Superior dimethyl disulfide degradation in a microbial fuel cell: Extracellular electron transfer and hybrid metabolism pathways

Unveiling the mechanism of microbial nitrogen conversion by acclimating bioanode potential for enhancing ammonia removal and reducing N2O emission

The biodegradation mechanism of enhancing ammonia removal and reducing N2O emission by acclimating bioanode potential in bioelectrochemical systems (BES) was studied in this work. The BES was started up and optimized with different parameters (i.e., aeration volume, external resistance, and pH value). The cyclic voltammetry was then performed to determine the potential range for acclimating bioanode, suggesting that potentials of -0.3, -0.1, 0.1, 0.2, and 0.3 V were suitable for acclimation. The experimental results indicated that optimum total nitrogen removal was achieved at potential of 0.1 V with a removal efficiency of 83.7 %, which was 1.6 times higher than that of the control group, while the corresponding N2O emission of 1.3 mg-N/L was detected which reduced 2.8 times. The microbial community analysis indicated that the dominant genera for enhancing nitrogen conversion were Sphaerocheata, Petrimonas, and Lentimicrobium. The electrochemical tests suggested that potential acclimation could simultaneously enhance direct electron transfer and mediated electron transfer (MET), thereby increasing extracellular electron transfer, in which the proportion of MET process mediated by riboflavin played a decisive role. Meanwhile, the intracellular electron transfer process was also strengthened by the increase of the related enzyme activity and the corresponding electron transport system activity increased 3.4 times. Additionally, nitrogen conversion pathways were proposed, indicating that potential acclimation could regulate the ammonia degradation pathway, and reduce the intermediates accumulation. These findings provide new understanding of the nitrogen conversion mechanisms in BES for ammonia removal by acclimating bioanode potential.

Electrode functional microorganisms in bioelectrochemical systems and its regulation: A review

Bioelectrochemical systems (BES) as environmental remediation biotechnologies have boomed in the last two decades. Although BESs combined technologies with electro-chemistry, -biology, and -physics, microorganisms and biofilms remain at their core. In this review, various functional microorganisms in BESs for CO2 reduction, dehalogenation, nitrate, phosphate, and sulfate reduction, metal removal, and volatile organic compound oxidation are summarized and compared in detail. Moreover, interrelationship regulation approaches for functional microorganisms and methods for electroactive biofilm development, such as targeted electrode surface modification, chemical treatment, physical revealing, biological optimization, and genetic programming are pointed out. This review provides promising guidance and suggestions for the selection of microbial inoculants and provides an analysis of the role of individual microorganisms in mixed microbial communities and its metabolisms.

Characterization of three novel dimethyl disulfide degrading bacteria and their potential degradation pathways

Dimethyl disulfide (DMDS) is an odor compound characterized by the lowest olfactory threshold and high toxicity. It is indispensable to explore the bacteria with high resistance and degradation efficiency to DMDS. Acinetobacter lwoffii, Pseudomonas mendocina, and Myroides odoratus were isolated from kitchen waste. After 6 days of individual treatment, the removal rates were 34.22 %, 40.95 %, and 41.94 % respectively. The DMDS metabolic pathways based on metagenomic assays were discovered to be incomplete due to the insufficient annotation of some key genes in the current database. Following 3 days of treatment with bacterial consortia at ratios of 5:1 for A. lwoffii C2/ M. odoratus C7 and 1:1:1 for the three strains achieved 100 % DMDS removal. Additionally, the consortia reduced hydrogen sulfide (H2S) and dimethyl sulfide (DMS).This discovery broadens the spectrum of bacteria exhibiting high tolerance and efficient degradation of DMDS, with significant implications for DMDS removal and odor treatment.

Electro-stimulated biodegradation of dimethyl disulfide: Insights from biofilm spatial structure and key functional genes

As a typical sulfur-containing volatile organic compound, dimethyl disulfide (DMDS) is known for its high toxicity and resistance to degradation, necessitating efficient control in environmental media. To address the limitations of biological treatment in degradation capacity, this study employs electro-stimulation to promote DMDS elimination by a porous polyaniline@carbon nanotube bioanode developed on graphite sheet (PANI@CNT/GS). Compared with the unmodified GS bioanode, the PANI@CNT/GS bioanode demonstrates significant advantages in biofilm activity, redox property, and DMDS degradation efficiency. Kinetics analysis shows that the maximum degradation rate of the PANI@CNT/GS bioanode was 0.60 mM h-1, which is 1.36 times higher than that of the control. Characterization results reveal that the highly active biofilms in PANI@CNT/GS bioanode possess 1.40 times the amount of living cells and a 12.5% increase in thickness, contributing to the notable enhancement in DMDS degradation capacity. Additionally, functional gene annotation indicates that the PANI@CNT/GS electrode facilitates the motility and activity of microbial cells and enriches the genes encoding key enzymes involved in DMDS metabolism. This work validates the feasibility of electro-stimulation for enhancing DMDS degradation and further provides in-depth insights into the process intensification mechanism from the perspectives of biofilm spatial structure and key functional genes.

Analysis of the Urine Volatilome of COVID-19 Patients and the Possible Metabolic Alterations Produced by the Disease

Alterations in metabolism caused by SARS-CoV-2 infection have been highlighted in various investigations and have been used to search for biomarkers in different biological matrices. However, the selected biomarkers vary greatly across studies. Our objective is to provide a robust selection of biomarkers, including results from different sample treatments in the analysis of volatile organic compounds (VOCs) present in urine samples from patients with COVID-19. Between September 2021 and May 2022, urine samples were collected from 35 hospitalized COVID-19 patients and 32 healthy controls. The samples were analyzed by headspace (HS) solid phase microextraction (SPME) coupled to gas chromatography-mass spectrometry (GC-MS). Analyses were conducted on untreated urine samples and on samples that underwent specific pretreatments: lyophilization and treatment with sulfuric acid. Partial Least Squares Linear Discriminant Analysis (PLS-LDA) and Subwindow Permutation Analysis (SPA) models were established to distinguish patterns between COVID-19 patients and healthy controls. The results identify compounds that are present in different proportions in urine samples from COVID-19 patients compared to those from healthy individuals. Analysis of urine samples using HS-SPME-GC-MS reveals differences between COVID-19 patients and healthy individuals. These differences are more pronounced when methods that enhance VOC formation are used. However, these pretreatments can cause reactions between sample components, creating additional products or removing compounds, so biomarker selection could be altered. Therefore, using a combination of methods may be more informative when evaluating metabolic alterations caused by viral infections and would allow for a better selection of biomarkers.

Biofilm metagenomic characteristics behind high coulombic efficiency for propanethiol deodorization in two-phase partitioning microbial fuel cell

Hydrophobic volatile organic sulfur compounds (VOSCs) are frequently found during sewage treatment, and their effective management is crucial for reducing malodorous complaints. Microbial fuel cells (MFC) are effective for both VOSCs abatement and energy recovery. However, the performance of MFC on VOSCs remains limited by the mass transfer efficiency of MFC in aqueous media. Inspired by two-phase partitioning biotechnology, silicone oil was introduced for the first time into MFC as a non-aqueous phase (NAP) medium to construct two-phase partitioning microbial fuel cell (TPPMFC) and augment the mass transfer of target VOSCs of propanethiol (PT) in the liquid phase. The PT removal efficiency within 32 h increased by 11-20% compared with that of single-phase MFC, and the coulombic efficiency of TPPMFC (11.01%) was 4.32-2.68 times that of single-phase MFC owing to the fact that highly active desulfurization and thiol-degrading bacteria (e.g., Pseudomonas, Achromobacter) were attached to the silicone oil surface, whereas sulfur-oxidizing bacteria (e.g., Thiobacillus, Commonas, Ottowia) were dominant on the anodic biofilm. The outer membrane cytochrome-c content and NADH dehydrogenase activity improved by 4.15 and 3.36 times in the TPPMFC, respectively. The results of metagenomics by KEGG and COG confirmed that the metabolism of PT in TPPMFC was comprehensive, and that the addition of a NAP upregulates the expression of genes related to sulfur metabolism, energy generation, and amino acid synthesis. This finding indicates that the NAP assisted bioelectrochemical systems would be promising to solve mass-transfer restrictions in low solubility contaminates removal.

Exploring ozone formation rules and concentration response to the change of precursors based on artificial neural network simulation in a typical industrial park

Industrial parks have more complex O3 formation mechanisms due to a higher concentration and more dense emission of precursors. This study establishes an artificial neural network (ANN) model with good performance by expanding the moment and concentration changes of pollutants into general variables of meteorological factors and concentrations of pollutants. Finally, the O3 formation rules and concentration response to the changes of volatile organic compounds (VOCs) and nitrogen oxides (NOx) was explored. The results showed that the studied area belonged to the NOx-sensitive regime and the sensitivity was strongly affected by relative humidity (RH) and pressure (P). The concentration of O3 tends to decrease with a higher P, lower temperature (Temp), and medium to low RH when nitric oxide (NO) is added. Conversely, at medium P, high Temp, and high RH, the addition of nitrogen dioxide (NO2) leads to a larger decrease capacity in O3 concentration. More importantly, there is a local reachable maximum incremental reactivity (MIRL) at each certain VOCs concentration level which linearly increased with VOCs. The general maximum incremental reactivity (MIR) may lead to a significant overestimation of the attainable O3 concentration in NOx-sensitive regimes. The results can significantly support the local management strategies for O3 and the precursors control.