Degradation of Dimethyl Disulfide byPseudomonas fluorescensStrain 76

Super enhancement of methanethiol biodegradation by new isolated Pseudomonas sp. coupling silicone particles

A new strain, Pseudomonas sp. SJ-1, which was able to remove model odorous organics methanethiol (MT) has been isolated from the wastewater treatment plant and identified via 16S rRNA analysis. Initial MT concentration, temperature and pH played an important role in MT removal, and up to 100% of 260 mg L^-1 of MT could be removed within 11 h under the optimum conditions (30 °C, pH 7.0) with an average degradation rate of 23.6 mg L^-1 h^-1, which was the highest one in literature so far. The silicone particles were added as the non-aqueous phases (NAP) to enhance the performance of MT degradation. The results indicated that the maximum degradation rate and specific cell growth of strain SJ-1 were 2.36 times and 1.31 times by Haldane kinetic model analysis in the NAP added test. The SO₄^2- was identified as the major intermediate and CO₂ as a final product in MT biodegradation. Overall, this is the first report that a newly isolated Pseudomonas sp. could use high concentration MT as sole energy source and carbon source and its activity could be enhanced by adding NAP. The results provide a suggestion for the development of more effective and reliable biological treatment processes.

Soil properties affect vapor-phase adsorption to regulate dimethyl disulfide diffusion in soil

Dimethyl disulfide (DMDS) is efficacious against nematodes and other soil-borne pathogens known to reduce crop quality and yield. Previous studies reported inconsistent efficacy and suggested that the diffusion of DMDS varied with different soil types. The effect of soil adsorption on gaseous DMDS diffusion through different soil types is poorly understood. To clarify the role and mechanism of soil adsorption in the diffusion of gaseous DMDS in soil, we have studied the diffusion rate constant (R_t) of gaseous DMDS in soils using a soil column experiment. The adsorption of DMDS at each gas-soil, soil-water and gas-water partition was measured by a batch-equilibrium headspace method. The results showed the DMDS adsorption equilibrium was well-described by the nonlinear Freundlich isotherm and the linear Henry isotherm. R_t values were strongly negatively correlated with the Henry coefficient (K_d) values. The K_d values of dry soil were several orders of magnitude higher than those observed in moist soil within each moisture content range. The K_d values in dry soil were strongly positively correlated with soil pore size (<2 nm). However, when the soil moisture content ranged from 3 to 12% (w/w), the K_d values were strongly correlated with specific surface area (SSA). Elevated temperatures promoted the gaseous phase of DMDS (consistent with Henry's Law) and its diffusion through soil. The soil-water partition coefficient (K'_f) ranged from 1.83 to 2.20 μg^11/n mL^1/n g^-1 in tested soils. Our results suggest that the DMDS vapor-phase diffusion in soil was significantly affected by soil adsorption, which in turn depended on the soil's properties especially the SSA and soil moisture content. These findings suggest applicators can reduce the risk of unsatisfactory and inconsistent efficacy results against soil-borne pests by adjusting the DMDS dose and fumigation period according to soil type, moisture conditions, and other environmental factors.

Off-Flavor Removal from Sheep Placenta via Fermentation with Novel Yeast Strain Brettanomyces deamine kh3 Isolated from Traditional Apple Vinegar

Animal placentae can be used as health-promoting food ingredients with various therapeutic efficacies, but their use is limited by their unpleasant odor and taste. This study aimed to investigate the possibility of deodorization of sheep placenta via yeast fermentation. A yeast strain was successfully isolated and identified as a novel Brettanomyces strain (Brettanomyces deamine kh3). The deodorizing efficacy of fermentation of the sheep placenta with B. deamine kh3 was evaluated by 42 panels, based on evaluation of preference, ranking, and aroma profiles, and compared with normal placenta and placenta fermented with B. bruxellensis. The results of the sensory evaluation indicated that fermentation of the sheep placenta with B. deamine kh3 may improve its palatability by increasing flavors such as that of grass (tree), rubber, and burnt, and by decreasing the odor and soy sauce flavor. Solid-phase microextraction-gas chromatography (SPME-GC) showed that major off-flavors in sheep placenta, such as ammonia, dimethyl disulfide, and 1,3-dioxolane, were completely diminished in the sheep placenta fermented with B. deamine kh3. This study presents those major volatile compounds, including 2-isobutyl\-4,4-dimethyl-1,3-dioxane, and 3-methyl-1-butanol, could be crucial in improving the palatability of the sheep placentae fermented with B. deamine kh3. This study provides a good starting point for the industrial application of a new deodorization method.

2-Hydroxypropyl-β-cyclodextrin encapsulates dimethyl disulfide producing a controlled release formulation

Dimethyl disulfide (DMDS), a soil fumigant, is an effective, broad-spectrum compound that often replaces bromomethane (MB) in the prevention and treatment of soil-borne diseases. However, the disadvantages of DMDS include toxicity, volatility, pungent odor, risk of human exposure, and environmental pollution. Cyclodextrin (CD) has been widely used as a carrier of chemicals in many industries due to its functional advantages and safety. In this study, a DMDS-controlled release formulation was developed by encapsulating DMDS in the cavity of 2-hydroxypropyl-β-cyclodextrin (HP-β-CD). This formulation reduced DMDS usage and production costs. Orthogonal experimental design, Fourier transform infrared (FT-IR), Scanning electron microscopy (SEM), Thermal gravity analysis (TGA) characterization, efficacy comparison, safety, and other aspects of the evaluation showed that under the best preparation conditions, the encapsulation rate was 81.49%. The efficacy of DMDS@HP-β-CD was similar to unformulated DMDS. The efficacy duration of the formulation was about two times longer than DMDS, and it was safer to use. This study reveals a cyclodextrin-DMDS formulation with reduced toxicity, longer duration, environmental safety and sustainability.

UV-activated adsorbents as novel materials for enhanced removal of malodorous gases

The performance of UV-activated Fe₂O₃-containing ZSM-5 (UFZ5) and silica (UFS) as adsorbents for the removal of low concentration of volatile organic sulfur compounds (VOSCs) was investigated in ambient conditions. A ∼99.9% and ∼89.2% removal of 10 ppm DMDS was observed for UFZ5 and UFS, respectively, due to a higher proportion of iron in UFZ5. The N₂ adsorption isotherm confirmed an unpredictable increase in the surface area and pore volume of adsorbents after the fifth adsorption-oxidation cycle, which made adsorbents highly reusable for multiple cycles. The spectroscopic analysis predicted an increase in the hydroxyl density along with the resistance of catalytic sites against sulfur deactivation, which favored the adsorption-oxidation process. The adsorption capacity of UFZ5 remained in the range of 0.12-0.22, 0.26-0.48, 0.40-0.75 mg g^-1 for methyl mercaptan (MM), dimethyl sulfide (DMS), and dimethyl disulfide (DMDS), respectively which were significantly higher than those calculated for UFS. The analysis confirmed SO₂, CO, CH₃OH, H₂O, and elemental S as by-products. The UFZ5 was found competent and robust for the treatment of VOSCs-contaminated indoor air.

Experimental study on volatile sulfur compound inhibition using a single-chamber membrane-free microbial electrolysis cell

Odor emissions from sewer systems and wastewater treatment plants have attracted much attention due to the potential negative effects on human health. A single-chamber membrane-free microbial electrolysis cell was proposed for the removal of sulfides in a sewer system. The feasibility of the use of volatile sulfur compounds and their removal efficiency in liquid and headspace gas phases were investigated using synthetic wastewater with real sewer sediment and Ru/Ir-coated titanium electrodes. The results indicate that hydrogen sulfide and volatile organic sulfur compounds were effectively inhibited in the liquid phase upon electrochemical treatment at current densities of 1.55, 2.06, and 2.58 mA/cm², and their removal rates reached up to 86.2-100%, except for dimethyl trisulfide, the amount of which increased greatly at 1.55 mA/cm². In addition, the amount of volatile sulfur compounds in the headspace decreased greatly; however, the total theoretical odor concentration was still high, and methanethiol and ethanethiol greatly contributed to the total strength of the odor concentration due to their low odor threshold concentrations. The major pathway for sulfide removal in the single-chamber membrane-free microbial electrolysis cell is biotic oxidation, the removal rate of which was 0.4-0.5 mg/min, 4-5 times that of indirect electrochemical oxidation.

Sulfur dioxide and o-xylene co-treatment in biofilter: Performance, bacterial populations and bioaerosols emissions

Sulfur dioxide (SO₂) and benzene homologs are frequently present in the off-gas during the process of sewage sludge drying. A laboratory scale biofilter was set up to co-treat SO₂ and o-xylene in the present study. SO₂ and o-xylene could be removed simultaneously in a single biofilter. Their concentration ratio in the inlet stream influenced the removal efficiencies. It is worth noting that the removal of SO₂ could be enhanced when low concentrations of o-xylene were introduced into the biofilter. Pseudomonas sp., Paenibacillus sp., and Bacillus sp. were the main functional bacteria groups in the biofilter. Sulfur-oxidizing bacteria (SOB) and o-xylene-degrading bacteria (XB) thrived in the biofilter and their counts as well as their growth rate increased with the increase in amount of SO₂ and o-xylene supplied. The microbial populations differed in counts and species due to the properties and components of the compounds being treated in the biofilter. The presence of mixed substrates enhanced the diversity of the microbial population. During the treatment process, bioaerosols including potentially pathogenic bacteria, e.g., Acinetobacter lwoffii and Aeromonas sp., were emitted from the biofilter. Further investigation is needed to focus on the potential hazards caused by the bioaerosols emitted from waste gas treatment bioreactors.

UV-Photochemistry of the Disulfide Bond: Evolution of Early Photoproducts from Picosecond X-ray Absorption Spectroscopy at the Sulfur K-Edge

We have investigated dimethyl disulfide as the basic moiety for understanding the photochemistry of disulfide bonds, which are central to a broad range of biochemical processes. Picosecond time-resolved X-ray absorption spectroscopy at the sulfur K-edge provides unique element-specific insight into the photochemistry of the disulfide bond initiated by 267 nm femtosecond pulses. We observe a broad but distinct transient induced absorption spectrum which recovers on at least two time scales in the nanosecond range. We employed RASSCF electronic structure calculations to simulate the sulfur-1s transitions of multiple possible chemical species, and identified the methylthiyl and methylperthiyl radicals as the primary reaction products. In addition, we identify disulfur and the CH₂S thione as the secondary reaction products of the perthiyl radical that are most likely to explain the observed spectral and kinetic signatures of our experiment. Our study underscores the importance of elemental specificity and the potential of time-resolved X-ray spectroscopy to identify short-lived reaction products in complex reaction schemes that underlie the rich photochemistry of disulfide systems.

Characterization of Bacterial Communities Associated with the Tyrian Purple Producing Gland in a Marine Gastropod

Dicathais orbita is a marine mollusc recognised for the production of anticancer compounds that are precursors to Tyrian purple. This study aimed to assess the diversity and identity of bacteria associated with the Tyrian purple producing hypobranchial gland, in comparison with foot tissue, using a high-throughput sequencing approach. Taxonomic and phylogenetic analysis of variable region V1-V3 of 16S rRNA bacterial gene amplicons in QIIME and MEGAN were carried out. This analysis revealed a highly diverse bacterial assemblage associated with the hypobranchial gland and foot tissues of D. orbita. The dominant bacterial phylum in the 16S rRNA bacterial profiling data set was Proteobacteria followed by Bacteroidetes, Tenericutes and Spirochaetes. In comparison to the foot, the hypobranchial gland had significantly lower bacterial diversity and a different community composition, based on taxonomic assignment at the genus level. A higher abundance of indole producing Vibrio spp. and the presence of bacteria with brominating capabilities in the hypobranchial gland suggest bacteria have a potential role in biosynthesis of Tyrian purple in D. orbita.

Aerobic biodegradation of odorous dimethyl disulfide in aqueous medium by isolated Bacillus cereus GIGAN2 and identification of transformation intermediates

A novel, flagellated, rod-shape, Gram-positive facultative aerobe, was isolated and identified as Bacillus cereus GIGAN2. It can effectively remove model odorous organics dimethyl disulfide (DMDS) in aqueous solution under aerobic conditions. Initial concentration, pH value and temperature played important role in DMDS biodegradation, and up to 100% of 10mgL(-1) of DMDS could be removed within 96h under the optimum conditions (30°C, pH 7.0 and 200rpm) with a maximum biodegradation rate constant of 0.0330h(-1) and minimum half-life of 21.0h, respectively. Three main intermediates were identified using gas chromatography-mass spectrometry during this biodegradation process. Further, a reaction scheme is also proposed to explain the possible DMDS biodegradation mechanism by GIGAN2 based on the above-identified intermediates. Overall, this is the first report to demonstrate a newly isolated strain using high concentrated DMDS as the sole carbon and energy source with high efficiency.

Dimethyl sulfide biofiltration using immobilized Hyphomicrobium VS and Thiobacillus thioparus TK-m in sugarcane bagasse

Sugarcane bagasse was used as a carrier material of microorganisms in two different biofilters used to remove dimethyl sulfide (DMS) from a gas stream. The first biofilter was inoculated with Hyphomicrobium VS and the second with Thiobacillus thioparus Tk-m. During the operation of the biofilters the empty bed residence time (EBRT) was varied from 90 to 180 seconds and the inlet concentration of DMS from 12 to 50 ppmv. The inlet load was varied in the range of 0.62 to 5.2 (g DMS/m3 h). The maximum elimination capacity (EC) of the biofilter inoculated with Hyphomicrobium VS was 5 g DMS/m3 h; however, for the biofilter inoculated with T. thioparus Tk-m the maximum EC was 3.9 g DMS/m3 h. For T. thioparus TK-m the maximum removal efficiency (RE) obtained was 85.1 +/- 5.2% at 12 ppmv DMS inlet concentration, inlet load of 0.62 g DMS/m3 h and 180 s EBRT. The highest removal efficiency for Hyphomicrobium VS was 97.6 + 4.8% at 12 ppmv DMS inlet concentration, load of 0.62 g DMS/m3 h and 180 s EBRT.

Resistance and resilience of removal efficiency and bacterial community structure of gas biofilters exposed to repeated shock loads

Since full-scale biofilters are often operated under fluctuating conditions, it is critical to understand their response to transient states. Four pilot-scale biofilters treating a composting gas mixture and undergoing repeated substrate pulses of increasing intensity were studied. A systematic approach was proposed to quantify the resistance and resilience capacity of their removal efficiency, which enabled to distinguish between recalcitrant (ammonia, DMDS, ketones) and easily degradable (esters and aldehyde) compounds. The threshold of disturbing shock intensity and the influence of disturbance history depended on the contaminant considered. The spatial and temporal distribution of the bacterial community structure in response to the perturbation regime was analysed by Denaturing Gradient Gel Electrophoresis (DGGE). Even if the substrate-pulses acted as a driving force for some community characteristics (community stratification), the structure-function relationships were trickier to evidence: the distributions of resistance and composition were only partially coupled, with contradictory results depending on the contaminant considered.

Comparison of the removal of ethanethiol in twin-biotrickling filters inoculated with strain RG-1 and B350 mixed microorganisms

This study aims to compare the biological degradation performance of ethanethiol using strain RG-1 and B350 commercial mixed microorganisms, which were inoculated and immobilized on ceramic particles in twin-biotrickling filter columns. The parameters affecting the removal efficiency, such as empty bed residence time (EBRT) and inlet concentration, were investigated in detail. When EBRT ranged from 332 to 66 s at a fixed inlet concentration of 1.05 mg L(-1), the total removal efficiencies for RG-1 and B350 both decreased from 100% to 70.90% and 47.20%, respectively. The maximum elimination capacities for RG-1 and B350 were 38.36 (removal efficiency=89.20%) and 25.82 g m(-3) h(-1) (removal efficiency=57.10%), respectively, at an EBRT of 83 s. The variation of the inlet concentration at a fixed EBRT of 110 s did not change the removal efficiencies which remained at 100% for RG-1 and B350 at concentrations of less than 1.05 and 0.64 mg L(-1), respectively. The maximum elimination capacities were 39.93 (removal efficiency=60.30%) and 30.34 g m(-3) h(-1) (removal efficiency=46.20%) for RG-1 and B350, respectively, at an inlet concentration of 2.03 mg L(-1). Sulfate was the main metabolic product of sulfur in ethanethiol. Based the results, strain RG-1 would be a better choice than strain B350 for the biodegradation of ethanethiol.

Organization of Pseudomonas fluorescens on chemically different nano/microstructured surfaces

This paper describes bacterial organization on nano/micropatterned surfaces with different chemical properties, which show different interactions with the biological systems (inert, biocompatible, and bactericide). These surfaces were prepared by molding techniques and exposed to Pseudomonas fluorescens (P. fluorescens) cultures. Results from atomic force microscopy and optical imaging demonstrate that the structure of P. fluorescens aggregates is strongly dependent on the surface topography while there is no clear linking with the physical-chemical surface properties (charge and contact angle) of the substrate immersed in abiotic culture media. We observe that regardless of the material when the surface pattern matches the bacterial size, bacterial assemblages involved in surface colonization are disorganized. The fact there is not a relationship between surface chemistry and bacterial organization can be explained by the coverage of the surfaces by adsorbed organic species coming from the culture medium. Viability assays indicate that copper behaves as a toxic substrate despite the presence of adsorbed molecules. The combination of surface traps and biocidal activity could act synergistically as a suitable strategy to limit bacterial spreading on implant materials.

Inhibition of microbiological sulfide oxidation by methanethiol and dimethyl polysulfides at natron-alkaline conditions

To avoid problems related to the discharge of sulfidic spent caustics, a biotechnological process is developed for the treatment of gases containing both hydrogen sulfide and methanethiol. The process operates at natron-alkaline conditions (>1 mol L⁻¹ of sodium- and potassium carbonates and a pH of 8.5–10) to enable the treatment of gases with a high partial CO₂ pressure. In the process, methanethiol reacts with biologically produced sulfur particles to form a complex mixture predominantly consisting of inorganic polysulfides, dimethyl disulfide (DMDS), and dimethyl trisulfide (DMTS). The effect of these organic sulfur compounds on the biological oxidation of sulfide to elemental sulfur was studied with natron-alkaliphilic bacteria belonging to the genus Thioalkalivibrio. Biological oxidation rates were reduced by 50% at 0.05 mM methanethiol, while for DMDS and DMTS, this was estimated to occur at 1.5 and 1.0 mM, respectively. The inhibiting effect of methanethiol on biological sulfide oxidation diminished due to its reaction with biologically produced sulfur particles. This reaction increases the feasibility of biotechnological treatment of gases containing both hydrogen sulfide and methanethiol at natron-alkaline conditions.

Microbial populations analysis and field application of biofilter for the removal of volatile-sulfur compounds from swine wastewater treatment system

A biofilter packed with granular activated carbon (GAC) was applied to eliminate volatile-sulfur compounds (VSC) emitted from solid-liquid separation tank in swine wastewater treatment system. Hydrogen sulfide, methanethiol, dimethyl disulfide, and dimethyl sulfide were effectively reduced to 96-100% at gas residence times of 13-30s. Elemental sulfur and sulfate are their primary oxidation metabolites. Regarding odor, an average of 86% reduction was achieved at short residence time (13s). In addition, bioaerosol emissions could also be effectively reduced by 90% with the biofilter. Advantages of the system include low moisture demand, low pressure drop, and high biofilm stability. Further characterization of bacterial populations of the activated carbon samples using the fluorescent in situ hybridization (FISH) technique revealed that Pseudomonas sp. remained the predominant community (56-70%) after long-term evaluation of 415 days.