Biochar as a partner of plants and beneficial microorganisms to assist in-situ bioremediation of heavy metal contaminated soil.

Synergistic remediation of heavy metal (HM) contaminated soil using beneficial microorganisms (BM) and plants is a common and effective in situ bioremediation method. However, the shortcomings of this approach are the low colonisation of BM under high levels of heavy metal stress (HMS) and the poor state of plant growth. Previous studies have overlooked the potential of biochar to mitigate the above problems and aid in-situ remediation. Therefore, this paper describes the characteristics and physicochemical properties of biochar. It is proposed that biochar enhances plant resistance to HMS and aids in situ bioremediation by increasing colonisation of BM and HM stability. On this basis, the paper focuses on the following possible mechanisms: specific biochar-derived organic matter regulates the transport of HMs in plants and promotes mycorrhizal colonisation via the abscisic acid signalling pathway and the karrikin signalling pathway; promotes the growth-promoting pathway of indole-3-acetic acid and increases expression of the nodule-initiating gene NIN; improvement of soil HM stability by ion exchange, electrostatic adsorption, redox and complex precipitation mechanisms. And this paper summarizes guidelines on how to use biochar-assisted remediation based on current research for reference. Finally, the paper identifies research gaps in biochar in the direction of promoting beneficial microbial symbiotic mechanisms, recognition and function of organic molecules, and factors affecting practical applications.

Enhanced treatment of synthetic wastewater by bioaugmentation with a constructed consortium.

Bioaugmentation by adding well-functioning mixed microorganism consortia represents a potentially useful approach to improve contaminant removal in wastewater treatment plants (WWTPs). However, unfavorable environmental conditions (i.e., low temperatures) can severely inhibit microbial activity, drawing our attention to constructing cold-tolerant microorganism preparations and investigating their availability in practical applications. Here we screened four in situ functional isolates from the activated sludge of secondary sedimentation tanks in WWTPs to construct a psychrophilic microbial consortium, which was used to perform bioaugmentation for enhanced removal of nitrogen and phosphorus under low temperatures. The consortium was established by cocultivation of four isolates, characterized by 16 S rRNA as the COD-degrading bacterium Aeromonas sp. Z3, aerobic denitrifying bacterium Acinetobacter sp. HF9, nitrifying bacterium Klebsiella sp. X8, and polyphosphate-accumulating bacterium Pseudomonas sp. PC5 respectively. The microorganism preparation was composed of Z3, HF9, X8, and PC5 under the ratio of 1: 1: 3: 1, which can exert optimal pollutant removal under the conditions of 12 °C, 6.0-9.0 pH, 120-200 r‧min-1, and a dosage of 5% (V/V). A 30-day continuous operation of the bioaugmented and control sequencing batch reactors (SBRs) was investigated, and the bioaugmented SBR showed a shorter start-up stage and a more stable operating situation. Compared to the control SBR, the COD, NH4+-N, TN, and TP removal efficiency of the bioaugmented SBR increased by an average of 7.95%, 9.05%, 9.54%, and 7.45% respectively. The analysis of the microbial community revealed that the introduced isolates were dominant in the activated sludge and that functional taxa such as Proteobacteria, Bacteroidota, and Actinobacteria were further enriched after a period of bioaugmentation. The study provides some basis and guidance for the practical application of how to strengthen the stable operation of WWTPs under low temperatures.

Application of molecular dynamics simulation for exploring the roles of plant biomolecules in promoting environmental health.

Understanding the dynamic changes of plant biomolecules is vital for exploring their mechanisms in the environment. Molecular dynamics (MD) simulation has been widely used to study structural evolution and corresponding properties of plant biomolecules at the microscopic scale. Here, this review (i) outlines structural properties of plant biomolecules, and the crucial role of MD simulation in advancing studies of the biomolecules; (ii) describes the development of MD simulation in plant biomolecules, determinants of simulation, and analysis parameters; (iii) introduces the applications of MD simulation in plant biomolecules, including the response of the biomolecules to multiple stresses, their roles in corrosive environments, and their contributions in improving environmental health; (iv) reviews techniques integrated with MD simulation, such as molecular biology, quantum mechanics, molecular docking, and machine learning modeling, which bridge gaps in MD simulation. Finally, we make suggestions on determination of force field types, investigation of plant biomolecule mechanisms, and use of MD simulation in combination with other techniques. This review provides comprehensive summaries of the mechanisms of plant biomolecules in the environment revealed by MD simulation and validates it as an applicable tool for bridging gaps between macroscopic and microscopic behavior, providing insights into the wide application of MD simulation in plant biomolecules.

Enhanced visible light photo-Fenton catalysis by lanthanum-doping BiFeO3 for norfloxacin degradation.

Efficient photo-Fenton removal of antibiotic effluent is a widely followed and significant attempt to deal with the growing environmental pollution. In this study, BiFeO3 and lanthanum doped BiFeO3 catalysts were synthesized via one-step hydrothermal method as hydrogen peroxide activator for mineralization of norfloxacin (NOR). Various characterization measurements were used to verify La was successfully doped into the lattice of perovskite and investigated the effect of La doping molar ratio on BiFeO3 through the characterization of the morphology and physicochemical properties. The degradation experiment and reaction rate constants showed that the La-doped BiFeO3 particle exhibited superior photo-Fenton catalytic performance to undoped BiFeO3. Especially, the degradation efficiency of 15% La-doped BiFeO3 could reach up to 84.94%. And the first order kinetic constant of optimized conditions was 0.01638 min-1, which was about 6.9 times than that of undoped BiFeO3.The influence of pH, oxidizer content and catalyst dosage in photo-Fenton reaction were investigated detailedly. Besides, the synthetic catalyst possessed favorable stability and reusability with little metal leaching after many cycles of use. Radical scavenger experiments and electron spin resonance tests were carried out to conclude that the ·OH and holes were regarded as the dominate active species in the catalytic process. The narrow band gap and excellent electron transfer efficiency were the key factors for La-doped BiFeO3 to have high catalytic efficiency in the photo-Fenton system. Current works demonstrated the great promise of La-doped BiFeO3 in the elimination of antibiotic organics.

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 ß-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.

Harnessing Paenarthrobacter ureafaciens YL1 and Pseudomonas koreensis YL2 Interactions to Improve Degradation of Sulfamethoxazole.

Sulfamethoxazole (SMX) is a widespread and persistent pollutant in the environment. Although the screening and analysis of SMX-degrading bacteria have been documented, the interaction mechanisms of functional microorganisms are still poorly understood. This study constructed a consortium with strain YL1 and YL2 supplied with SMX as the sole carbon and energy source. The coexisting mechanism and the removal of SMX of the consortium were investigated. The total oxidizable carbon (TOC) removal rate of the combined bacterial system was 38.94% compared to 29.45% for the single bacterial system at the same biomass. The mixed bacterial consortium was able to resist SMX at concentrations up to 400 mg/L and maintained a stable microbial structure at different culture conditions. The optimum conditions found for SMX degradation were 30 °C, pH 7.0, a shaking speed of 160 r·min-1, and an initial SMX concentration of 200 mg·L-1. The degradation of SMX was accelerated by the addition of YL2 for its ability to metabolize the key intermediate, 4-aminophenol. The removal rate of 4-aminophenol by strain YL2 reached 19.54% after 5 days. Genome analysis revealed that adding riboflavin and enhancing the reducing capacity might contribute to the degradation of SMX. These results indicated that it is important for the bioremediation of antibiotic-contaminated aquatic systems to understand the metabolism of bacterial communities.

Direct sludge granulation by applying mycelial pellets in continuous-flow aerobic membrane bioreactor: Performance, granulation process and mechanism.

This study provides a sustainable manner for direct cultivation of aerobic granular sludge (AGS) by addition of mycelial pellets (MPs) into continuous-flow aerobic MBR. The results showed that the granulation time in MPs-MBR was shortened by at least 65 days, accounting for enhanced mean size of granules (0.68-0.76 mm), increased mixed liquor suspended solids (MLSS) concentration (12.8 g/L) and improved settling ability (78.1 mL/g), in comparison with that of 0.23-0.28 mm, 9.8 g/L and 102.1 mL/g in control MBR. MPs-MBR demonstrated significant advantages in terms of COD reduction (97.0-99.1%), NH4+-N reduction (100%) and TN reduction (32.27-42.33%). MPs, extracellular polymeric substances (EPS) and filamentous bacteria acted as inducible nucleus, crosslinking matter and supporting skeleton, respectively, in favor of promoting the formation and stabilization of AGS with a four-layered structure. The relevant mechanism was underlined by rheological analysis, indicating that MPs addition enhanced non-Newtonian flow characteristics and network structure of sludge.

Xanthobacter dioxanivorans sp. nov., a 1,4-dioxane-degrading bacterium.

A Gram-stain-negative bacterium, designated as YN2T, that is capable of degrading 1,4-dioxane, was isolated from active sludge collected from a wastewater treatment plant in Harbin, PR China. Cells of strain YN2T were aerobic, motile, pleomorphic rods, mostly twisted, and contained the water-insoluble yellow zeaxanthin dirhamnoside. Strain YN2T grew at 10-40 °C (optimum, 30 °C), pH 5.0-8.0 (pH 7.0) and with 0-1 % (w/v) NaCl (0.1 %). It also could grow chemolithoautotrophically and fix N2 when no ammonium or nitrate was supplied. Phylogenetic analysis based on 16S rRNA gene sequences revealed that strain YN2T belongs to the genus Xanthobacter and shares the highest pairwise identity with Xanthobacter autotrophicus 7cT (98.6 %) and Xanthobacter flavus 301T (98.4 %). The major respiratory quinone was ubiquinone-10. Chemotaxonomic analysis revealed that the strain possesses C16 : 0, C19 : 0 cyclo ω8c and C18 : 1 ω7c as the major fatty acids. The DNA G+C content was 67.95 mol%. Based on genome sequences, the DNA-DNA hybridization estimate values between strain YN2T and X. autotrophicus 7cT, X. flavus 301T and X. tagetidis TagT2CT (the only three species of Xanthobacter with currently available genomes) were 31.70, 31.30 and 28.50 %; average nucleotide identity values were 85.23, 84.84 and 83.59 %; average amino acid identity values were 81.24, 80.23 and 73.57 %. Based on its phylogenetic, phenotypic, and physiological characteristics, strain YN2T is considered to represent a novel species of the genus Xanthobacter, for which the name Xanthobacter dioxanivorans sp. nov. is proposed. The type strain is YN2T (=CGMCC 1.19031T=JCM 34666T).

Adaption and Degradation Strategies of Methylotrophic 1,4-Dioxane Degrading Strain Xanthobacter sp. YN2 Revealed by Transcriptome-Scale Analysis.

Biodegradation of 1,4-dioxane (dioxane) contamination has gained much attention for decades. In our previous work, we isolated a highly efficient dioxane degrader, Xanthobacter sp. YN2, but the underlying mechanisms of its extraordinary degradation performance remained unresolved. In this study, we performed a comparative transcriptome analysis of YN2 grown on dioxane and citrate to elucidate its genetic degradation mechanism and investigated the transcriptomes of different dioxane degradation stages (T0, T24, T48). We also analyzed the transcriptional response of YN2 over time during which the carbon source switched from citrate to dioxane. The results indicate that strain YN2 was a methylotroph, which provides YN2 a major advantage as a pollutant degrader. A large number of genes involved in dioxane metabolism were constitutively expressed prior to dioxane exposure. Multiple genes related to the catabolism of each intermediate were upregulated by treatment in response to dioxane. Glyoxylate metabolism was essential during dioxane degradation by YN2, and the key intermediate glyoxylate was metabolized through three routes: glyoxylate carboligase pathway, malate synthase pathway, and anaplerotic ethylmalonyl-CoA pathway. Genes related to quorum sensing and transporters were significantly upregulated during the early stages of degradation (T0, T24) prior to dioxane depletion, while the expression of genes encoding two-component systems was significantly increased at late degradation stages (T48) when total organic carbon in the culture was exhausted. This study is the first to report the participation of genes encoding glyoxalase, as well as methylotrophic genes xoxF and mox, in dioxane metabolism. The present study reveals multiple genetic and transcriptional strategies used by YN2 to rapidly increase biomass during growth on dioxane, achieve high degradation efficiency and tolerance, and adapt to dioxane exposure quickly, which provides useful information regarding the molecular basis for efficient dioxane biodegradation.

Biological mechanism of alleviating membrane biofouling by porous spherical carriers in a submerged membrane bioreactor.

In this study, porous spherical carriers were fixed around the hollow fiber membrane module to mitigate membrane biofouling. Two MBRs (R1 without carriers, R2 with carriers) were operated for 31 days under identical operating conditions to investigate the effects of the carriers on the reactor performances, the production of extracellular polymeric substances (EPS), the level of N-acyl-homoserine lactones (AHLs), and the microbial communities. The results showed that the presence of carriers in MBR was conducive to nitrogen removal and decreased the total membrane filtration resistance by about 1.7 times. Slower transmembrane pressure (TMP) rise-up, thinner bio-cakes, lower EPS production, and fewer tryptophan and aromatic proteins substances on the membrane surface were observed in R2. The polysaccharides secretion of EPS in bio-cakes was mainly regulated by C4-HSL and 3OC6-HSL in the presence of carriers. The microbial community analysis revealed that carriers addition reduced the relative abundance of EPS and AHL producing bacteria in the membrane bio-cakes and enriched the accumulation of functional bacteria conducive to nutrient removal in the mixed liquor. This study provided an in-depth understanding for the application of porous spherical carriers to alleviate membrane biofouling.

Impact of fungal pellets dosage on long-term stability of aerobic granular sludge.

The effects of fungal pellets (FPs) dosage on both structural and functional stability of aerobic granular sludge (AGS) were investigated during 200-day operation. Results showed that the AGS induced by low (a dry mass ratio of FPs to seed sludge, 30%) and high FPs dosage (60%) exhibited good morphology integrity during the entire phase of operation, while the filamentous overgrowth and AGS breakup were observed in the control reactor (0% FPs). Moreover, the granules developed at high FPs dosage demonstrated excellent nutrients removal (COD: 93%; NH4+-N: 100%; TN: 77%) and stable bioactivity with a maximum specific oxygen uptake rate (SOUR) of 52.6 ± 2.6 mg O2/(gVSS·h), a value being 12.2% and 26.7% higher than that of 30% and 0% dosage. The microbial community analysis revealed 60% FPs dosage enriched various functional bacteria involved in nutrients removal. This study suggests a sustainable strategy for improving structural and functional stability of AGS.

Degradation of 1,4-Dioxane by Xanthobacter sp. YN2.

1,4-Dioxane is a highly toxic and carcinogenic pollutant found worldwide in groundwater and soil environments. Several microorganisms have been isolated by their ability to grow on 1,4-dioxane; however, low 1,4-dioxane tolerance and slow degradation kinetics remain obstacles for their use in 1,4-dioxane bioremediation. We report here the isolation and characterization of a new strain, Xanthobacter sp. YN2, capable of highly efficient 1,4-dioxane degradation. High degradation efficiency and high tolerance to 1,4-dioxane make this new strain an ideal candidate for the biodegradation of 1,4-dioxane in various treatment facilities. The maximum degradation rate of 1,4-dioxane was found to be 1.10 mg-1,4-dioxane/h mg-protein. Furthermore, Xanthobacter sp. YN2 was shown to grow in the presence of higher than 3000 mg/L 1,4-dioxane with little to no degradation inhibition. In addition, Xanthobacter sp. YN2 could grow on and degrade 1,4-dioxane at pH ranges 5 to 8 and temperatures between 20 and 40 °C. Xanthobacter sp. YN2 was also found to be able to grow on a variety of other substrates including several analogs of 1,4-dioxane. Genome sequence analyses revealed the presence of two soluble di-iron monooxygenase (SDIMO) gene clusters, and regulation studies determined that all of the genes in these two clusters were upregulated in the presence of 1,4-dioxane. This study provides insights into the bacterial stress response and the highly efficient biodegradation of 1,4-dioxane as well as the identification of a novel Group-2 SDIMO.

Biodiversity, isolation and genome analysis of sulfamethazine-degrading bacteria using high-throughput analysis.

Sulfamethazine (SM2) is one of the sulfonamide antibiotics that is frequently detected in aquatic environment. Given the complex structure of SM2 and its potential threat to the environment, it is necessary to determine the degradation behavior of high-concentration SM2. The mechanisms of community structure and diversity of activated sludge were analyzed. A novel SM2-degrading strain YL1 was isolated which can degrade SM2 with high concentration of 100 mg L-1. Strain YL1 was identified as Paenarthrobacter ureafaciens and there was also a significant increase in the genus during acclimation. Additional SM2 metabolic mechanisms and genomic information of YL1 were analyzed for further research. The succession of the community structure also investigated the effect of SM2 on the activated sludge. This result not only advances the current understanding of microbial ecology in activated sludge, but also has practical implications for the design and operation of the environmental bioprocesses for treatment of antimicrobial-bearing waste streams.

The Addition of N-Hexanoyl-Homoserine Lactone to Improve the Microbial Flocculant Production of Agrobacterium tumefaciens Strain F2, an Exopolysaccharide Bioflocculant-Producing Bacterium.

In this study, N-hexanoyl-homoserine lactone (C6-HSL), a member of the N-acyl-homoserine lactone class of microbial quorum sensing (QS) signaling molecules, was used to improve microbial flocculant production. After exogenous C6-HSL was added, exopolysaccharide concentration of microbial flocculants was improved by 1.6-fold and flocculation rate of microbial flocculants was increased by 10 %. Fermentation conditions with added C6-HSL were further optimized through response surface methodology. The obtained optimal fermentation conditions were as follows: added C6-HSL concentration of 0.45 µM, fermentation temperature of 30.4 °C, and initial fermentation pH of 7.25. Under these optimal fermentation conditions, the resulting exopolysaccharide concentration was improved by 1.75-fold and flocculation rate was increased by 10 % compared with that of the control group. The yield of microbial flocculants was also improved by 1.75-fold. Results demonstrated that the existence of QS system in Agrobacterium tumefaciens strain F2 played the important roles in the microbial flocculant production.

Complete genome sequence of Klebsiella pneumoniae J1, a protein-based microbial flocculant-producing bacterium.

Klebsiella pneumoniae J1 is a Gram-negative strain, which belongs to a protein-based microbial flocculant-producing bacterium. However, little genetic information is known about this species. Here we carried out a whole-genome sequence analysis of this strain and report the complete genome sequence of this organism and its genetic basis for carbohydrate metabolism, capsule biosynthesis and transport system.