2-bromoethanesulfonic Acid Research Articles

Reducing methane production from rumen cultures by bioaugmentation with homoacetogenic bacteria

Methane from anaerobic fermentation in the rumen of cattle is a major contributor to greenhouse gases (50–60%). Methanogenesis is an important process in the ruminants as it scavenges hydrogen produced during the anaerobic fermentation of sugars in the rumen and, thereby, balances the fermentation process. This work focuses on mitigation of methane production in rumen by bioaugmentation with hydrogenotrophic acetogenic strains thus, channelizing hydrogen towards acetate instead of methane. For this two acetogenic cultures: Acetobacterium woodii and a stable consortium from a baby kangaroo feces sample were used as potential competitors for hydrogen-carbon dioxide against rumen methanogens. Addition of Acetobacterium woodii or an acetogenic kangaroo consortium had only limited effect on methane production from continuously grown rumen cultures. However, one-time treatment with an inhibitor of methanogenesis (2-bromoethanesulfonic acid), along with addition of either of the two acetogenic cultures resulted in well-functioning fermentation process with acetogenesis with no methane production. Monod's growth kinetics studies were done to test the ability of selected homoacetogens to compete against methanogens for hydrogen. The results show a lower Ks value for the methanogenic culture (0.737 mM hydrogen) compared to the Ks values for Acetobacterium woodii and the kangaroo consortia of 6.844 mM and 3.788 mM hydrogen, respectively. The Vmax was found to be similar for the methanogenic and kangaroo culture (0.381 mM/h and 0.331 mM/h, respectively) but lower for Acetobacterium woodii (0.217 mM/h).

Selective enrichment of mixed consortia towards enhanced 1,3-Propanediol production from glycerol

Glycerol fermentation using mixed consortia leads to the production of several bio-products such as 1,3-Propanediol (1,3-PDO), acetate, lactate, ethanol, butyrate, propionate and biogas. Increasing production specificity majorly of 1,3-PDO in glycerol fermentation was assessed by suppressing 1,3-PDO non-producing microbial communities. Dual pretreatment (selective enrichment) strategy employing heat-shock and 2-bromoethanesulfonic acid (BESA) was implemented to enhance 1,3-PDO productivity. Additionally, Vitamin B12 (Vit. B12) was supplemented for improving fermentation efficiency considering its role in glycerol fermentation. 1,3-PDO (9.3 ± 0.51 g/L; 0.64 mol1,3-PDO/molGly_con) was the major product from 20 g/L glycerol in the system (RHHBVS) operated with combining enrichment strategy and Vit. B12 supplementation compared to control (RHHS) system (5.56 ± 0.26 g/L; 0.48 mol1,3-PDO/molGly_con) operated solely with the heat-shock pretreatment strategy. Acetate was major co-metabolite in all the systems and highest was observed with RHHBVS (1.45 ± 0.72 g/L) system. The results supported the positive impact of selective enrichment strategy (dual pretreatment of inoculum) towards the enhanced 1,3-PDO production.

Microbial Communities Associated with Methylmercury Degradation in Paddy Soils.

Bioaccumulation of the neurotoxin methylmercury (MeHg) in rice has raised worldwide concerns because of its risks to human health. Certain microorganisms are able to degrade MeHg in pure cultures, but the roles and diversities of the microbial communities in MeHg degradation in rice paddy soils are unknown. Using a series of microcosms, we investigated MeHg degradation in paddy soils from Hunan, Guizhou, and Hubei provinces, representing three major rice production regions in China, and further characterized one of the soils from the Hunan Province for microbial communities associated with MeHg degradation. Microbial demethylation was observed in all three soils, demonstrated by significantly more MeHg degraded in the unsterilized soils than in the sterilized controls. More demethylation occurred in water-saturated soils than in unsaturated soils, but the addition of molybdate and bromoethanesulfonic acid as the respective inhibitors of sulfate reducing bacteria and methanogens showed insignificant effects on MeHg degradation. However, the addition of Cu enhanced MeHg degradation and the enrichment of Xanthomonadaceae in the unsaturated soil. 16S rRNA Illumina sequencing and metatranscriptomic analyses of the Hunan soil consistently revealed that Catenulisporaceae, Frankiaceae, Mycobacteriaceae, and Thermomonosporaceae were among the most likely microbial taxa in influencing MeHg degradation in the paddy soil, and they were confirmed by combined analyses of the co-occurrence network, random forest modeling, and linear discriminant analysis of the effect size. Our results shed additional light onto the roles of microbial communities in MeHg degradation in paddy soils and its subsequent bioaccumulation in rice grains.

Azo dye biotransformation mediated by AQS immobilized on activated carbon cloth in the presence of microbial inhibitors

In this work, anthraquinone-2-sulfonate (AQS) was covalently immobilized onto activated carbon cloth (ACC), to be used as redox mediator for the reductive decolorization of reactive red 2 (RR2) by an anaerobic consortium. The immobilization of AQS improved the capacity of ACC to transfer electrons, evidenced by an increment of 3.29-fold in the extent of RR2 decolorization in absence of inhibitors, compared to incubations lacking AQS. Experiments conducted in the presence of vancomycin, an inhibitor of acidogenic bacteria, and with 2-bromoethane sulfonic acid (BES), an inhibitor of methanogenic archaea, revealed that acidogenic bacteria are the main responsible for RR2 biotransformation mediated by immobilized AQS. Nonetheless, the results also suggest that some methanogens are able to maintain their capacity to use immobilized AQS as an electron acceptor to sustain the decolorization process, even in the presence of BES.

Effect of Graded Levels of Bromoethanesulfonic Acid Supplementation on Methane Production, Rumen Microbial Diversity and Fermentation Characteristics

Bromoethanesulfonic acid (BES) was examined as a methane inhibitor and its impact on rumen microbial populations in male cattle calves. Ten crossbred cattle calves (average body weight, 132±2 kg) were divided into two groups of five each and were fed on a diet containing 19.9% CP and 72.6% TDN. In the experimental group, BES was fed at the rate of 5 mg for first 10 days, 10 mg for next 10 days (11–20th day) and 15 mg/kg BW for another 10 days (21 to 30th days) of the experiment. Rumen liquor was collected by stomach tube from calves after feeding of each level of BES and was used for studying the microbial profile by real time PCR and as an inoculum for in vitro gas production test. The in vitro methane production (ml/g DDM) was reduced (P<0.05) by 35, 8.1 and 15 per cent on feeding BES at the levels of 5, 10 and 15 mg/kg BW (P<0.001, P=0.007 and P=0.009, respectively). The in vitro true digestibility of feed was not affected at lower levels but was significantly improved at 15 mg BES level (P=0.026). The population of protozoa, was significantly reduced at 5 mg BES (P=0.014) level but at 10 mg level, fungi and methanogens were reduced significantly (P=0.031, P=0.034) and at 15 mg BES level only fungal population was reduced (P=0.029). The results indicated that BES can reduce rumen methanogenesis but cannot eliminate methanogens completely from the rumen.

Biomethanation of blast furnace gas using anaerobic granular sludge via addition of hydrogen.

The high concentrations of CO (toxic) and CO2 (greenhouse gases) in blast furnace gas (a by-product of steelworks) reflect its low calorific value. In this study, anaerobic granular sludge was used to convert carbon from blast furnace gas to methane via exogenous hydrogen addition. The inhibition of methane production by CO partial pressure (PCO) was found to start from 0.4 atm. The intermediate metabolites from CO to methane including acetate, propionate, and H2 accumulated at higher CO concentrations in the presence of 2-bromoethanesulfonic acid. After the introduction of H2 and blast furnace gas, although the hydrogen partial pressure (PH2) up to 1.54 atm resulted in the maximum CH4 yield, the whole system was not stable due to the accumulation of a large amount of volatile fatty acids. The optimum PH2 on CH4 production from the simulated blast furnace gas, 5.32 mmol g−1 VSS, was determined at 0.88 atm in this study.

Changes in Glucose Fermentation Pathways as a Response to the Free Ammonia Concentration in Microbial Electrolysis Cells.

When a mixed-culture microbial electrolysis cell (MEC) is fed with a fermentable substrate, such as glucose, a significant fraction of the substrate's electrons ends up as methane (CH4) through hydrogenotrophic methanogenesis, an outcome that is undesired. Here, we show that free ammonia-nitrogen (FAN, which is NH3) altered the glucose fermentation pathways in batch MECs, minimizing the production of H2, the "fuel" for hydrogenotrophic methanogens. Consequently, the Coulombic efficiency (CE) increased: 57% for 0.02 g of FAN/L of fed-MEC, compared to 76% for 0.18 g of FAN/L of fed-MECs and 62% for 0.37 g of FAN/L of fed-MECs. Increasing the FAN concentration was associated with the accumulation of higher organic acids (e.g., lactate, iso-butyrate, and propionate), which was accompanied by increasing relative abundances of phylotypes that are most closely related to anode respiration (Geobacteraceae), lactic-acid production (Lactobacillales), and syntrophic acetate oxidation (Clostridiaceae). Thus, the microbial community established syntrophic relationships among glucose fermenters, acetogens, and anode-respiring bacteria (ARB). The archaeal population of the MEC fed 0.02 g FAN/L was dominated by Methanobacterium, but 0.18 and 0.37 g FAN/L led to Methanobrevibacter becoming the most abundant species. Our results provide insight into a way to decrease CH4 production and increase CE using FAN to control the fermentation step, instead of inhibiting methanogens using expensive or toxic chemical inhibitors, such as 2-bromoethanesulfonic acid.

Biomethanation of Syngas Using Anaerobic Sludge: Shift in the Catabolic Routes with the CO Partial Pressure Increase.

Syngas generated by thermal gasification of biomass or coal can be steam reformed and purified into methane, which could be used locally for energy needs, or re-injected in the natural gas grid. As an alternative to chemical catalysis, the main components of the syngas (CO, CO2, and H2) can be used as substrates by a wide range of microorganisms, to be converted into gas biofuels, including methane. This study evaluates the carboxydotrophic (CO-consuming) methanogenic potential present in an anaerobic sludge from an upflow anaerobic sludge bed (UASB) reactor treating waste water, and elucidates the CO conversion routes to methane at 35 ± 3°C. Kinetic activity tests under CO at partial pressures (pCO) varying from 0.1 to 1.5 atm (0.09–1.31 mmol/L in the liquid phase) showed a significant carboxydotrophic activity potential for growing conditions on CO alone. A maximum methanogenic activity of 1 mmol CH4 per g of volatile suspended solid and per day was achieved at 0.2 atm of CO (0.17 mmol/L), and then the rate decreased with the amount of CO supplied. The intermediary metabolites such as acetate, H2, and propionate started to accumulate at higher CO concentrations. Inhibition experiments with 2-bromoethanesulfonic acid (BES), fluoroacetate, and vancomycin showed that in a mixed culture CO was converted mainly to acetate by acetogenic bacteria, which was further transformed to methane by acetoclastic methanogens, while direct methanogenic CO conversion was negligible. Methanogenesis was totally blocked at high pCO in the bottles (≥1 atm). However it was possible to achieve higher methanogenic potential under a 100% CO atmosphere after acclimation of the sludge to CO. This adaptation to high CO concentrations led to a shift in the archaeal population, then dominated by hydrogen-utilizing methanogens, which were able to take over acetoclastic methanogens, while syntrophic acetate oxidizing (SAO) bacteria oxidized acetate into CO2 and H2. The disaggregation of the granular sludge showed a negative impact on their methanogenic activity, confirming that the acetoclastic methanogens were the most sensitive to CO, and a contrario, the advantage of using granular sludge for further development toward large-scale methane production from CO-rich syngas.

Impact of undissociated volatile fatty acids on acidogenesis in a two-phase anaerobic system

This study investigated the degradation and production of volatile fatty acids (VFAs) in the acidogenic phase reactor of a two-phase anaerobic system. 20mmol/L bromoethanesulfonic acid (BESA) was used to inhibit acidogenic methanogens (which were present in the acidogenic phase reactor) from degrading VFAs. The impact of undissociated volatile fatty acids (unVFAs) on “net” VFAs production in the acidogenic phase reactor was then evaluated, with the exclusion of concurrent VFAs degradation. “Net” VFAs production from glucose degradation was partially inhibited at high unVFAs concentrations, with 59%, 37% and 60% reduction in production rates at 2190mg chemical oxygen demand (COD)/L undissociated acetic acid (unHAc), 2130mg COD/L undissociated propionic acid (unHPr) and 2280mg COD/L undissociated n-butyric acid (unHBu), respectively. The profile of VFAs produced further indicated that while an unVFA can primarily affect its own formation, there were also unVFAs that affected the formation of other VFAs.

Dark fermentation of complex waste biomass for biohydrogen production by pretreated thermophilic anaerobic digestate

The Biohydrogen Potential (BHP) of six different types of waste biomass typical for the Campania Region (Italy) was investigated. Anaerobic sludge pre-treated with the specific methanogenic inhibitor sodium 2-bromoethanesulfonic acid (BESA) was used as seed inoculum. The BESA pre-treatment yielded the highest BHP in BHP tests carried out with pre-treated anaerobic sludge using potato and pumpkin waste as the substrates, in comparison with aeration or heat shock pre-treatment. The BHP tests carried out with different complex waste biomass showed average BHP values in a decreasing order from potato and pumpkin wastes (171.1 ± 7.3 ml H2/g VS) to buffalo manure (135.6 ± 4.1 ml H2/g VS), dried blood (slaughter house waste, 87.6 ± 4.1 ml H2/g VS), fennel waste (58.1 ± 29.8 ml H2/g VS), olive pomace (54.9 ± 5.4 ml H2/g VS) and olive mill wastewater (46.0 ± 15.6 ml H2/g VS). The digestate was analyzed for major soluble metabolites to elucidate the different biochemical pathways in the BHP tests. These showed the H2 was produced via mixed type fermentation pathways.

Ethane- and propane-producing potential and molecular characterization of an ethanogenic enrichment in an anoxic estuarine sediment

Ethane and propane are low molecular weight hydrocarbons observed widely at trace levels in cold marine sediments where thermogenic sources are considered insignificant, but their biological sources remain poorly constrained. In this study, several C2 and C3 compounds including alkenes, alcohols, thiols and carboxylic acids with a C2 or C3 skeleton were tested for their relative alkane-producing potential in an anoxic estuary sediment. Maximum conversion efficiency of substrates to ethane or propane was observed in the sediment supplemented with ethylene (up to 38%), followed by additions with ethanethiol (0.01%) and propanethiol (0.003%). Experiments with sterilized sediment, 2-bromoethanesulfonic acid or NaNO3 were negative for alkane production, suggesting that methanogens were involved in alkane generation. Detailed investigation on ethanogenesis from ethylene showed that this reaction required H2 but at reasonably low concentration (< 120nmol dissolved H2 l−1 slurry) and caused a slight stable carbon isotope effect (εethane/ethylene=−8.6±2.4‰). The high ethane-producing potential, reasonable H2 requirement and extensive occurrence of ethylene make ethylene reduction a plausible explanation for ethane in cold marine sediment. Phylogenetic analysis was first carried out with an ethane-producing enrichment with ethylene as the substrate and showed a dominance of homoacetogenic bacteria and the methanogenic genus Methanocalculus. Although we cannot rule out the possibility that other methanogens in the gene libraries are responsible for ethanogenesis from ethylene, the dominance of Methanocalculus, with its hydrogenotrophic cultured representatives, is in accord with our biogeochemical observation that H2 is required for this reaction.

Recovery of Methanogenesis Following Summer Drought in Soils from Two Cool Temperate Peatlands, New York State, USA

Following a summer drought, intact cores of peat soil from two cool temperate peatlands (a rain-fed bog and a groundwater-fed swamp) were exposed experimentally to three different water table levels. The goal was to examine recovery of anaerobic methanogenesis and to evaluate peat soil decomposition to methane (CH4), carbon dioxide (CO2), and dissolved organic carbon (DOC) upon rewetting. Methane emission from soils to the atmosphere was greatest (mean = 80 μmol m−2 s−1) when the entire peat core was rewetted quickly; emission was negligible at low water level and when peat cores were rewetted gradually. Rates of CO2 emission (mean = 1.0 μmol m−2 s−1) were relatively insensitive to water level. Concentrations of CH4 in soil air spaces suggest that onset of methanogenesis induces, but later represses, aerobic oxidation of CH4 above the water table. Concentrations of CO2 suggest production at the soil surface of swamp peat versus at greater depths in bog peat. Portions of peat soil incubated in vitro without oxygen (O2) exhibited a lag before the onset of methanogenesis, and the lag time was less in peat from the cores rewetted quickly. The inhibition of methanogenesis by the selective inhibitor 2-bromoethanesulfonic acid (BES) decreased CO2 production by 20 to 30% but resulted in an increase in concentrations of DOC by 2 to 5 times. The results show that methanogens in peat soils tolerate moderate drought, and recovery varies among different peat types. In peat soils, the inhibition of methanogenesis might enhance DOC availability.

할로겐 화합물의 첨가가 반추위 발효성상과 메탄생성에 미치는 영향

본 연구는 할로겐 화합물의 첨가가 in vitro 상의 반추위 발효성상과 메탄생성에 미치는 영향에 대한 효과를 규명하고자 실시하였다. Italian rye grass 및 배합사료를 6:4의 비율로 급여한 반추위 cannula가 시술된 홀스타인에서 반추위액을 채취하여 사용하였고, 채취된 반추위액은 분쇄된 timothy (대조구; C)에 bromochloromethane (BCM구), 2-Bromoethanesulfonic acid (BES구), 3-Bromopropanesulfonic acid (BPS구), chloroform (CLF구) 및 Pyromellitic diimide (PMDI구)의 5가지 할로겐 화합물을 각각 1 ppm씩 첨가하여 in vitro 배양하였다. pH는 6.72에서 6.25 정도로 배양시간이 경과함에 따라 낮아지는 경향을 나타내었고, 배양 48시간에는 처리구간 차이가 없었다. 배양 48시간 후의 총 가스 발생량은 처리구간 유의적인(p<0.05) 차이는 없었고, BPS구를 제외한 모든 처리구에서의 메탄 발생량은 대조구에 비해 유의적으로(p<0.05) 감소하였다. 배양 12시간에서의 총 휘발성 지방산 및 propionic acid의 발생량은 처리구가 대조구에 비해 유의적으로(p<0.05) 높았다. 본 실험의 결과, 할로겐 화합물의 첨가는 반추위 내의 pH, 건물 소화율, 미생물 수 및 총 가스 발생량의 발효 성상에는 영향을 주지 않으면서 메탄의 발생량이 감소 되었다. 실험 결과를 종합해 보면, 할로겐 화합물 첨가는 반추위 내 pH, 가스 발생량, 반추위 미생물 성장량 및 propionic acid 모두 증가하였으며, 반추위내 메탄생성을 억제하였다. 앞으로 할로겐화합물과 다른 메탄억제 물질과 혼합하여 반추위 내 메탄생성 억제에 관한 구체적인 연구가 필요한 것으로 생각된다. This study was conducted to evaluate effects of halogenated compounds on in vitro rumen fermentation characteristics and methane emissions. A fistulated Holstein cow of 650 kg body weight was used as a donor of rumen fluid. Five kinds of halogenated compounds (bromochloromethane (BCM), 2-bromoethane sulfonic acid (BES), 3-bromopropanesulfonic acid (BPS), chloroform (CLF), and pyromellitic diimide (PMDI) known to inhibit methyl-coenzyme M reductase activity were added to an in vitro fermentation incubated with rumen fluid. The microbial population including bacteria, protozoa, and fungi were enumerated, and gas production including methane and fermentation characteristics were observed in vitro. The pH values ranged from 6.25 to 6.72 in all the treatments, and these showed a similar level at 48 hr. The total gas production in the treatments showed a similar pattern with C at 48 hr, whereas methane production in the treatments was lower (p<0.05) than C. Concentrations of total volatile fatty acids (VFAs) and propionic acid were higher (p<0.05) in the treatments than in C at 12 hr. Therefore, halogenated compounds (BCM, BES, BPS, CLF, and PMDI) inhibited in vitro methane emissions by inhibiting methanogens in the rumen. Further studies on safety are needed.

Electrosynthesis of Commodity Chemicals by an Autotrophic Microbial Community

A microbial community originating from brewery waste produced methane, acetate, and hydrogen when selected on a granular graphite cathode poised at -590 mV versus the standard hydrogen electrode (SHE) with CO(2) as the only carbon source. This is the first report on the simultaneous electrosynthesis of these commodity chemicals and the first description of electroacetogenesis by a microbial community. Deep sequencing of the active community 16S rRNA revealed a dynamic microbial community composed of an invariant Archaea population of Methanobacterium spp. and a shifting Bacteria population. Acetobacterium spp. were the most abundant Bacteria on the cathode when acetogenesis dominated. Methane was generally the dominant product with rates increasing from <1 to 7 mM day(-1) (per cathode liquid volume) and was concomitantly produced with acetate and hydrogen. Acetogenesis increased to >4 mM day(-1) (accumulated to 28.5 mM over 12 days), and methanogenesis ceased following the addition of 2-bromoethanesulfonic acid. Traces of hydrogen accumulated during initial selection and subsequently accelerated to >11 mM day(-1) (versus 0.045 mM day(-1) abiotic production). The hypothesis of electrosynthetic biocatalysis occurring at the microbe-electrode interface was supported by a catalytic wave (midpoint potential of -460 mV versus SHE) in cyclic voltammetry scans of the biocathode, the lack of redox active components in the medium, and the generation of comparatively high amounts of products (even after medium exchange). In addition, the volumetric production rates of these three commodity chemicals are marked improvements for electrosynthesis, advancing the process toward economic feasibility.

Methanogenic Octadecene Degradation by Syntrophic Enrichment Culture from Brackish Sediments

A microbial enrichment culture from brackish sediments was able to grow on octadec-1-ene (an unsaturated aliphatic hydrocarbon) as sole source of carbon and energy, under methanogenic conditions. Octadecene degradation is stopped either when bromoethanesulfonic acid, a selective inhibitor of methanogenesis is introduced, or when hydrogen is introduced. In the presence of bromoethanesulfonic acid, the degradation is restored by the addition of a hydrogenotrophic sulfate-reducing microorganism with sulfate. Results of molecular biodiversity, which revealed the presence of bacteria as well as of acetoclastic and hydrogenotrophic methanogens, are consistent with a syntrophic degradation involving Bacteria and Archaea. This is the first demonstration of syntrophic alkene degradation by microbial communities, showing that syntrophy is more widespread than we could have thought so far. These results highlight the need for a better understanding of microbial interactions and their role in the organic-matter degradation in polluted environments.

Humic acid addition lowers methane release in peats of the Mer Bleue bog, Canada

The effects of humic substances on methanogenesis in peats are poorly understood. In incubation experiments we added Pahokee Peat Humic Acid (DOM), a suppressor for methanogenesis (2-bromoethane sulfonic acid, BES), and BES + DOM to bog peat and studied CO2 and CH4 release. Addition of DOM lowered CH4 (p < 0.05) but not CO2 release compared to controls. BES addition suppressed CH4 release compared to controls (p < 0.01). DOM/BES addition lowered the release even further (p = 0.06) but did not induce net CH4 loss. DOM was thus utilized as electron acceptor and lowered CH4 release; anaerobic CH4 oxidation may have contributed to this effect.

Methanogens: Principal Methylators of Mercury in Lake Periphyton

Mercury methylation and demethylation rates were measured in periphyton biofilms growing on submerged plants from a shallow fluvial lake located along the St. Lawrence River (Quebec, Canada). Incubations were performed in situ within macrophytes beds using low-level spikes of (199)HgO and Me(200)Hg stable isotopes as tracers. To determine which microbial guilds are playing a role in these processes, methylation/demethylation experiments were performed in the absence and presence of different metabolic inhibitors: chloramphenicol (general bacteriostatic inhibitor), molybdate (sodium molybdate, a sulfate reduction inhibitor), BESA (2-bromoethane sulfonic acid, a methanogenesis inhibitor), and DCMU (3-(3,4-dichlorophenyl)-1,1 dimethyl urea, a photosynthesis inhibitor). Active microbes of the periphytic consortium were also characterized using 16S rRNA gene sequencing. Methylation rates in the absence of inhibitors varied from 0.0015 to 0.0180 d(-1) while demethylation rates ranged from 0.083 to 0.217 d(-1), which corresponds to a net methylmercury balance of -0.51 to 1.28 ng gDW periphyton(-1) d(-1). Methylation rates were significantly decreased by half by DCMU and chloramphenicol, totally inhibited by BESA, and were highly stimulated by molybdate. This suggests that methanogens rather than sulfate reducing bacteria were likely the primary methylators in the periphyton of a temperate fluvial lake, a conclusion supported by the detection of 16S rRNA gene sequences that were closely related to those of methanogens. This first clear demonstration of methanogens' role in mercury methylation in environmental periphyton samples expands the known diversity of microbial guilds that contribute to the formation of the neurotoxic substance methylmercury.

Reductive dechlorination of tetrachloroethene by two compost samples with different maturity

This study sets up microcosms using two types of compost samples, bagasse/manure compost, and yard-trimming compost with different maturity, to evaluate their capacity for reductive dechlorination of tetrachloroethene (PCE). The experimental results show that less matured compost samples could reduce 300μM of PCE to ethene within 180days of incubation. Decreasing initial PCE concentration and removing dissolved oxygen from the solution could enhance reducing efficiency. The solution remains near neutral pH throughout the experiment, and ethene emerged when the redox potential dropped to below −150mV. Different microbial inhibition agents, such as 2-bromoethanesulfonic acid and sodium molybdate 2-hydrate, exhibit different effects on the dechlorination efficiency. The potential advantages of using compost to remove PCE are discussed. Overall, due to their high carbon content, diverse microbial activity, high buffer capacity, and complex physical structure, compost samples could serve as suitable media for dechlorinating PCE.

Evidence for syntrophic butyrate metabolism under sulfate-reducing conditions in a hydrocarbon-contaminated aquifer

The importance of syntrophy in the degradation of butyrate in an aquifer where sulfate reduction was shown to be an important terminal electron-accepting process was assessed. Hydrocarbon-contaminated aquifer sediments coupled butyrate degradation to sulfate reduction and methane production. Butyrate degradation in methanogenic microcosms was inhibited by the addition of 2-bromoethanesulfonic acid, and was restored by the addition of 10 mM sulfate and a hydrogen- and formate-using sulfate reducer, but not by the addition of 10 mM sulfate alone. Molybdate addition inhibited butyrate degradation in sulfate-reducing microcosms. The addition of CO, which inhibits hydrogenases, to sulfate-reducing microcosms inhibited butyrate metabolism and caused the hydrogen partial pressure to increase to levels that would make syntrophic butyrate degradation via sulfate reduction energetically unfavorable (-5 to +3 kJ mol(-1) ). DNA extracted from the most probable number cultures and contaminated sediments contained sequences related to members of the families Syntrophomonadaceae and Syntrophaceae, whose members are known to syntrophically degrade fatty acids, as well as sequences related to uncultured Firmicutes, Desulfobulbaceae, Desulfobacteriaceae, and Desulfovibrionaceae. These data show that contaminated sediments degraded butyrate syntrophically coupled to methane production and sulfate reduction.

Biogenic hydrogen and methane production from Chlorella vulgaris and Dunaliella tertiolecta biomass

BackgroundMicroalgae are a promising feedstock for biofuel and bioenergy production due to their high photosynthetic efficiencies, high growth rates and no need for external organic carbon supply. In this study, utilization of Chlorella vulgaris (a fresh water microalga) and Dunaliella tertiolecta (a marine microalga) biomass was tested as a feedstock for anaerobic H2 and CH4 production.ResultsAnaerobic serum bottle assays were conducted at 37°C with enrichment cultures derived from municipal anaerobic digester sludge. Low levels of H2 were produced by anaerobic enrichment cultures, but H2 was subsequently consumed even in the presence of 2-bromoethanesulfonic acid, an inhibitor of methanogens. Without inoculation, algal biomass still produced H2 due to the activities of satellite bacteria associated with algal cultures. CH4 was produced from both types of biomass with anaerobic enrichments. Polymerase chain reaction-denaturing gradient gel electrophoresis profiling indicated the presence of H2-producing and H2-consuming bacteria in the anaerobic enrichment cultures and the presence of H2-producing bacteria among the satellite bacteria in both sources of algal biomass.ConclusionsH2 production by the satellite bacteria was comparable from D. tertiolecta (12.6 ml H2/g volatile solids (VS)) and from C. vulgaris (10.8 ml H2/g VS), whereas CH4 production was significantly higher from C. vulgaris (286 ml/g VS) than from D. tertiolecta (24 ml/g VS). The high salinity of the D. tertiolecta slurry, prohibitive to methanogens, was the probable reason for lower CH4 production.