Environmental VOSCs--formation and degradation of dimethyl sulfide, methanethiol and related materials

Qualitative and Untargeted Volatilome Fingerprinting of Aspergillus sp. and Bulbithecium sp. by HS-SPME-GCMS and Functional Interactions

Research on fungal volatile organic compounds (VOCs) has increased worldwide in the last 10 years, but marine fungal volatilomes remain underexplored. Similarly, the hormone-signaling pathways, agronomic significance, and biocontrol potential of VOCs in plant-associated fungi make the area of research extremely promising. In the current investigation, VOCs of the isolates-Aspergillus sp. GSBT S13 and GSBT S14 from marine sediments, and Bulbithecium sp. GSBT E3 from Eucalyptus foliage were extracted using Head Space solid phase microextraction, followed by gas chromatography-mass spectrometry, identification, statistical analyses, and prediction of functions by KEGG COMPOUND and STITCH 5.0 databases. The significance of this research is fingerprinting VOCs of the isolates from distinct origins, identification of compounds using three libraries (NIST02, NIST14, and W9N11), and using bioinformatic tools to perform functional analysis. The most important findings include the identification of previously unreported compounds in fungi-1-methoxy naphthalene, diethyl phthalate, pentadecane, pristane, and nonanal; the prediction of the involvement of small molecules in the degradation of aromatic compound pathways and activation, inhibition, binding, and catalysis of metabolites with predicted protein partners. This study has ample opportunity to validate the findings and understand the mechanism or mode of action, the interspecies interactions, and the role of the metabolites in geochemical cycles.

Management of methyl mercaptan contained in waste gases - an overview

Methyl mercaptan is a typical volatile organosulfur pollutant contained in many gases emitted by urban waste treatment, various industries, natural gas handling, refining processes, and energy production. This work is a comprehensive overview of the scientific and practical aspects related to the management of methyl mercaptan pollution. The main techniques, including absorption, adsorption, oxidation, and biological treatments, are examined in detail. For each method, its capability as well as the technical advantages and drawbacks have been highlighted. The emerging methods developed for the removal of methyl mercaptan from natural gas are also reviewed. These methods are based on the catalytic conversion of CH3SH to hydrocarbons and H2S.

Plastic Litter Emits the Foraging Infochemical Dimethyl Sulfide after Submersion in Freshwater Rivers

Plastic pollution is widespread throughout aquatic environments globally, with many organisms known to interact with and ingest plastic. In marine environments, microbial biofilms that form on plastic surfaces can produce the odorous compound dimethyl sulfide (DMS), which is a known foraging cue. This has been shown to increase the ingestion of plastic by some invertebrates and therefore act as a biological factor which influences the risks of plastic to marine ecosystems. In freshwater however, the production of DMS has been largely overlooked, despite the known sensitivity of some freshwater species to this compound. To address this gap, the present study analyzed the production of DMS by biofilms which formed on low-density polyethylene and polylactic acid films after 3 and 6 weeks of submersion in either a rural or an urban United Kingdom river. Using gas chromatography-mass spectrometry, the production of DMS by these biofilms was consistently identified. The amount of DMS produced varied significantly across river locations and materials, with surfaces in the urban river generally producing a stronger signal and plastics producing up to seven times more DMS than glass control surfaces. Analysis of biofilm weight and photosynthetic pigment content indicated differences in biofilm composition across conditions and suggested that DMS production was largely driven by nonphotosynthetic taxa. For the first time this work has documented the production of DMS by plastic litter after submersion in freshwater rivers. Further work is now needed to determine if, as seen in marine systems, this production of DMS can encourage the interaction of freshwater organisms with plastic litter and therefore operate as a biological risk factor in the impacts of plastic on freshwater environments. Environ Toxicol Chem 2024;43:1485-1496. © 2024 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC.

Theoretical Insights into the Gas-Phase Oxidation of 3-Methyl-2-butene-1-thiol by the OH Radical: Thermochemical and Kinetic Analysis

3-Methyl-2-butene-1-thiol ((CH3)2C═CH-CH2-SH; MBT) is a recently identified volatile organosulfur compound emitted from Cannabis sativa and is purported to contribute to its skunky odor. To understand its environmental fate, hydroxyl radical (•OH)-mediated oxidation of MBT was conducted using high-level quantum chemical and theoretical kinetic calculations. Three stable conformers were identified for the title molecule. Abstraction and addition pathways are possible for the MBT + OH radical reaction, and thus, potential energy surfaces involving H-abstraction and •OH addition were computed at the CCSD(T)/aug-cc-pV(T+d)Z//M06-2X/aug-cc-pV(T+d)Z level of theory. The barrier height for the addition of the OH radical to a C atom of the alkene moiety, leading to the formation of a C-centered MBT-OH radical, was computed to be -4.1 kcal mol-1 below the energy of the starting MBT + OH radical-separated reactants. This reaction was found to be dominant compared to other site-specific H-abstraction and addition paths. The kinetics of all the site-specific abstraction and addition reactions associated with the most stable MBT + OH radical reaction were assessed using the MESMER kinetic code between 200 and 320 K. Further, we considered the contributions from two other conformers of MBT to the overall reaction of MBT + OH radical. The estimated global rate coefficient for the oxidation of MBT with respect to its reactions with the OH radical was found to be 6.1 × 10-11 cm3 molecule-1 s-1 at 298 K and 1 atm pressure. The thermodynamic parameters and atmospheric implications of the MBT + OH reaction are discussed.

Comprehensively assessing priority odorants emitted from swine slurry combining nontarget screening with olfactory threshold prediction

The lack of one-to-one olfactory thresholds (OTs) poses an obstacle to the comprehensive assessment of priority odorants emitted from swine slurry using mass spectrometric nontarget screening. This study screened out highly performing quantitative structure-activity relationship (QSAR) models of OT prediction to complement nontarget screening in olfactory perception evaluation. A total of 27 compounds emitted at different slurry removal frequencies were identified and quantified using gas chromatography-mass spectrometry (GC-MS), including thiirane, dimethyl trisulfide (DMTS), and dimethyl tetrasulfide (DMQS) without OT records. Ridge regression (RR, R2 = 0.77, RMSE = 0.93, MAE = 0.73) and random forest regression (RFR, R2 = 0.76, RMSE = 0.97, MAE = 0.69) rather than the commonly used principal component regression (PCR) and partial least squares regression (PLSR) were used to assign OTs and assess the contributions of emerging volatile sulfur compounds (VSCs) to the sum of odor activity value (SOAV). Priority odorants were p-cresol (25.0-58.9 %) > valeric acid (8.3-31.7 %) > isovaleric acid (6.7-19.0 %) > dimethyl disulfide (4.7-15.7 %) > methanethiol (0-13.6 %) > isobutyric acid (0-8.6 %), whereas the contributions of three emerging VSCs were below 10 %. Vital olfactory active structures were identified by QSAR models as having high molecular polarity, high hydrophilicity, high charge quantity, flexible structure, high reactivity, and a high number of sulfur atoms. This protocol can be further extended to evaluate odor pollution levels for distinct odor sources and guide the development of pertinent deodorization technologies.

Rhodobacteraceae methanethiol oxidases catalyze methanethiol degradation to produce sulfane sulfur other than hydrogen sulfide

Methanethiol (MT) is a sulfur-containing compound produced during dimethylsulfoniopropionate (DMSP) degradation by marine bacteria. The C-S bond of MT can be cleaved by methanethiol oxidases (MTOs) to release a sulfur atom. However, the cleaving process remains unclear, and the species of sulfur product is uncertain. It has long been assumed that MTOs produce hydrogen sulfide (H2S) from MT. Herein, we studied the MTOs in the Rhodobacteraceae family-whose members are important DMSP degraders ubiquitous in marine environments. We identified 57 MTOs from 1,904 Rhodobacteraceae genomes. These MTOs were grouped into two major clusters. Cluster 1 members share three conserved cysteine residues, while cluster 2 members contain one conserved cysteine residue. We examined the products of three representative MTOs both in vitro and in vivo. All of them produced sulfane sulfur other than H2S from MT. Their conserved cysteines are substrate-binding sites in which the MTO-S-S-CH3 complex is formed. This finding clarified the sulfur product of MTOs and enlightened the MTO-catalyzing process. Moreover, this study connected DMSP degradation with sulfane sulfur metabolism, filling a critical gap in the DMSP degradation pathway and representing new knowledge in the marine sulfur cycle field.

IMPORTANCE

This study overthrows a long-time assumption that methanethiol oxidases (MTOs) cleave the C-S bond of methanethiol to produce both H2S and H2O2-the former is a strong reductant and the latter is a strong oxidant. From a chemistry viewpoint, this reaction is difficult to happen. Investigations on three representative MTOs indicated that sulfane sulfur (S0) was the direct product, and no H2O2 was produced. Finally, the products of MTOs were corrected to be S0 and H2O. This finding connected dimethylsulfoniopropionate (DMSP) degradation with sulfane sulfur metabolism, filling a critical gap in the DMSP degradation pathway and representing new knowledge in the marine sulfur cycle field.

Effects of operating conditions on the in situ control of sulfur-containing odors by using a novel alternative landfill cover and its transformation mechanism

Sulfur-containing gases are main sources of landfill odors, which has become a big issue for pollution to environment and human health. Biocover is promising for treating landfill odors, with advantages of durability and environmental friendliness. In this study, charcoal sludge compost was utilized as the main effective component of a novel alternative landfill cover and the in situ control of sulfur-containing odors from municipal solid waste landfilling process was simulated under nine different operating conditions. Results showed that five sulfur-containing odors (hydrogen sulfide, H2S; methyl mercaptan, CH3SH; dimethyl sulfide, CH3SCH3; ethylmercaptan, CH3CH2SH; carbon disulfide, CS2) were monitored and removed by the biocover, with the highest removal efficiencies of 77.18% for H2S, 87.36% for CH3SH, and 92.19% for CH3SCH3 in reactor 8#, and 95.94% for CH3CH2SH and 94.44% for CS2 in reactor 3#. The orthogonal experiment showed that the factors influencing the removal efficiencies of sulfur-containing odors were ranked from high to low as follows: temperature > weight ratio > humidity content. The combination of parameters of 20% weight ratio, 25°C temperature, and 30% water content was more recommended based on the consideration of the removal efficiencies and economic benefits. The mechanisms of sulfur conversion inside biocover were analyzed. Most organic sulfur was firstly degraded to reduced sulfides or element sulfur, and then oxidized to sulfate which could be stable in the layer as the final state. In this process, sulfur-oxidizing bacteria play a great role, and the distribution of them in reactor 1#, 5#, and 8# was specifically monitored. Bradyrhizobiaceae and Rhodospirillaceae were the dominant species which can utilize sulfide as substance to produce sulfate and element sulfur, respectively. Based on the results of OUTs, the biodiversity of these sulfur-oxidizing bacteria, these microorganisms, was demonstrated to be affected by the different parameters. These results indicate that the novel alternative landfill cover modified with bamboo charcoal compost is effective in removing sulfur odors from landfills. Meanwhile, the findings have direct implications for addressing landfill odor problems through parameter adjustment.

Quorum Sensing Regulates the Production of Methanethiol in Vibrio harveyi

Methanethiol (MeSH) and dimethyl sulfide (DMS) are important volatile organic sulfur compounds involved in atmospheric chemistry and climate regulation. However, little is known about the metabolism of these compounds in the ubiquitous marine vibrios. Here, we investigated MeSH/DMS production and whether these processes were regulated by quorum-sensing (QS) systems in Vibrio harveyi BB120. V. harveyi BB120 exhibited strong MeSH production from methionine (Met) (465 nmol mg total protein-1) and weak DMS production from dimethylsulfoniopropionate (DMSP) cleavage. The homologs of MegL responsible for MeSH production from L-Met widely existed in vibrio genomes. Using BB120 and its nine QS mutants, we found that the MeSH production was regulated by HAI-1, AI-2 and CAI-1 QS pathways, as well as the luxO gene located in the center of this QS cascade. The regulation role of HAI-1 and AI-2 QS systems in MeSH production was further confirmed by applying quorum-quenching enzyme MomL and exogenous autoinducer AI-2. By contrast, the DMS production from DMSP cleavage showed no significant difference between BB120 and its QS mutants. Such QS-regulated MeSH production may help to remove excess Met that can be harmful for vibrio growth. These results emphasize the importance of QS systems and the MeSH production process in vibrios.

Isopropylthiol emission by bloom-forming Microcystis: Biochemistry, ecophysiology and semiochemistry of a volatile organosulfur compound

Microcystis species not only produce toxic cyanobacterial blooms, but can be a significant source of taste and odour. Previous studies have associated foul-smelling volatile organic sulfur compounds (VOSCs) with Microcystis blooms, but have largely attributed these compounds to bacterial bloom decomposition. However, earlier reports of the production of isopropylthio compounds by several Microcystis strains suggests that these cyanobacteria may themselves be a source of these VOSCs. Sulphur compounds have been shown to play important semiochemical roles in algal cell protection and grazer interactions in marine systems, but little is known about the production and chemical ecology of freshwater cyanobacterial VOSCs. To address this knowledge gap, we undertook the first detailed investigation of the biochemistry, ecophysiology and semiochemistry of these compounds and their production by Microcystis, and tested the hypothesis that they act as multifunctional semiochemicals in processes related to cell protection and grazer defence. Using short-term incubations and an adapted headspace-GC-MS technique, we investigated VOSC production by axenic and non-axenic strains, and verified that isopropylthio compounds are in fact produced by these cyanobacteria, identifying 5 isopropyl moiety-containing VOSCs (isopropylthiol (ISH), isopropylmethyl sulfide, isopropyl methyl disulfide, diisopropyl disulfide (ISSI) and diisopropyl trisulfide) as well as methanethiol in three strains. Further studies with the axenic strain Microcystis PCC 7806 using different light regimes, metabolic inhibitors (sodium azide, DCMU), the antioxidant enzyme catalase and stable labelled precursors (hydrogencarbonate, acetates and sulfate) demonstrated that ISH is a true exo-metabolite, synthesized via the acetate pathway. It is actively produced and continuously excreted by the cyanobacteria during growth, with minimal internal storage or post-lysis catalytic generation. The molar ratios of the redox pair ISH/ISSI are not directly involved in the photosynthetic and respiratory electron transport chains, but dependant on the redox state of the cell - likely mediated by reactive oxygen species (ROS), as shown by a marked effect of catalase. These results, along with toxicological and behavioural assays using the two aquatic invertebrates Thamnocephalus platyurus and Daphnia magna indicate that ISH plays multiple important physiological and ecological roles. It acts as an effective antioxidant against high ROS levels, as often experienced in surface blooms, it elicits avoidance-related behavioural responses in grazer communities and at high levels, it can be toxic to some invertebrates.

Mitigation of biogenic methanethiol using bacteriophages in synthetic wastewater augmented with Pseudomonas putida

Wastewater malodour is the proverbial 'elephant in the room' notwithstanding its severe implications on sanitation, health, and hygiene. The predominant malodorous compounds associated with wastewater treatment plants and toilets are volatile organic compounds, such as hydrogen sulphide, ammonia, methanethiol, and organic acids. Among them, methanethiol warrants more attention owing to its relatively low olfactory threshold and associated cytotoxicity. This requires an efficient odour-abatement method since conventional techniques are either cost-prohibitive or leave recalcitrant byproducts. Bacteriophage-based methodology holds promise, and the described work explores the potential. In this study, a non-lysogenous Pseudomonas putida strain is used as a model organism that produces methanethiol in the presence of methionine. Two double-stranded DNA phages of genome sizes > 10 Kb were isolated from sewage. ɸPh_PP01 and ɸPh_PP02 were stable at suboptimal pH, temperature, and at 10% chloroform. Moreover, they showed adsorption efficiencies of 53% and 89% in 12 min and burst sizes of 507 ± 187 and 105 ± 7 virions per cell, respectively. In augmented synthetic wastewater, ɸPh_PP01 and ɸPh_PP02 reduced methanethiol production by 52% and 47%, respectively, with the concomitant reduction in P. putida by 3 logs in 6 h. On extension of the study in P. putida spiked-sewage sample, maximum reduction in methanethiol production was achieved in 3 h, with 49% and 48% for ɸPh_PP01 and ɸPh_PP02, respectively. But at 6 h, efficiency reduced to 36% with both the phages. The study clearly demonstrates the potential of phages as biocontrol agents in the reduction of malodour in wastewater.

Reaction mechanism and kinetics of the two-component flavoprotein dimethyl sulfone monooxygenase system: Using hydrogen peroxide for monooxygenation and substrate cleavage

The dimethyl sulfone monooxygenase system is a two-component flavoprotein, catalyzing the monooxygenation of dimethyl sulfone (DMSO2 ) by oxidative cleavage producing methanesulfinate and formaldehyde. The reductase component (DMSR) is a flavoprotein with FMN as a cofactor, catalyzing flavin reduction using NADH. The monooxygenase (DMSMO) uses reduced flavin from the reductase and oxygen for substrate monooxygenation. DMSMO can bind to FMN and FMNH- with a Kd of 17.4 ± 0.9 μm and 4.08 ± 0.8 μm, respectively. The binding of FMN to DMSMO is required prior to binding DMSO2 . This also applies to the fast binding of reduced FMN to DMSMO followed by DMSO2 . Substituting reduced DMSR with FMNH- demonstrated the same oxidation kinetics, indicating that FMNH- from DMSR was transferred to DMSMO. The oxidation of FMNH- :DMSMO, with and without DMSO2 did not generate any flavin adducts for monooxygenation. Therefore, H2 O2 is likely to be the reactive agent to attack the substrate. The H2 O2 assay results demonstrated production of H2 O2 from the oxidation of FMNH- :DMSMO, whereas H2 O2 was not detected in the presence of DMSO2 , confirming H2 O2 utilization. The rate constant for methanesulfinate formation determined from rapid quenched flow and the rate constant for flavin oxidation were similar, indicating that H2 O2 rapidly reacts with DMSO2 , with flavin oxidation as the rate-limiting step. This is the first report of the kinetic mechanisms of both components using rapid kinetics and of a method for methanesulfinate detection using LC-MS.

Methyl-Based Methanogenesis: an Ecological and Genomic Review

Methyl-based methanogenesis is one of three broad categories of archaeal anaerobic methanogenesis, including both the methyl dismutation (methylotrophic) pathway and the methyl-reducing (also known as hydrogen-dependent methylotrophic) pathway. Methyl-based methanogenesis is increasingly recognized as an important source of methane in a variety of environments. Here, we provide an overview of methyl-based methanogenesis research, including the conditions under which methyl-based methanogenesis can be a dominant source of methane emissions, experimental methods for distinguishing different pathways of methane production, molecular details of the biochemical pathways involved, and the genes and organisms involved in these processes. We also identify the current gaps in knowledge and present a genomic and metagenomic survey of methyl-based methanogenesis genes, highlighting the diversity of methyl-based methanogens at multiple taxonomic levels and the widespread distribution of known methyl-based methanogenesis genes and families across different environments.

A review on sulfur transformation during anaerobic digestion of organic solid waste: Mechanisms, influencing factors and resource recovery

Anaerobic digestion (AD) is an economical and environment-friendly technology for treating organic solid wastes (OSWs). OSWs with high sulfur can lead to the accumulation of toxic and harmful hydrogen sulfide (H₂S) during AD, so a considerable amount of studies have focused on removing H₂S emissions. However, current studies have found that sulfide induces phosphate release from the sludge containing iron‑phosphorus compounds (FePs) and the feasibility of recovering elemental sulfur (S⁰) during AD. To tap the full potential of sulfur in OSWs resource recovery, deciphering the sulfur transformation pathway and its influencing factors is required. Therefore, in this review, the sulfur species and distributions in OSWs and the pathway of sulfur transformation during AD were systematically summarized. Then, the relationship between iron (ferric compounds and zero-valent iron), phosphorus (FePs) and sulfur were analyzed. It was found that the reaction of iron with sulfide during AD drove the conversion of sulfide to S⁰ and iron sulfide compounds (FeS_x), and consequently iron was applied in sulfide abatement. In particular, ferric (hydr)oxide granules offer possibilities to improve the economic viability of hydrogen sulfide control by recovering S⁰. Sulfide is an interesting strategy to release phosphate from the sludge containing FePs for phosphorus recovery. Critical factors affecting sulfur transformation, including the carbon source, free ammonia and pretreatment methods, were summarized and discussed. Carbon source and free ammonia affected sulfur-related microbial diversity and enzyme activity and different sulfur transformation pathways in response to varying pretreatment methods. The study on S⁰ recovery, organic sulfur conversion, and phosphate release mechanism triggered by sulfur deserves further investigation. This review is expected to enrich our knowledge of the role of sulfur during AD and inspire new ideas for recovering phosphorus and sulfur resources from OSWs.

Nonredundant Dimethyl Sulfoxide Reductases Influence Salmonella enterica Serotype Typhimurium Anaerobic Growth and Virulence

Facultative anaerobic enteric pathogens can utilize a diverse array of alternate electron acceptors to support anaerobic metabolism and thrive in the hypoxic conditions within the mammalian gut. Dimethyl sulfoxide (DMSO) is produced by methionine catabolism and can act as an alternate electron acceptor to support anaerobic respiration. The DMSO reductase complex consists of three subunits, DmsA, DmsB, and DmsC, and allows bacteria to grow anaerobically with DMSO as an electron acceptor. The genomes of nontyphoidal Salmonella enterica encode three putative dmsABC operons, but the impact of the apparent genetic redundancy in DMSO reduction on the fitness of nontyphoidal S. enterica during infection remains unknown. We hypothesized that DMSO reduction would be needed for S. enterica serotype Typhimurium to colonize the mammalian gut. We demonstrate that an S. Typhimurium mutant with loss of function in all three putative DMSO reductases (ΔdmsA3) poorly colonizes the mammalian intestine when the microbiota is intact and when inflammation is absent. DMSO reduction enhances anaerobic growth through nonredundant contributions of two of the DMSO reductases. Furthermore, DMSO reduction influences virulence by increasing expression of the type 3 secretion system 2 and reducing expression of the type 3 secretion system 1. Collectively, our data demonstrate that the DMSO reductases of S. Typhimurium are functionally nonredundant and suggest DMSO is a physiologically relevant electron acceptor that supports S. enterica fitness in the gut.

Theoretical study on hydrogen transfer in the dissociation of dimethyl disulfide radical cations

Hydrogen transfer (HT) is of crucial importance in biochemistry and atmospheric chemistry. Here, HT processes involved in the dissociation reaction of dimethyl disulfide radical cations (DMDS˙⁺, CH₃SSCH₃˙⁺) are investigated using quantum chemical calculations. Four HTs from the C to S atom and one HT from the S to S atom are observed and the most probable paths are proposed in the dissociation channel from DMDS˙⁺ to CH_nS⁺ (n = 2-4). The mechanisms of all these five HTs are described as hydrogen atom transfer (HAT) and four of them are accompanied by electron transfer (ET). Considering the catalytic effect of water molecules existing in organisms and the atmosphere, five HT processes in the dissociation of the [DMDS + H₂O]˙⁺ complex are further explored, which show lower free energy barriers. With the participation of water molecules acting as a base, two HTs from the C to the S atom, which have the largest decrease in energy barriers, are characterized as concerted proton-coupled electron transfer (cPCET). These results can be extended to understand the mechanism of the HT process during the dissociation of disulfide and help provide a strategy to design a rare cPCET mechanism for the activation of the C-H bond.

Estimation of sulfur fate and contribution to VSC emissions from lakes during algae decay

Algae decay is an important process influencing environmental variables and emissions of volatile sulfur compounds (VSCs) in eutrophic lakes. However, effects of algae decay on VSC emissions from eutrophic lakes as well as fate of algae-derived sulfur remain poorly understood. In this study, simulated algae-sediment systems were used to explore the flow and distribution of sulfur during algae decay. VSCs including hydrogen sulfide (H₂S), methanethiol (CH₃SH), carbon disulfide (CS₂) and dimethyl sulfide ((CH₃)₂S) were detected during algae decay, which increased with algae biomass and eutrophic levels in lakes. During algae decay, the highest H₂S, CH₃SH and (CH₃)₂S emission rates of 10.45, 21.82 and 43.26 μg d^-1 occurred in the first 1-2 days, respectively, while the highest CS₂ emission rates were observed between days 8 and 11. The maximum emissions of H₂S and CS₂ from algae decay were estimated at 0.51 and 0.35 mg m^-2 d^-1 in Lake Taihu, accounting for 1.57% and 0.69% of the total H₂S and CS₂ emissions of in situ, respectively. Algae decay could significantly increase the contents of total sulfur and total carbon in sediments by 2.90%-21.11% and 4.23%-45.05%, respectively. The VSC emissions during algae decay could be predicted using the multiple regression models with the contents of total carbon, total nitrogen and sulfur-containing compounds in sediments. Partial least squares path modelling demonstrated that algae decay had a low direct effect on VSC emissions with a strength of 0.06, while it had a significant influence on environmental variables with a strength of 0.63, which could affect VSC emissions with a strength of 0.85, indicating VSC emissions from eutrophic lakes were affected by the environmental variables rather than the direct influence of algae decay. These findings illustrated the mechanisms of VSC emissions during algae decay and provided insights into VSC control and mitigation for eutrophic lakes.

Volatile organic compound emissions in free-range chicken production: Impacts on environment, welfare and sustainability

<abstract> <p>The increasing demand for free-range poultry products has led to a surge in their availability in the market, prompting a potential decline in premium prices associated with these products. This shift places considerable pressure on upstream costs in chicken production. A comprehensive under-standing of its impact on the environment is essential to ensure the success of commercial and industrial free-range chicken production. However, there exists a significant knowledge gap concerning the emission and concentrations of volatile organic compounds (VOCs) from organic-free range chicken, and their environmental implications have yet to be understood. We aim to address this critical knowledge gap by elucidating the role of VOC emissions in chicken production and assessing their impact on human and animal health, as well as environmental challenges. Understanding the implications of VOC emissions is essential for promoting sustainable and responsible free-range chicken farming practices. By identifying the sources of VOC emissions and their impacts, stakeholders can implement appropriate measures to optimize air quality and enhance the well-being of chickens and workers. Ultimately, this review highlights the role of VOCs in animal production, providing valuable insights for improving the efficiency, environmental sustainability and welfare aspects of free-range chicken farming.</p> </abstract>

Discovery of Homogentisic Acid as a Precursor in Trimethoprim Metabolism and Natural Product Biosynthesis

Opportunistic infections by Burkholderia cenocepacia are life threatening for patients suffering from cystic fibrosis and chronic granulomatous disease. These infections are often associated with variable clinical outcomes, prompting an interest in molecular investigations of phenotypes associated with disease severity. The production of the pyomelanin pigment is one such phenotype, which was recently linked to the ability of clinical strains to carry out biotransformation of the antibiotic trimethoprim. However, this biotransformation product was not identified, and differences in metabolite production associated with pyomelanin pigmentation are poorly understood. Here, we identify several key metabolites produced exclusively by the pyomelanin-producing strains. To provide insight into the structures and biosynthetic origin of these metabolites, we developed a mass spectrometry-based strategy coupling unsupervised in silico substructure prediction with stable isotope labeling referred to as MAS-SILAC (Metabolite Annotation assisted by Substructure discovery and Stable Isotope Labeling by Amino acids in Cell culture). This approach led to discovery of homogentisic acid as a precursor for biosynthesis of several natural products and for biotransformation of trimethoprim, representing a previously unknown mechanism of antibiotic tolerance. This work presents application of computational methods for analysis of untargeted metabolomic data to link the chemotype of pathogenic microorganisms with a specific phenotype. The observations made in this study provide insights into the clinical significance of the melanated phenotype.

Changes of wort characteristic components through low thermal stress boiling

This paper systematically studied the changes of wort characteristic components under various low thermal stress boiling, and separation methods of Dimethyl-Sulfide (DMS) accumulated in wort due to low thermal stress boiling. Compared with conventional boiling, the combined boiling (boiling at 3% evaporation rate and 98 °C holding temperature for 30 min) demonstrated that the change rates of solidifiable nitrogen, iso-α-acid and color were no more than 5%, the absorbance of thiobarbituric acid (TBA) reaction mixture decreased by 13.7%, and DMS can be separated by vacuum film stripping after whirlpool. For 98 °C holding temperature boiling, the differences in absorbance of TBA reaction mixture, iso-α-acid and color were 16, 11.6 and 5%, respectively. The solidifiable nitrogen content was equivalent to the 28 mg/L limit and DMS must be removed by vacuum film stripping two times. From the perspective of application, it is necessary to improve the separation efficiency of DMS subsequently.

Separation of Dimethyl Sulfide from Wort by Multi-Layer Centrifugal Film Method

Installing a separation device for undesirable volatile substances represented by dimethyl sulfide (DMS) in wort boiling systems is a common way to reduce the thermal stress and maintain the beer’s flavor stability (characterized by the thiobarbituric acid (TBA) value), but most of these separation devices need to provide additional vacuum or primary thermal energy. This research shows that it can produce self-evaporation that consumes its own sensible heat when wort is in the state of turbulent film. Therefore, a new gas-liquid separation system named the multilayer centrifugal film-forming device (similar to the spinning cone column (SCC)) is proposed, which can strengthen self-evaporation through wort turbulent film and create gas phase conditions for the separation of undesirable volatile substances. The results show that up to 91.6% of the content of DMS in wort could be significantly removed by centrifugal film self-evaporation. The TBA value of wort was reduced by more than 15%, and the wort was not found to be oxidized. Compared with the traditional boiling method, the multi-layer centrifugal film-forming device can significantly save primary energy consumption and reduce energy consumption by 216.4 kJ per liter of wort during the boiling and cooling process.

Comparative evaluation of encapsulation using β-cyclodextrin versus freeze-drying for better retention and stabilizing of black Périgord truffle (Tuber melanosporum) aroma

This study aimed to develop a novel technique to retain and stabilize compounds contributing to truffle aroma by encapsulation using β-cyclodextrin. Two experiments were conducted. In the first experiment, the key volatile profile and microbial population of products resulting from three different encapsulation methods, namely direct mixing method (M1), direct mixing followed by ethanol addition method (M2), and paste method (M3), were compared with untreated truffles (positive control) over a 90-day period. The M2-derived product was the least optimal for retaining key volatile compounds despite showing the lowest microbial population. There was no significant difference in the volatile profile of products derived from M1 and M3 on day 0. However, it was observed that the M3-derived product could retain its volatile profile better than the M1-derived product by day 90. M3 was compared with freeze-drying in the second experiment. Freeze-dried truffles showed an overall higher relative percentage of volatiles than the M3-derived product on day 0. However, by day 90, some volatile changes occurred in the freeze-dried truffles but not in the M3-derived product. The findings indicate that while freeze-drying could adequately conserve truffle volatiles, the encapsulation of volatile compounds in β-cyclodextrin could improve the volatile stability of truffle products and allow for longer storage times. Microbes were found in all encapsulated truffle products and freeze-dried truffles on days 0 and 90, suggesting the need to explore the possibility of incorporating a decontamination step in the process prior to either encapsulation or freeze-drying. PRACTICAL APPLICATION: A technique to capture and stabilize compounds responsible for truffle aroma by encapsulation using β-cyclodextrin was developed and compared with freeze-drying in this study. The overall finding suggests that while freeze-drying of truffle could sufficiently preserve volatiles, encapsulating truffle volatiles with β-cyclodextrin may improve its stability, extending its shelf life, which can be applied in the development of a natural truffle ingredient that can be applied in food product development.

Microbial compositions, ecological networks, and metabolomics in sediments of black-odour water in Dongguan, China

Black-odour water with organic compounds and heavy metals caused by domestic and industrial activities has aroused people's attention in recent years, yet little is known about the ecological effects on aquatic organisms, especially microorganisms in sediments. To explore the response of microbial communities to environmental factors, the community and metabolites of nine river sediments with different pollution in Dongguan city, China were investigated using 16S rRNA gene sequencing and liquid chromatography tandem-mass. The results revealed that the composition and structure of sedimentary microbial communities significantly changed in rivers with varying pollution levels. Cyanobacteria were the most abundant organisms in the sediment of black-odorous rivers, while the relative abundance of Thaumarchaeota was gradually increased with the river quality gets better. The relative abundance of organic acids (including amino acids), alcohols, esters, and ketones associated with microbial metabolism in sediments of polluted rivers was increased. The 16S rRNA gene sequencing-based molecular ecological network analysis indicated that the interactions amongst bacteria were enhanced in severely contaminated communities. Sphingomonadaceae and Cyanobacteria have important roles in bacterial community structures of polluted rivers and those with ongoing treatment. The correlation analysis showed significant metal resistance and/or tolerance of the following bacteria species Thalassiosira weissflogii, Aminicenantes bacterium clone OPB95, 'Candidatus Halomonas phosphatis', and archaeal species Methanolinea and unidentified Thermoplasmata. These results indicated that sedimentary microbial communities may shift in composition and structure, as well as their interaction network, to adapt and resist environmental contamination and promote restoration.

CS2 increasing CH4-derived carbon emissions and active microbial diversity in lake sediments

Lakes are important methane (CH₄) sources to the atmosphere, especially eutrophic lakes with cyanobacterial blooms accompanied by volatile sulfur compound (VSC) emissions. CH₄ oxidation is a key strategy to mitigate CH₄ emission from lakes. In this study, we characterized the fate of CH₄-derived carbon and active microbial communities in lake sediments with CS₂ used as a typical VSC, based on the investigation of CH₄ and VSC fluxes from Meiliang Bay in Lake Taihu. Stable isotope probing microcosm incubation showed that the efficiency of CH₄-derived carbon incorporated into organic matter was 21.1% in the sediment with CS₂ existence, which was lower than that without CS₂ (27.3%). SO₄^2--S was the main product of CS₂ oxidation under aerobic condition, accounting for 59.3-62.7% of the input CS₂-S. CS₂ and CH₄ coexistence led to a decrease of methanotroph and methylotroph abundances and stimulated the production of extracellular polymeric substances. CS₂ and its metabolites including total sulfur, SO₄^2- and acid volatile sulfur acted as the main drivers influencing the active microbial community structure in the sediments. Compared with α-proteobacteria methanotrophs, γ-proteobacteria methanotrophs Methylomicrobium, Methylomonas, Crenothrix and Methylosarcina were more dominant in the sediments. CH₄-derived carbon mainly flowed into methylotrophs in the first stage. With CH₄ consumption, more CH₄-derived carbon flowed into non-methylotrophs. CS₂ could prompt more CH₄-derived carbon flowing into non-methanotrophs and non-methylotrophs, such as sulfur-metabolizing bacteria. These findings can help elucidate the influence of VSCs on microorganisms and provide insights to carbon fluxes from eutrophic lake systems.

SEMO-1, a novel methanethiol oxidase in Caenorhabditis elegans, is a pro-aging factor conferring selective stress resistance

Methanethiol is a toxic gas produced through bacterial degradation of sulfur-containing amino acids. Applying a novel enzymatic assay, we here identified a methanethiol oxidase (MTO) that catalyzes the degradation of methanethiol in the nematode Caenorhabditis elegans (C. elegans). The corresponding protein, Y37A1B.5, previously characterized as a C. elegans ortholog of human selenium-binding protein 1 (SELENBP1), was renamed SEMO-1 (SELENBP1 ortholog with methanethiol oxidase activity). Worms rendered deficient in SEMO-1 not only showed decreased hydrogen sulfide production from methanethiol catabolism but they were also more resistant to oxidative stress and had an elevated life span. In contrast, resistance to selenite was significantly lowered in SEMO-1-deficient worms. Naturally occurring mutations of human SELENBP1 were introduced to recombinant SEMO-1 through site-directed mutagenesis and resulted in loss of its MTO activity, indicating a similar enzymatic mechanism for SELENBP1 and SEMO-1. In summary, SEMO-1 confers resistance to toxic selenite and the ability to metabolize toxic methanethiol. These beneficial effects might be a trade-off for its negative impact on C. elegans life span.

New Insights into the Origin of Volatile Sulfur Compounds during Wine Fermentation and Their Evolution during Aging

Volatile sulfur compounds (VSCs) are associated with unpleasant reductive aromas and are responsible for an important reduction in wine quality, causing major economic losses. Understanding the origin of these compounds in wine remains a challenge, as their formation and further evolution during winemaking can involve both chemical and biological reactions. Comparing the VSCs profile (i) of fermenting synthetic grape juices supplemented with a selected VSC (eight compounds tested) and incubated in presence or absence of yeast, and (ii) during storage of wines under an accelerated aging procedure, allowed us to elucidate the chemical and metabolic connections between VSCs during fermentation and aging. Yeast metabolism, through the Ehrlich pathway and acetylation reactions, makes an important contribution to the formation of compounds such as methionol, 3-methylthiopropionate, 3-methylthiopropylacetate, 3-mercaptopropanol, 2-mercaptoethanol and thioesters. By contrast, chemical reactions are responsible for interconversions between thiols and disulfides, the formation of thiols from thioesters or, more surprisingly, the formation of ethylthiopropanol from methionol during fermentation. During aging, variations in heavy VSC concentrations, such as an increase in 3-methylthiopropylacetate and a decrease in ethyl-3-methylthiopropionate formation, were evidenced. Overall, this study highlights that it is essential to consider both yeast metabolism and the high chemical reactivity of VSCs to understand their formation and evolution during winemaking.

Methods used for extraction of plant volatiles have potential to preserve truffle aroma: A review

Truffles are considered one of the world's most highly prized foods mainly due to their desirable organoleptic properties and rarity. However, truffles are seasonal (harvested mostly in winter from June to August in the Southern Hemisphere and from December to February in the Northern Hemisphere) and extremely perishable. Truffles deteriorate rapidly showing undesirable changes within 10 days from harvest in aroma and visual appearance after harvest. The very short postharvest shelf life (about 7-10 days) limits the potential for export and domestic consumption all year round. Several preservation methods have been studied to prolong their shelf life without the loss of aroma. However, all traditional preservation techniques have their own shortcomings and remain challenging. The extraction of natural truffle aroma volatiles for food applications could be a potential alternative to replace the existing synthetic flavoring used for processed truffle products. Four commonly used extraction methods for recovering volatile compounds from plants, namely, supercritical carbon dioxide extraction, Soxhlet extraction, distillation, and cold pressing, are critically analyzed. Up to date, existing research about the extraction of aroma volatiles from truffles is limited in the literature but based on the volatility of the key truffle volatile compounds, supercritical carbon dioxide extraction may offer the best possibility so that a natural truffle-based product that can be used in food applications throughout the year can be made available.

Co-Treatment with Single and Ternary Mixture Gas of Dimethyl Sulfide, Propanethiol, and Toluene by a Macrokinetic Analysis in a Biotrickling Filter Seeded with Alcaligenes sp. SY1 and Pseudomonas Putida S1

The biotrickling filter (BTF) treatment is an effective way of dealing with air pollution caused by volatile organic compounds (VOCs). However, this approach is typically used for single VOCs treatment but not for the mixtures of VOC and volatile organic sulfur compounds (VOSCs), even if they are often encountered in industrial applications. Therefore, we investigated the performance of BTF for single and ternary mixture gas of dimethyl sulfide (DMS), propanethiol, and toluene, respectively. Results showed that the co-treatment enhanced the removal efficiency of toluene, but not of dimethyl sulfide or propanethiol. Maximum removal rates (rmax) of DMS, propanethiol and toluene were calculated to be 256.41 g·m−3·h−1, 204.08 g·m−3·h−1 and 90.91 g·m−3·h−1, respectively. For a gas mixture of these three constituents, rmax was measured to be 114.94 g·m−3·h−1, 104.17 g·m−3·h−1 and 99.01 g·m−3·h−1, separately. Illumina MiSeq sequencing analysis further indicated that Proteobacteria and Bacteroidetes were the major bacterial groups in BTF packing materials. A shift of bacterial community structure was observed during the biodegradation process.

Biochemical Mapping of Pyrodinium bahamense Unveils Molecular Underpinnings behind Organismal Processes

Proteins, lipids, and carbohydrates from the harmful algal bloom (HAB)-causing organism Pyrodinium bahamense were characterized to obtain insights into the biochemical processes in this environmentally relevant dinoflagellate. Shotgun proteomics using label-free quantitation followed by proteome mapping using the P. bahamense transcriptome and translated protein databases of Marinovum algicola, Alexandrium sp., Cylindrospermopsis raciborskii, and Symbiodinium kawagutii for annotation enabled the characterization of the proteins in P. bahamense. The highest number of annotated hits were obtained from M. algicola and highlighted the contribution of microorganisms associated with P. bahamense. Proteins involved in dimethylsulfoniopropionate (DMSP) degradation such as propionyl CoA synthethase and acryloyl-CoA reductase were identified, suggesting the DMSP cleavage pathway as the preferred route in this dinoflagellate. Most of the annotated proteins were involved in amino acid biosynthesis and carbohydrate degradation and metabolism, indicating the active roles of these molecules in the vegetative stage of P. bahamense. This characterization provides baseline information on the cellular machinery and the molecular basis of the ecophysiology of P. bahamense.

Expanding Characterized Diversity and the Pool of Complete Genome Sequences of Methylococcus Species, the Bacteria of High Environmental and Biotechnological Relevance

The bacterial genus Methylococcus, which comprises aerobic thermotolerant methanotrophic cocci, was described half-a-century ago. Over the years, a member of this genus, Methylococcus capsulatus Bath, has become a major model organism to study genomic and metabolic basis of obligate methanotrophy. High biotechnological potential of fast-growing Methylococcus species, mainly as a promising source of feed protein, has also been recognized. Despite this big research attention, the currently cultured Methylococcus diversity is represented by members of the two species, M. capsulatus and M. geothermalis, while finished genome sequences are available only for two strains of these methanotrophs. This study extends the pool of phenotypically characterized Methylococcus strains with good-quality genome sequences by contributing four novel isolates of these bacteria from activated sludge, landfill cover soil, and freshwater sediments. The determined genome sizes of novel isolates varied between 3.2 and 4.0Mb. As revealed by the phylogenomic analysis, strains IO1, BH, and KN2 affiliate with M. capsulatus, while strain Mc7 may potentially represent a novel species. Highest temperature optima (45-50°C) and highest growth rates in bioreactor cultures (up to 0.3h-1) were recorded for strains obtained from activated sludge. The comparative analysis of all complete genomes of Methylococcus species revealed 4,485 gene clusters. Of these, pan-genome core comprised 2,331 genes (on average 51.9% of each genome), with the accessory genome containing 846 and 1,308 genes in the shell and the cloud, respectively. Independently of the isolation source, all strains of M. capsulatus displayed surprisingly high genome synteny and a striking similarity in gene content. Strain Mc7 from a landfill cover soil differed from other isolates by the high content of mobile genetic elements in the genome and a number of genome-encoded features missing in M. capsulatus, such as sucrose biosynthesis and the ability to scavenge phosphorus and sulfur from the environment.

Structures of the alkanesulfonate monooxygenase MsuD provide insight into C-S bond cleavage, substrate scope, and an unexpected role for the tetramer

Bacterial two-component flavin-dependent monooxygenases cleave the stable C-S bond of environmental and anthropogenic organosulfur compounds. The monooxygenase MsuD converts methanesulfonate (MS-) to sulfite, completing the sulfur assimilation process during sulfate starvation, but the mechanism of this conversion remains unclear. To explore the mechanism of C-S bond cleavage, we report a series of crystal structures of MsuD from Pseudomonas fluorescens in different liganded states. This report provides the first crystal structures of an alkanesulfonate monooxygenase with a bound flavin and alkanesulfonate, elucidating the roles of the active site lid, the protein C terminus, and an active site loop in flavin and/or alkanesulfonate binding. These structures position MS- closest to the flavin N5 position, consistent with an N5-(hydro)peroxyflavin mechanism rather than a classical C4a-(hydro)peroxyflavin mechanism. A fully enclosed active site is observed in the ternary complex, mediated by interchain interaction of the C terminus at the tetramer interface. These structures identify an unexpected function of the protein C terminus in this protein family in stabilizing tetramer formation and the alkanesulfonate-binding site. Spurred by interest from the crystal structures, we conducted biochemical assays and molecular docking that redefine MsuD as a small- to medium-chain alkanesulfonate monooxygenase. Functional mutations verify the sulfonate-binding site and reveal the critical importance of the protein C terminus for monooxygenase function. These findings reveal a deeper understanding of MsuD's functionality at the molecular level and consequently how it operates within its role as part of the sulfur assimilation pathway.

Microbial volatile organic compounds in intra-kingdom and inter-kingdom interactions

Microorganisms produce and excrete a versatile array of metabolites with different physico-chemical properties and biological activities. However, the ability of microorganisms to release volatile compounds has only attracted research attention in the past decade. Recent research has revealed that microbial volatiles are chemically very diverse and have important roles in distant interactions and communication. Microbial volatiles can diffuse fast in both gas and water phases, and thus can mediate swift chemical interactions. As well as constitutively emitted volatiles, microorganisms can emit induced volatiles that are triggered by biological interactions or environmental cues. In this Review, we highlight recent discoveries concerning microbial volatile compounds and their roles in intra-kingdom microbial interactions and inter-kingdom interactions with plants and insects. Furthermore, we indicate the potential biotechnological applications of microbial volatiles and discuss challenges and perspectives in this emerging research field.

Effect of substrate sulfur state on MM and DMS emissions in landfill

Methyl mercaptan (MM) and dimethyl sulfide (DMS) are typical landfill odorous gases that have received little attention compared with hydrogen sulfide (H₂S). In this study, landfill MM and DMS emissions were investigated regarding their origin from substrates with different sulfur states, namely, intrinsic organic sulfur and external inorganic sulfur (SO₄^2-). Substrates with high protein contents showed the highest potential for MM and DMS emissions, at 46.0 and 9.2 μL·g^-1 substrate, respectively. Meanwhile, a comparable contribution by SO₄^2- was achieved when the SO₄^2- content comprised over 40% of the substrate. The substrate contribution to DMS emission was up to 10 times the SO₄^2- contribution. Meanwhile, the SO₄^2- contribution to MM emission was over 1000 times that to DMS emissions. MM and DMS can accumulate in landfill sites and then be transformed into H₂S or sulfide (S^2-). This research offers a comprehensive understanding of MM and DMS emissions in landfill and provides a basis for classification management methods in landfill sites.

Computational Study Investigating the Atmospheric Oxidation Mechanism and Kinetics of Dipropyl Thiosulfinate Initiated by OH Radicals and the Fate of Propanethiyl Radical

The OH radical-initiated atmospheric oxidation mechanism of dipropyl thiosulfinate (CH₃CH₂CH₂-S(O)S-CH₂CH₂CH₃, DPTS), a volatile released by Allium genus plants, has been investigated using ab initio/DFT electronic structure calculations. The DPTS + ^•OH reaction can proceed through (1) abstraction and (2) substitution pathways. The present calculations show that addition of ^•OH to the sulfur atom of the sulfinyl (-S(═O)) group, followed by simultaneous cleavage of the S-S single bond, leading to the formation of propanethiyl radical (PTR) and propanesulfinic acid, is the major pathway when compared to the other possible abstraction and substitution reactions. The barrier height for this reaction was computed to be -5.4 kcal mol^-1 relative to that of the separated DPTS + ^•OH reactants. The rate coefficients for all the possible pathways for DPTS + ^•OH were explored by RRKM-ME calculations using the MESMER kinetic code in the atmospherically relevant temperatures T = 200-300 K and the pressure range of 0.1-10 atm. The calculated total rate coefficient for the DPTS + ^•OH reaction was found to be 1.7 × 10^-10 cm³ molecule^-1 s^-1 at T = 300 K and P = 1 atm. The branching ratios and atmospheric lifetime of DPTS + ^•OH were also determined in the studied temperature range. In addition, electronic structure calculations on the multichannel reactions of PTR with atmospheric oxygen (³O₂) were investigated using the same level of theory. The calculations showed that unimolecular elimination of hydroperoxyl radical (HO₂) from the RO₂ adduct through formation of propanethial is a major reaction under atmospherically relevant conditions. The overall results suggest that the atmospheric removal of DPTS is mainly due to reactions with ^•OH and ³O₂, resulting in formation of propanesulfinic acid, propanethial, HO₂, and sulfur dioxide (SO₂) as the major products. The atmospheric lifetime of DPTS was estimated to be less than 2 h in the studied temperature range. Estimations of the global warming potential of DPTS and the products of its reaction with ^•OH reveal that while the contribution made by DPTS to global warming is negligible, the various products formed as a consequence of its interaction with OH radical may make substantial contributions to global warming, acid rain, and formation of secondary organic aerosols.

Sulfate reduction behavior in the leachate saturated zone of landfill sites

Municipal solid waste landfills are considered one of the most important parts of the sulfur cycle. However, few studies have focused on sulfate reduction in the leachate saturated zone, where the temperature may be variable. In this work, the sulfate reduction behavior was evaluated in a landfill leachate saturated zone under temperatures between 30 and 80 °C. The results show that microbial sulfate reduction is high in the saturated zone, especially when the temperature is at 50-60 °C. The microbial diversity and the abundance of functional genes results reveal that specific sulfate-reducing bacteria such as Dethiobacter, the bacteria that offer energy to them, and genes other than dsrA and dsrB may have a close relationship with the variation in the reduction of sulfate. This work may improve the knowledge of sulfate reduction in the landfill sites and therefore offer theoretical support to management strategies.

Cell death associated release of volatile organic sulphur compounds with antioxidant properties in chemical-challenged tobacco BY-2 suspension cultured cells

The production of volatile organic compounds (VOCs) during programmed cell death (PCD) is still insufficiently studied and their implication in the process is not well understood. The present study demonstrates that the release of VOSCs with presumed antioxidant capacity (methanethiol, dimethylsulfide and dimethyldisulfide) accompanies the cell death in chemical-stressed tobacco BY-2 suspension cultured cells. The cells were exposed to cell death inducers of biotic nature mastoparan (MP, wasp venom) and camptothecin (CPT, alkaloid), and to the abiotic stress agent CdSO4. The VOCs emission was monitored by proton-transfer reaction mass spectrometry (PTR-MS). The three chemicals induced PCD expressing apoptotic-like phenotype. The identified VOSCs were emitted in response to MP and CPT but not in presence of Cd. The VOSCs production occurred within few hours after the administration of the elicitors, peaked up when 20-50 % of the cells were dead and further levelled off with cell death advancement. This suggests that VOSCs with antioxidant activity may contribute to alleviation of cell death-associated oxidative stress at medium severity of cell death in response to the stress factors of biotic origin. The findings provide novel information about cell death defence mechanisms in chemical-challenged BY-2 cells and show that PCD related VOSCs synthesis depends on the type of inducer.

Organosulfates in Ambient Aerosol: State of Knowledge and Future Research Directions on Formation, Abundance, Fate, and Importance

Organosulfates (OSs), also referred to as organic sulfate esters, are well-known and ubiquitous constituents of atmospheric aerosol particles. Commonly, they are assumed to form upon mixing of air masses of biogenic and anthropogenic origin, that is, through multiphase reactions between organic compounds and acidic sulfate particles. However, in contrast to this simplified picture, recent studies suggest that OSs may also originate from purely anthropogenic precursors or even directly from biomass and fossil fuel burning. Moreover, besides classical OS formation pathways, several alternative routes have been discovered, suggesting that OS formation possibly occurs through a wider variety of formation mechanisms in the atmosphere than initially expected. During the past decade, OSs have reached a constantly growing attention within the atmospheric science community with evermore studies reporting on large numbers of OS species in ambient aerosol. Nonetheless, estimates on OS concentrations and implications on atmospheric physicochemical processes are still connected to large uncertainties, calling for combined field, laboratory, and modeling studies. In this Critical Review, we summarize the current state of knowledge in atmospheric OS research, discuss unresolved questions, and outline future research needs, also in view of reductions of anthropogenic sulfur dioxide (SO₂) emissions. Particularly, we focus on (1) field measurements of OSs and measurement techniques, (2) formation pathways of OSs and their atmospheric relevance, (3) transformation, reactivity, and fate of OSs in atmospheric particles, and (4) modeling efforts of OS formation and their global abundance.

Simultaneous methanethiol and dimethyl sulfide removal in a single-stage biotrickling filter packed with polyurethane foam: Performance, parameters and microbial community analysis

The bio-treatment of methanethiol (MT) and dimethyl sulfide (DMS), the most common sulfur compounds in odorous gas, is difficult due to the inhibition of DMS degradation by MT. This article investigated the treatment of MT and DMS odorous gas using a single-stage biotrickling filter (BTF) packed with polyurethane foam cubes that were inoculated with activated sludge from a sewage treatment plant operating an anaerobic/aerobic/oxic (AAO) process. The BTF system lasted for 161 days (with 9 days to startup) under an empty gas residence time of 39 s. The elimination capacities for MT and DMS were 85.2 g/m³/h (removal efficiency = 96.6%) and 6.4 g/m³/h (removal efficiency = 95.0%), respectively, and the maximal elimination capacities of MT and DMS were 119.7 g/m³/h and 7.3 g/m³/h, respectively. The optimal parameters were as follows: empty bed retention time, 39 s; pH, 6.1; recirculation medium flow rate, ≥1.2 m³/m²/h; temperature, 29-36 °C; and SO₄^2- concentration, < 2.0 g-SO₄^2-/L. Microbial community analysis revealed that spatial differentiation between MT-degrading bacteria and DMS-degrading bacteria enable the single-stage BTF can simultaneously remove MT and DMS. The activated sludge of AAO process can be used as the inoculation sludge to treating MT and DMS gas, which provides an important reference for the industrial application of treating odorous gas containing MT and DMS.

Structure and function of the two-component flavin-dependent methanesulfinate monooxygenase within bacterial sulfur assimilation

Methyl sulfur compounds are a rich source of environmental sulfur for microorganisms, but their use requires redox systems. The bacterial sfn and msu operons contain two-component flavin-dependent monooxygenases for dimethylsulfone (DMSO₂) assimilation: SfnG converts DMSO₂ to methanesulfinate (MSI^-), and MsuD converts methanesulfonate (MS^-) to sulfite. However, the enzymatic oxidation of MSI^- to MS^- has not been demonstrated, and the function of the last enzyme of the msu operon (MsuC) is unresolved. We employed crystallographic and biochemical studies to identify the function of MsuC from Pseudomonas fluorescens. The crystal structure of MsuC adopts the acyl-CoA dehydrogenase fold with putative binding sites for flavin and MSI^-, and functional assays of MsuC in the presence of its oxidoreductase MsuE, FMN, and NADH confirm the enzymatic generation of MS^-. These studies reveal that MsuC converts MSI^- to MS^- in sulfite biosynthesis from DMSO₂.

Microbial reduction of organosulfur compounds at cathodes in bioelectrochemical systems

Organosulfur compounds, present in e.g. the pulp and paper industry, biogas and natural gas, need to be removed as they potentially affect human health and harm the environment. The treatment of organosulfur compounds is a challenge, as an economically feasible technology is lacking. In this study, we demonstrate that organosulfur compounds can be degraded to sulfide in bioelectrochemical systems (BESs). Methanethiol, ethanethiol, propanethiol and dimethyl disulfide were supplied separately to the biocathodes of BESs, which were controlled at a constant current density of 2 A/m² and 4 A/m². The decrease of methanethiol in the gas phase was correlated to the increase of dissolved sulfide in the liquid phase. A sulfur recovery, as sulfide, of 64% was found over 5 days with an addition of 0.1 ​mM methanethiol. Sulfur recoveries over 22 days with a total organosulfur compound addition of 1.85 ​mM were 18% for methanethiol and ethanethiol, 17% for propanethiol and 22% for dimethyl disulfide. No sulfide was formed in electrochemical nor biological control experiments, demonstrating that both current and microorganisms are required for the conversion of organosulfur compounds. This new application of BES for degradation of organosulfur components may unlock alternative strategies for the abatement of anthropogenic organosulfur emissions.

Contrary to Marine Environments, Common Microplastics in Freshwater Systems May Not Emit Dimethyl Sulfide: An Important Infochemical

The ingestion of microplastics by marine species has been at least partially attributed to plastics emitting a dimethyl sulfide signature when exposed to marine conditions. Dimethyl sulfide, a member of the volatile organic sulfur compounds group, is an infochemical that many species rely on to locate and identify prey while foraging. Microplastic ingestion is also observed in freshwater systems; however, this study shows that the same dimethyl sulfide signature is not obtained by three common types of plastic (high-density polyethylene, low-density polyethylene, and polystyrene) in freshwater systems, suggesting that there may be an alternate mechanism driving plastic ingestion by freshwater species.

Coral endosymbionts (Symbiodiniaceae) emit species-specific volatilomes that shift when exposed to thermal stress

Biogenic volatile organic compounds (BVOCs) influence organism fitness by promoting stress resistance and regulating trophic interactions. Studies examining BVOC emissions have predominantly focussed on terrestrial ecosystems and atmospheric chemistry - surprisingly, highly productive marine ecosystems remain largely overlooked. Here we examined the volatilome (total BVOCs) of the microalgal endosymbionts of reef invertebrates, Symbiodiniaceae. We used GC-MS to characterise five species (Symbiodinium linucheae, Breviolum psygmophilum, Durusdinium trenchii, Effrenium voratum, Fugacium kawagutii) under steady-state growth. A diverse range of 32 BVOCs were detected (from 12 in D. trenchii to 27 in S. linucheae) with halogenated hydrocarbons, alkanes and esters the most common chemical functional groups. A thermal stress experiment on thermally-sensitive Cladocopium goreaui and thermally-tolerant D. trenchii significantly affected the volatilomes of both species. More BVOCs were detected in D. trenchii following thermal stress (32 °C), while fewer BVOCs were recorded in stressed C. goreaui. The onset of stress caused dramatic increases of dimethyl-disulfide (98.52%) in C. goreaui and nonanoic acid (99.85%) in D. trenchii. This first volatilome analysis of Symbiodiniaceae reveals that both species-specificity and environmental factors govern the composition of BVOC emissions among the Symbiodiniaceae, which potentially have, as yet unexplored, physiological and ecological importance in shaping coral reef community functioning.

Taste and odor compounds associated with aquatic plants in Taihu Lake: distribution and producing potential

The odor problem caused by the decay of aquatic plants is widespread in many freshwater lakes. In this study, the spatial distributions of seven taste and odor (T&O) compounds (dimethyl sulfide, dimethyl disulfide, dimethyl trisulfide, 2-methylisoborneol, geosmin, β-cyclocitral, and β-ionone) in the sediments and overlying water of the east of Taihu Lake were investigated. The effects of plant and physico-chemical parameters on the release of T&O compounds were also analyzed. The results showed that high concentrations of T&O compounds were detected in the area where Eichhornia crassipes was flourishing. Volatile organic sulfur compounds were not found in the water source area, which was not covered by aquatic plants. High plant biomass and aquiculture activities might increase the release of the taste and odor compounds. The correlation between the concentrations of odorous compounds and nutrients in the sediment was also analyzed. The production of odorants was positively correlated with the nitrogen, and they may migrate from sediment to overlying water. The result suggested that controlling the plant density and aquaculture activities could reduce the release of odorous compounds.

Shift of Sediments Bacterial Community in the Black-Odor Urban River during In Situ Remediation by Comprehensive Measures

The phenomenon of black-odor urban rivers with rapid urbanization has attracted extensive attention. In this study, we investigated the water quality and composition of sediment-associated bacteria communities in three remediation stages (before remediation, 30 days after remediation, and 90 days after remediation) based on the in situ remediation using comprehensive measures (physical, chemical, and biological measures). The results show that the overlying water quality was notably improved after in situ remediation, while the diversity and richness of sediment-associated bacterial communities decreased. A growing trend of some dominant genus was observed following the remediation of a black-odor river, such as Halomonas, Pseudomonas, Decarbonamis, Leptolina, Longilina, Caldiseericum, Smithella, Mesotoga, Truepera, and Ralstonia, which play an important role in the removal of nitrogen, organic pollutants and hydrogen sulfide (H2S) during the sediment remediation. Redundancy analysis (RDA) showed that the bacterial community succession may accelerate the transformation of organic pollutants into inorganic salts in the sediment after in situ remediation. In a word, the water quality of the black-odor river was obviously improved after in situ remediation, and the bacterial community in the sediment notably changed, which determines the nutrients environment in the sediment.