytica) that is the cause of pasteurellosis, also known as shipping fever pneumonia, causing substantial loss of sheep and cattle during transport. LktA belongs to the family of RTX-toxins (Repeats in ToXins) that are produced as pathogenicity factors by a variety of Gram-negative bacteria. Sublytic concentrations of LktA cause inflammatory responses of ovine leukocytes. Higher concentrations result in formation of transmembrane channels in target cells that may cause cell lysis and apoptosis. In this study we investigated channel formation by LktA in artificial lipid bilayer membranes made of different lipids. LktA purified from culture supernatants by polyethylene glycol 4000 precipitation and lyophilization had to be activated to frequently form channels by solution in 6 M urea. The LktA channels had a single-channel conductance of about 60 pS in 0.1 M KCl, which is about one tenth of the conductance of most RTX-toxins with the exception of adenylate cyclase toxin of Bordetella pertussis. The LktA channels are highly cation-selective caused by negative net charges. The theoretical treatment of the conductance of LktA as a function of the bulk aqueous concentration allowed a rough estimate of the channel diameter, which is around 1.5 nm. The size of the LktA channel is discussed with respect to channels formed by other RTX-toxins. We present here the first investigation of LktA in a reconstituted system.

New method for algae comprehensive utilization: Algae-derived biochar enhances algae anaerobic fermentation for short-chain fatty acids production

Interest in the resource utilization of algae has gradually increased due to the frequent occurrence of harmful algal blooms. Here, biochar derived from algae was applied to algae anaerobic fermentation for short-chain fatty acids (SCFAs) production. In the presence of algae-derived biochar, the concentration of SCFAs within 4 d (4334 mg COD/L) was approximately doubled compared to the control (2016 mg COD/L), and the fermentation time for maximal SCFAs yield was shortened. Biochar improved the disruption of algae to release more intracellular macromolecular organics. Altering algae hydrolysis, the activity of hydrolase and the contents of functional gene were advantageous to SCFAs accumulation by providing more micromolecular organics in the presence of biochar. Additionally, the relative abundance and survival of acid-forming bacteria were enhanced significantly. Furthermore, biochar accelerated the electron transport and energy synthesis in the biological system, driving the biological reactions that allow microorganisms to function and life to flourish.

Characterization of the Fouling Layer on the Membrane Surface in a Membrane Bioreactor: Evolution of the Foulants' Composition and Aggregation Ability

In this study, the characteristics of membrane foulants were analyzed with regard to morphology, composition, and aggregation ability during the three stages of transmembrane pressure (TMP) development (fast-slow-fast rise in TMP) in a steady operational membrane bioreactor (MBR). The results obtained show that the fouling layer at the slow TMP-increase stage possessed a higher average roughness (71.27 nm) and increased fractal dimension (2.33), which resulted in a low membrane fouling rate (0.87 kPa/d). A higher extracellular DNA (eDNA) proportion (26.12%) in the extracellular polymeric substances (EPS) resulted in both higher zeta potential (-23.3 mV) and higher hydrophobicity (82.3%) for initial foulants, which induced and increased the protein proportion in the subsequent fouling layer (74.11%). Furthermore, the main composition of the EPS shifted from protein toward polysaccharide dominance in the final fouling layer. The aggregation test confirmed that eDNA was essential for foulant aggregation in the initial fouling layer, whereas ion interaction significantly affected foulant aggregation in the final fouling layer.

Potential metal-binding ability of proteins in the extracellular slime of Laccaria bicolor exposed to excessive Cu and Cd

Ectomycorrhizal fungi can enhance the tolerance of plants to heavy metal stress by reducing the accumulation of heavy metals in the aerial parts of the plants. Extracellular chelation is a major mechanism of heavy metal tolerance in ectomycorrhizal fungi in which extracellular slime plays a fundamental role. The objectives of this study were to investigate the potential metal-binding ability and the protein composition of extracellular slime. The extracellular slime of Laccaria bicolor (L. bicolor) cultivated under Cd²⁺ and Cu²⁺ stress was separated using various ultrasonic pre-treatments. The protein content, composition, and metal content of the extracellular slime were measured. The results showed that the protein content in the extracellular slime significantly increased under both Cd²⁺ and Cu²⁺ stress. The SDS-PAGE profile showed that Cd²⁺ and Cu²⁺ stress induced the expression of several new proteins. Heavy metal quantification revealed that the Cd content fixed in the extracellular slime accounted for 22-28% of the metal fixed by the fungal mycelia. Meanwhile, no Cu was detected in the fungal extracellular slime, implying that the extracellular slime may not be effective for the fixation of essential metallic elements such as Cu. Taken together, these results provided evidence that L. bicolor was able to ameliorate the intracellular Cd content by stimulating extracellular slime exudation and altering the composition of the proteins therein. Nevertheless, this blocking strategy may be effective only for the non-essential element Cd and was ineffective for the physiological element Cu.

Evaluation of the secondary structures of protein in the extracellular polymeric substances extracted from activated sludge by different methods

The changes of protein secondary structures in the extracellular polymeric substances (EPS) extracted from activated sludge by four different methods were studied by analyzing the amide I region (1700-1600 cm^-1) of the Fourier transform infrared spectra and model protein test. The results showed the molecular weight distribution of organic matter extracted by centrifugation, heating and cation exchange resin (CER) was similar, while the EPS extracted by centrifugation (Control) and CER had similar fluorescent organic matter. The protein secondary structures of extracted EPS by the four methods were different. The similarities of protein secondary structures between the EPS extracted by CER with the Control were the highest among the four extracted EPS. Although the EPS yield extracted by formaldehyde + NaOH method were the highest, its protein secondary structures had the lowest similarity with those extracted by the Control. Additionally, the effects of centrifugation and CER extraction on the secondary structures of bovine serum albumin were also lower than that of other extraction processes. CER enables the second maximum extraction of EPS and maximum retention of the original secondary structure of proteins.

In-vitro phagocytosis and intracellular killing of Pasteurella multocida B:2 by phagocytic cells of buffaloes

Pasteurella multocida B:2 is a Gram-negative organism causing haemorrhagic septicaemia (HS) in buffaloes. It causes severe pulmonary infection, leading to infiltration of numerous macrophages and neutrophils. Despite the inflammatory response, buffaloes succumb to HS. This study aims to evaluate the in-vitro efficacy of macrophages and neutrophils of buffalo following exposure to P. multocida B:2. In-vitro infections were done using 10⁷ cfu/ml of P. multocida B:2 for Group 1, Escherichia coli for Group 2 and Mannhaemia haemolytica A:2 for Group 3 cells. The inoculated cell cultures were harvested at 0, 30, 60 and 120 min post-exposure and the phagocytic, killing and cell death rates were determined. Both phagocytosis and killing rates of all bacteria increased over time. Phagocytosis involved between 71% and 73% neutrophils and between 60% and 64% macrophages at 120 min. Killing rate of all bacteria involved between 76% and 79% for neutrophils and between 70% and 74% for macrophages at 120 min. Death rate of neutrophils ranged between 67% in Group 3, and 88% in Group 1 at 120 min, significantly (p < 0.05) higher than Group 3 but insignificant (p > 0.05) than Group 2. Similar pattern was observed for death rate of macrophages. The phagocytosis and killing rates of P. multocida B:2 were similar to other bacterial species used in this study but more neutrophils and macrophages were dead following infection by P. multocida B:2 than M. haemolytica A:2.

Global Gene Networks in 3D4/31 Porcine Alveolar Macrophages Treated with Antigenic Epitopes of Actinobacillus pleuropneumoniae ApxIA, IIA, and IVA

Actinobacillus pleuropneumoniae (App) is the causative agent of porcine pleuropneumonia. Although App produces several virulence factors, Apx toxins, the primary App virulence factors, have been the focus of numerous studies. However, the host response against the Apx toxins has not been elucidated at the transcriptomic level. Therefore, in this study, we examined the response of an immortalized porcine alveolar macrophage cell line (IPAM 3D4/31) to four antigenic epitopes of the App exotoxins, ApxIA, IIA and IVA. The antigenic epitopes of the Apx toxins (ApxIA Ct, ApxIIA Nt, ApxIVA C1 and ApxIV C2) were determined by an in-silico antigenicity prediction analysis. Gene expression in IPAMs was analyzed by RNA-Seq after treatment with the four proteins for 24 h. A total of 15,269 DEGs were observed to be associated with cellular and metabolic processes in the GO category Biological Process and nuclear receptors and apoptosis signaling in IPA analyses. These DEGs were also related to M2 macrophage polarization and apoptosis in IPAMs. These host transcriptional analyses present novel global gene networks of the host response to treatment with Apx toxins.

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.

Cellular and compositional insight into the sludge dewatering process using enzyme treatment

Removal of intracellular water in microbial cells remains a key issue for sludge disposal, and here, a novel method of enzymatic treatment with two enzymes, lysozyme and protease, was employed. Total internal reflection fluorescence microscope (TIRF) was applied to image the bacteria in sludge and quantify the evolution of sludge bacteria for the first time. The ratio of dead/live bacterial cells was always higher in the presence of lysozyme than in the presence of protease, indicating that lysozyme has higher activity in inducing bacterial cell degradation and releasing intracellular water. The compositions of extracellular polymeric substances (EPS) were further measured, and the results show that the dewatering performance of sludge is correlated both to the release of cell contents and the variations in EPS composition during cell degradation. Moreover, kinetic analysis demonstrated that the enzyme-catalyzed reaction was substantially completed within 1 h, i.e., the reaction was quite rapid during the first 1 h, and thereafter, it gradually reduced to stability. The mechanism of enzymatic treatment of sludge explored in this study thus not only enhanced the understanding of sludge deep dewatering but also provided significant methodological clues for the disposal of sludge.

Influence of Zn(II) stress-induction on component variation and sorption performance of extracellular polymeric substances (EPS) from Bacillus vallismortis

Bacillus vallismortis (B. vallismortis), an aerobic heterotrophic bacteria, was screened in a laboratory pilot study, to assess the interaction between the heavy metal Zn(II) and extracellular polymeric substances (EPS). The influence of Zn(II) stress on EPS production, component variation, and sorption performance, was investigated. The characteristics of B. vallismortis EPS formed under stress were analyzed using FTIR, 3D-EEM and XPS. EPS was used as an adsorbent and the adsorption capacity and adsorption behavior of EPS formed with and without Zn(II) stress, were compared and assessed. Results showed that the production of polysaccharides and proteins, the main components of EPS, were promoted under Zn(II) stress. The types of EPS functional groups observed remained the same with and without heavy metal stress, but their concentrations were increased. Due to stress-induction, the adsorption capacity of Zn-EPS was significantly enhanced compared with the control-EPS. Specific EPS produced by B. vallismortis in the presence of Zn(II) stress, could have a wide range of potential applications, allowing optimization and improvement of the capacity of EPS to remove heavy metals from effluent.

Anaerobic accumulation of short-chain fatty acids from algae enhanced by damaging cell structure and promoting hydrolase activity

Short-chain fatty acid (SCFAs) produced from harvested algae by anaerobic fermentation with uncontrolled pH was limited due to the solid cell structure of algae. This study, therefore, was undertaken to enhance the generation of SCFAs from algae by controlling the fermentation pH. pH influenced not only the total SCFAs production, but the percentage of individual SCFA. The maximal yield of SCFAs occurred at pH 10.0 and fermentation time of 6 d (3161 mg COD/L), which mainly contained acetic and iso-valeric acids and was nearly eight times that at uncontrolled pH (392 mg COD/L). Mechanism exploration revealed at alkaline pH, especially at pH 10.0, not only the cell structure of algae was damaged effectively, but also activities and relative quantification of hydrolases as well as the abundance of microorganisms responsible for organics hydrolysis and SCFAs production were improved. Also, the released microcystins from algae were removed efficiently during alkaline anaerobic fermentation.

Successful sperm cryopreservation of the brown-marbled grouper, Epinephelus fuscoguttatus using propylene glycol as cryoprotectant

This study developed the cryopreservation of brown-marbled grouper spermatozoa for practical application. We examined 32 cryodiluents, developed from four types of cryoprotectants [propylene glycol (PG), dimethyl-sulphoxide (Me₂SO), dimethyl-acetamide (DMA) and ethylene glycol (EG)] at four concentrations of 5, 10, 15 and 20% in combination with two extenders [Fetal bovine serum (FBS) and artificial seminal plasma (ASP). Cooling rates were examined by adjusting the height of straws (2.5-12.5 cm) from the liquid nitrogen (LN) vapor and cooled for 5 min before immersion into LN. DNA laddering was used to detect DNA damage in cryopreserved sperm. In fertilization trials, 0.5 g of eggs was mixed with cryopreserved sperm stored for 30 days in LN. The best motility of post-thaw sperm was achieved using 15% PG + 85% FBS (76.7 ± 8.8%); 10% PG + 90% FBS was also effective as cryodiluent. Generally, FBS gave better post-thaw motility compared to ASP. The optimum cooling rate was at 17.6 °C min^-1 obtained by freezing at the height of 7.5 cm surface of LN. The results obtained showed that cryopreserved sperm of brown-marbled grouper suffered slight DNA fragmentation, which resulted in significantly lower motility. However, the fertilization (90.9 ± 0.5%), hatching (64.5 ± 4.1%) and deformity rates (3.8 ± 0.2%) obtained from cryopreserved sperm showed no significant difference with fresh sperm. These findings show that the developed protocol for cryopreservation of brown-marbled grouper sperm was viable and will be useful for successful breeding and seed production of brown-marbled grouper.

Determination of the profile of DO and its mass transferring coefficient in a biofilm reactor packed with semi-suspended bio-carriers

The work aims at illustrating the profile of DO and its mass transferring process in a biofilm reactor packed with a novel semi-suspended bio-carrier, and further revealing the main factors that influence the mass transferring coefficient of DO within the biofilm. Results showed that the biofilm was very easy to attach and grow on the semi-suspended bio-carrier, which obviously changed the DO profile inside and outside the biofilm. The semi-suspended bio-carrier caused three different mass transfer zones occurring in the bioreactor, including the zones of bulk solution, boundary layer and biofilm, in which, the boundary layer zone had an obvious higher mass transfer resistance. Increasing the aeration rate might improve the hydrodynamic conditions in the bioreactor and accelerate the mass transfer of DO, but it also detached the biofilm from the surface of bio-carrier, which reduced the consumption of DO, and accordingly, decreased the DO gradient in the bioreactor.

Interaction of Pb(II) and biofilm associated extracellular polymeric substances of a marine bacterium Pseudomonas pseudoalcaligenes NP103

Three-dimensional excitation-emission matrix (3D EEM) fluorescence spectroscopy and attenuated total reflectance fourier-transformed infrared spectroscopy (ATR-FTIR) was used to evaluate the interaction of biofilm associated extracellular polymeric substances (EPS) of a marine bacterium Pseudomonas pseudoalcaligenes NP103 with lead [Pb(II)]. EEM fluorescence spectroscopic analysis revealed the presence of one protein-like fluorophore in the EPS of P. pseudoalcaligenes NP103. Stern-Volmer equation indicated the existence of only one binding site (n=0.789) in the EPS of P. pseudoalcaligenes NP103. The interaction of Pb(II) with EPS was spontaneous at room temperature (∆G=-2.78kJ/K/mol) having binding constant (K_b) of 2.59M^-1. ATR-FTIR analysis asserted the involvement of various functional groups such as sulphydryl, phosphate and hydroxyl and amide groups of protein in Pb(II) binding. Scanning electron microscopy (SEM) and fluorescence microscopy analysis displayed reduced growth of biofilm with altered surface topology in Pb(II) supplemented medium. Energy dispersive X-ray spectroscopy (EDX) analysis revealed the entrapment of Pb in the EPS. Uronic acid, a characteristic functional group of biofilm, was observed in ¹H NMR spectroscopy. The findings suggest that biofilm associated EPS are perfect organic ligands for Pb(II) complexation and may significantly augment the bioavailability of Pb(II) in the metal contaminated environment for subsequent sequestration.

Evaluation of sludge reduction of three metabolic uncouplers in laboratory-scale anaerobic-anoxic-oxic process

To evaluate the sludge reduction of three metabolic uncouplers (3,3',4',5-tetrachlorosalicylanilide (TCS), 2,4-dichlorophenol (DCP), and tetrakis (hydroxymethyl) phosphonium sulfate (THPS)), we conducted continuous experiments on laboratory-scale anaerobic-anoxic-oxic processes. The three metabolic uncouplers were separately added in each oxic tank of the three systems, and a system without uncoupler addition was used as control. During the 85-day operation, sludge production and observed growth yields decreased to 38.6% and 16.98%, 43.4% and 17.55%, and 39.3% and 17.04% by the addition of TCS, DCP, and THPS, respectively. The addition of metabolic uncouplers slightly reduced the wastewater treatment efficiencies of the system (about 1.1-8.7%) and increased sludge SVIs (about 69.9-80.6%). Meanwhile, the differences among three metabolic uncouplers were little. Besides metabolic uncoupling and maintenance metabolism, which exist in the TCS- and DCP-added systems, lysis-cryptic growth also exists in the THPS-added system.

Evaluation of the microbial cell structure damages in alkaline pretreatment of waste activated sludge

This study investigated the damages of microbial cell structures, as well as the relationships between these damages and the release of cellular organic matter in the pretreatment of waste activated sludge (WAS) by using alkaline pretreatment as model. In the alkaline pretreatment of WAS, the most damage of bound extracellular polymeric substances (EPS), cell walls, cell membranes, and cell nuclei occurred at pH 11.5-12.0 (46.2%), pH 11.0-11.5 (27.3%), pH 9.0-10.0 (34.2%), and pH 11.5-12.0 (44.4%), respectively. The damage percentages of these cell structures in the pH stabilization stage were low because most of the damages occurred when the pH increased. The structural integrities of sludge microorganisms were all damaged in the pH increase stage. The damages of EPS, cell walls, and cell membranes were significantly correlated with the release of cellular organic matter, and these damages were necessary to release the cellular matter in WAS.

Extracellular polymeric substances govern the development of biofilm and mass transfer of polycyclic aromatic hydrocarbons for improved biodegradation

The hypothesis that extracellular polymeric substances (EPS) affect the formation of biofilms for subsequent enhanced biodegradation of polycyclic aromatic hydrocarbons was tested. Controlled formation of biofilms on humin particles and biodegradation of phenanthrene and pyrene were performed with bacteria and EPS-extracted bacteria of Micrococcus sp. PHE9 and Mycobacterium sp. NJS-P. Bacteria without EPS extraction developed biofilms on humin, in contrast the EPS-extracted bacteria could not attach to humin particles. In the subsequent biodegradation of phenanthrene and pyrene, the biodegradation rates by biofilms were significantly higher than those of EPS-extracted bacteria. Although, both the biofilms and EPS-extracted bacteria showed increases in EPS contents, only the EPS contents in biofilms displayed significant correlations with the biodegradation efficiencies of phenanthrene and pyrene. It is proposed that the bacterial-produced EPS was a key factor to mediate bacterial attachment to other surfaces and develop biofilms, thereby increasing the bioavailability of poorly soluble PAH for enhanced biodegradation.

Acylation Enhances, but Is Not Required for, the Cytotoxic Activity of Mannheimia haemolytica Leukotoxin in Bighorn Sheep

Mannheimia haemolytica causes pneumonia in domestic and wild ruminants. Leukotoxin (Lkt) is the most important virulence factor of the bacterium. It is encoded within the four-gene lktCABD operon: lktA encodes the structural protoxin, and lktC encodes a trans-acylase that adds fatty acid chains to internal lysine residues in the protoxin, which is then secreted from the cell by a type 1 secretion system apparatus encoded by lktB and lktD. It has been reported that LktC-mediated acylation is necessary for the biological effects of the toxin. However, an LktC mutant that we developed previously was only partially attenuated in its virulence for cattle. The objective of this study was to elucidate the role of LktC-mediated acylation in Lkt-induced cytotoxicity. We performed this study in bighorn sheep (Ovis canadensis) (BHS), since they are highly susceptible to M. haemolytica infection. The LktC mutant caused fatal pneumonia in 40% of inoculated BHS. On necropsy, a large number of necrotic polymorphonuclear leukocytes (PMNs) were observed in the lungs. Lkt from the mutant was cytotoxic to BHS PMNs in an in vitro cytotoxicity assay. Flow cytometric analysis of mutant Lkt-treated PMNs revealed the induction of necrosis. Scanning electron microscopic analysis revealed the presence of pores and blebs on mutant-Lkt-treated PMNs. Mass spectrometric analysis confirmed that the mutant secreted an unacylated Lkt. Taken together, these results suggest that acylation is not necessary for the cytotoxic activity of M. haemolytica Lkt but that it enhances the potency of the toxin.

Effect of short-time aerobic digestion on bioflocculation of extracellular polymeric substances from waste activated sludge

The effect of short-time aerobic digestion on bioflocculation of extracellular polymeric substances (EPSs) from waste activated sludge (WAS) was investigated. Bioflocculation of the EPS was found to be enhanced by 2∼6 h of WAS aerobic digestion under the conditions of natural sludge pH (about 7), high sludge concentration by gravity thickening, and dissolved oxygen of about 2 mg/L. With the same EPS extraction method, the total suspended solid content reduction of 0.20 and 0.36 g/L and the volatile suspended solid content reduction of 0.19 and 0.26 g/L were found for the WAS samples before and after aerobic digestion of 4 h. It indicates that more EPS is produced by short-time aerobic digestion of WAS. The scanning electron microscopy images of the WAS samples before and after aerobic digestion of 4 h showed that more EPS appeared on the surface of zoogloea by aerobic digestion, which reconfirmed that WAS aerobic digestion induced abundant formation of EPS. By WAS aerobic digestion, the flocculating rate of the EPS showed about 31 % growth, almost consistent with the growth of its yield (about 34 %). The EPSs obtained before and after the aerobic digestion presented nearly the same components, structures, and Fourier transform infrared spectra. These results revealed that short-time aerobic digestion of WAS enhanced the flocculation of the EPS by promoting its production.

Effect of citric acid induced deflocculation on the ultrasonic pretreatment efficiency of dairy waste activated sludge

In this investigation, the application of citric acid was explored for the removal of extracellular polymeric substance (EPS) from waste activated sludge (WAS), followed by ultrasonic pretreatment, which enhanced the subsequent anaerobic biodegradability. EPS was removed with 0.05g/g SS of citric acid. The chemical oxygen demand (COD) solubilization and suspended solids (SS) reduction that occurred for specific energy input of 171.9kJ/kg TS, in deflocculated (EPS removed and ultrasonically pretreated) sludges were found to be 22.70% and 20.28% and was comparatively higher, than the flocculated (with EPS and ultrasonically pretreated). The biogas yield potential of flocculated and deflocculated sludges (specific energy input - 171.9kJ/kgTS) was found to be 0.212L/(gVS) and 0.435L/(gVS), respectively. Accordingly, the deflocculation and ultrasonic pretreatment improved the anaerobic biodegradability efficiently. Thus, this chemo mediated sonic pretreatment is an effective method for enhancing biodegradability and improving clean energy generation from WAS.

Optimization for extracellular polymeric substances extraction of microbial aggregates

The extracellular polymeric substances (EPS) are important macromolecular components in microbial aggregates. The three EPS extraction methods - ultrasound + cation exchange resins (CER) + sulfide, ultrasound + formamide + NaOH, and ultrasound + heat - were investigated in the study, and the component differences of extracted EPS from the loose flocs and dense aerobic granules were compared using chemical analysis and three-dimensional excitation-emission matrix (3D-EEM). Results showed that the contents of EPS were extracted effectively by ultrasound + formamide + NaOH and ultrasound + heat methods, and the ultrasound + CER + sulfide method did not extract the polysaccharides (PS) or protein (PN) contents from the sludge samples. The 3D-EEM analysis indicated that the nature of peak B/D, peak C/E/F, and peak A/G were attributed to PN-like, humic acid-like and fulvic acid-like fluorophores. All fluorophores can be detected from the EPS extracted through the ultrasound + heat method. Hopefully this will provide more information about the EPS interaction mechanism of microbial aggregates.

Hydrothermal treatment coupled with mechanical expression at increased temperature for excess sludge dewatering: the dewatering performance and the characteristics of products

Hydrothermal treatment coupled with mechanical expression at increased temperature in two separate cells respectively is effective for the dewatering of excess sludge with low energy consumption. The objectives of this study were to evaluate the dewatering performance and the characteristics of obtained products (hydrothermal sludge, hydrochar and filtrate). The results showed that harsher hydrothermal treatment (temperature from 120 to 210 °C and residence time from 10 to 90 min) led to greater water removal (from 7.44 to 96.64% reduction of total water) and mechanical pressure became less significant as it increased. The whole expression stage was completely described by the modified Terzaghi-Voigt rheological model. The role of tertiary consolidation stage in the water removal was reduced with hydrothermal treatment being stronger. The hydrothermal treatment is mainly a devolatilization process. The observed changes in H/C and O/C for hydrothermal sludge suggested dehydration was the major reaction mechanism and decarboxylation only occurred significantly at higher temperature. The higher heating value correlated well with carbon content of sludge, which was increased by 4.8% for hydrothermal sludge at 210 °C for 60 min and significantly decreased by 15.4% for hydrochar after 6.0 MPa for 20 min. The solubilization and decomposition of proteins, polysaccharides and DNA were determined to be temperature and residence time dependent. The improvement of dewaterability was closely correlated to the variation of these biopolymers. The filtrates collected above 150 °C were found to be acidic. The increase of humic substances and the melanoidins formed by Maillard reaction were largely responsible for the filtrate color.