Determination of the archaeal and bacterial communities in two-phase and single-stage anaerobic systems by 454 pyrosequencing

2-Phase anaerobic digestion (AD), where the acidogenic phase was operated at 2 day hydraulic retention time (HRT) and the methanogenic phase at 10 days HRT, had been evaluated to determine if it could provide higher organic reduction and methane production than the conventional single-stage AD (also operated at 12 days HRT). 454 pyrosequencing was performed to determine and compare the microbial communities. The acidogenic reactor of the 2-phase system yielded a unique bacterial community of the lowest richness and diversity, while bacterial profiles of the methanogenic reactor closely followed the single-stage reactor. All reactors were predominated by hydrogenotrophic methanogens, mainly Methanolinea. Unusually, the acidogenic reactor contributed up to 24% of total methane production in the 2-phase system. This could be explained by the presence of Methanosarcina and Methanobrevibacter, and their activities could also help regulate reactor alkalinity during high loading conditions through carbon dioxide production. The enrichment of hydrolytic and acidogenic Porphyromonadaceae, Prevotellaceae, Ruminococcaceae and unclassified Bacteroidetes in the acidogenic reactor would have contributed to the improved sludge volatile solids degradation, and ultimately the overall 2-phase system''s performance. Syntrophic acetogenic microorganisms were absent in the acidogenic reactor but present in the downstream methanogenic reactor, indicating the retention of various metabolic pathways also found in a single-stage system. The determination of key microorganisms further expands our understanding of the complex biological functions in AD process.     

Uptake of radioiodide by Paenibacillus sp., Pseudomonas sp., Burkholderia sp. and Rhodococcus sp. isolated from a boreal nutrient-poor bog

Radionuclides, like radioiodine(~(129)I), may escape deep geological nuclear waste repositories and migrate to the surface ecosystems. In surface ecosystems, microorganisms can affect their movement. Iodide uptake of six bacterial strains belonging to the genera Paenibacillus,Pseudomonas, Burkholderia and Rhodococcus isolated from an acidic boreal nutrient-poor bog was tested. The tests were run in four different growth media at three temperatures. All bacterial strains removed iodide from the solution with the highest efficiency shown by one of the Paenibacillus strains with 99% of iodide removed from the solution in one of the used growth media. Pseudomonas, Rhodococcus and one of the two Paenibacillus strains showed highest iodide uptake in 1% yeast extract with maximum values for the distribution coefficient(K_d) ranging from 90 to 270 L/kg DW. The Burkholderia strain showed highest uptake in 1% Tryptone(maximum K_d170 L/kg DW). The Paenibacillus strain V0-1-LW showed exceptionally high uptake in 0.5% peptone + 0.25% yeast extract broth(maximum K_d 1,000,000 L/kg DW). Addition of 0.1% glucose to the 0.5% peptone + 0.25% yeast extract broth reduced iodide uptake at 4℃ and 20℃ and enhanced iodide uptake at 37℃ compared to the uptake without glucose. This indicates that the uptake of glucose and iodide may be competing processes in these bacteria. We estimated that in in situ conditions of the bog,the bacterial uptake of iodide accounts for approximately 0.1%–0.3% of the total sorption of iodide in the surface, subsurface peat, gyttja and clay layers.     

Microcystis aeruginosa/Pseudomonas pseudoalcaligenes interaction effects on off-flavors in algae/bacteria co-culture system under different temperatures

We conducted an experiment to study the interaction effects of Microcystis aeruginosa and Pseudomonas pseudoalcaligenes on off-flavors in an algae/bacteria co-culture system at three temperatures (24, 28 and 32°C). Gas chromatography–mass spectrometry was applied to measure off-flavor compounds dimethyl sulfide (DMS), dimethyl trisulfide (DMTS), 2-methylisoborneol, geosmin (GEO) and β-cyclocitral. During the lag phase of co-cultured M. aeruginosa (first 15 days), P. pseudoalcaligenes significantly increased the production of DMS, DMTS and β-cyclocitral at all three temperatures. In the exponential phase of co-cultured M. aeruginosa (after 15 days), M. aeruginosa became the main factor on off-flavors in the co-culture system, and β-cyclocitral turned to the highest off-flavor compound. These results also indicated that DMS, DMTS and β-cyclocitral were the main off-flavor compounds in our M. aeruginosa/P. pseudoalcaligenes co-culture system. Univariate analysis was applied to investigate the effects of M. aeruginosa and P. pseudoalcaligenes on the production of off-flavors. The results demonstrated that both M. aeruginosa and P. pseudoalcaligenes could increase the production of DMS and DMTS, while β-cyclocitral was mainly determined by M. aeruginosa. Our results also provide some insights into understanding the relationship between cyanobacteria and heterotrophic bacteria.     

Performance of low temperature Microbial Fuel Cells (MFCs) catalyzed by mixed bacterial consortia

Microbial Fuel Cells(MFCs) are a promising technology for treating wastewater in a sustainable manner. In potential applications, low temperatures substantially reduce MFC performance. To better understand the effect of temperature and particularly how bioanodes respond to changes in temperature, we investigated the current generation of mixed-culture and pure-culture MFCs at two low temperatures, 10°C and 5°C. The results implied that the mixed-culture MFC sustainably performed better than the pure-culture(Shewanella) MFC at 10°C, but the electrogenic activity of anodic bacteria was substantially reduced at the lower temperature of 5°C. At 10°C, the maximum output voltage generated with the mixed-culture was 540–560 m V, which was 10%–15% higher than that of Shewanella MFCs. The maximum power density reached 465.3 ± 5.8 m W/m~2 for the mixed-culture at10°C, while only 68.7 ± 3.7 m W/m~2 was achieved with the pure-culture. It was shown that the anodic biofilm of the mixed-culture MFC had a lower overpotential and resistance than the pure-culture MFC. Phylogenetic analysis disclosed the prevalence of Geobacter and Pseudomonas rather than Shewanella in the mixed-culture anodic biofilm, which mitigated the increase of resistance or overpotential at low temperatures.     

Comparative cytotoxicity of nanoparticles and ions to Escherichia coli in binary mixtures

The objective of this study was to understand toxicity of mixture of nanoparticles (NPs) (ZnO and TiO₂) and their ions to Escherichia coli. Results indicated the decrease in percentage growth of E. coli with the increase in concentration of NPs both in single and mixture setups. Even a small concentration of 1 mg/L was observed to be significantly toxic to E. coli in binary mixture setup (exposure concentration: 1 mg/L ZnO and 1 mg/L TiO₂; 21.15% decrease in plate count concentration with respect to control). Exposure of E. coli to mixture of NPs at 1000 mg/L (i.e., 1000 mg/L ZnO and 1000 mg/L TiO₂) resulted in 99.63% decrease in plate count concentration with respect to control. Toxic effects of ions to E. coli were found to be lesser than their corresponding NPs. The percentage growth reduction was found to be 36% for binary mixture of zinc and titanium ions at the highest concentration (i.e., 803.0 mg/L Zn and 593.3 mg/L Ti where ion concentrations are equal to the Zn ions present in 1000 mg/L ZnO NP solution and Ti^+ 4 ions present in 1000 mg/L TiO₂ NP solution). Nature of mixture toxicity of the two NPs to E. coli was found to be antagonistic. The alkaline phosphatase (Alp) assay indicated that the maximum damage was observed when E. coli was exposed to 1000 mg/L of mixture of NPs. This study tries to fill the knowledge gap on information of toxicity of mixture of NPs to bacteria which has not been reported earlier.     

Development of a field enhanced photocatalytic device for biocide of coliform bacteria

A field enhanced flow reactor using bias assisted photocatalysis was developed for bacterial disinfection in lab-synthesized and natural waters. The reactor provided complete inactivation of contaminated waters with flow rates of 50 m L/min. The device consisted of titanium dioxide nanotube arrays, with an externally applied bias of up to 6 V. Light intensity, applied voltage, background electrolytes and bacteria concentration were all found to impact the device performance. Complete inactivation of Escherichia coli W3110(~ 8 × 10~3CFU/m L) occurred in 15 sec in the reactor irradiated at 25 m W/cm~2 with an applied voltage of 4 V in a 100 ppm NaCl solution. Real world testing was conducted using source water from Emigration Creek in Salt Lake City, Utah. Disinfection of natural creek water proved more challenging, providing complete bacterial inactivation after 25 sec at 6 V. A reduction in bactericidal efficacy was attributed to the presence of inorganic and organic species, as well as the increase in robustness of natural bacteria.     

Metals and metalloid bioconcentrations in the tissues of Typha latifolia grown in the four interconnected ponds of a domestic landfill site

The uptake of metals in roots and their transfer to rhizomes and above-ground plant parts (stems, leaves) of cattails (Typha latifolia L.) were studied in leachates from a domestic landfill site (Etueffont, France) and treated in a natural lagooning system. Plant parts and corresponding water and sediment samples were taken at the inflow and outflow points of the four ponds at the beginning and at the end of the growing season. Concentrations of As, Cd, Cr, Cu, Fe, Mn, Ni and Zn in the different compartments were estimated and their removal efficiency assessed, reaching more than 90% for Fe, Mn and Ni in spring and fall as well in the water compartment. The above- and below-ground cattail biomass varied from 0.21 to 0.85, and 0.34 to 1.24 kg dry weight/m², respectively, the highest values being recorded in the fourth pond in spring 2011. The root system was the first site of accumulation before the rhizome, stem and leaves. The highest metal concentration was observed in roots from cattails growing at the inflow of the system''s first pond. The trend in the average trace element concentrations in the cattail plant organs can generally be expressed as: Fe > Mn > As > Zn > Cr > Cu > Ni > Cd for both spring and fall. While T. latifolia removes trace elements efficiently from landfill leachates, attention should also be paid to the negative effects of these elements on plant growth.     

Biodegradation of nicosulfuron by a novel Alcaligenes faecalis strain ZWS11

A bacterial strain ZWS11 was isolated from sulfonylurea herbicide-contaminated farmland soil and identified as a potential nicosulfuron-degrading bacterium. Based on morphological and physicochemical characterization of the bacterium and phylogenetic analysis of the 16S rRNA sequence, strain ZWS11 was identified as Alcaligenes faecalis. The effects of the initial concentration of nicosulfuron, inoculation volume, and medium pH on degradation of nicosulfuron were investigated. Strain ZWS11 could degrade 80.56% of the initial nicosulfuron supplemented at 500.0 mg/L under the conditions of pH 7.0, 180 r/min and 30°C after incubation for 6 days. Strain ZWS11 was also capable of degrading rimsulfuron, tribenuron-methyl and thifensulfuron-methyl. Four metabolites from biodegradation of nicosulfuron were identified, which were 2-aminosulfonyl-N, N-dimethylnicotinamide (M1), 4, 6-dihydroxypyrimidine (M2), 2-amino-4, 6-dimethoxypyrimidine (M3) and 2-(1-(4,6-dimethoxy-pyrimidin-2-yl)-ureido)-N,N-dimethyl-nicotinamide (M4). Among the metabolites detected, M2 was reported for the first time. Possible biodegradation pathways of nicosulfuron by strain ZWS11 were proposed. The degradation proceeded mainly via cleavage of the sulfonylurea bridge, O-dealkylation, and contraction of the sulfonylurea bridge by elimination of a sulfur dioxide group. The results provide valuable information for degradation of nicosulfuron in contaminated environments.     

Achieving partial nitrification by inhibiting the activity of Nitrospira-like bacteria under high-DO conditions in an intermittent aeration reactor

It is generally accepted that a low dissolved oxygen(DO) concentration is more beneficial for achieving partial nitrification than high-DO. In this study, partial nitrification was not established under low-DO conditions in an intermittent aeration reactor for treating domestic wastewater. During the operational period of low-DO conditions(DO: 0.3 ±0.14 mg/L), stable complete nitrification was observed. The abundance of Nitrospira-like bacteria, which were the major nitrite-oxidizing bacteria, increased from 1.03 × 10~6to2.64 × 10~6cells/m L. At the end of the low-DO period, the batch tests showed that high-DO concentration(1.5, 2.0 mg/L) could inhibit nitrite oxidation, and enhance ammonia oxidation. After switching to the high-DO period(1.8 ± 0.32 mg/L), partial nitrification was gradually achieved. Nitrospira decreased from 2.64 × 10~6 to 8.85 × 10~5cells/m L. It was found that suddenly switching to a high-DO condition could inhibit the activity and abundance of Nitrospira-like bacteria, resulting in partial nitrification.     

Chemical composition and properties of ashes from combustion plants using Miscanthus as fuel

Miscanthus giganteus is one of the energy crops considered to show potential for a substantial contribution to sustainable energy production. In the literature there is little data available about the chemical composition of ashes from the combustion of Miscanthus and practically no data about their physical properties. However, for handling, treatment and utilization of the ashes this information is important. In this study ashes from two biomass combustion plants using Miscanthus as fuel were investigated. The density of the ashes was 2230 ± 35 kg/m~3, which was similar to the density of ashes from straw combustion. Also the bulk densities were close to those reported for straw ashes. The flowability of the ashes was a little worse than the flowability of ashes from wood combustion. The measured heavy metal concentrations were below the usual limits for utilization of the ashes as soil conditioner. The concentrations in the bottom ash were similar to those reported for ash from forest residue combustion plants. In comparison with cyclone fly ashes from forest residue combustion the measured heavy metal concentrations in the cyclone fly ash were considerably lower. Cl-, S and Zn were enriched in the cyclone fly ash which is also known for ashes from wood combustion. In comparison with literature data obtained from Miscanthus plant material the concentrations of K, Cl-and S were lower.This can be attributed to the fact that the finest fly ash is not collected by the cyclone de-dusting system of the Miscanthus combustion plants.     

Biodegradation of indole by a newly isolated Cupriavidus sp. SHE

Indole, a typical nitrogen heterocyclic aromatic pollutant, is extensively spread in industrial wastewater. Microbial degradation has been proven to be a feasible approach to remove indole, whereas the microbial resources are fairly limited. A bacterial strain designated as SHE was isolated and found to be an efficient indole degrader. It was identified as Cupriavidus sp. according to 16S rRNA gene analysis. Strain SHE could utilize indole as the sole carbon source and almost completely degrade 100 mg/L of indole within 24 hr. It still harbored relatively high indole degradation capacity within pH 4–9 and temperature 25°C–35°C. Experiments also showed that some heavy metals such as Mn^2 +, Pb^2 + and Co^2 + did not pose severe inhibition on indole degradation. Based on high performance liquid chromatography–mass spectrum analysis, isatin was identified as a minor intermediate during the process of indole biodegradation. A major yellow product with m/z 265.0605 (C₁₅H₈N₂O₃) was generated and accumulated, suggesting a novel indole conversion pathway existed. Genome analysis of strain SHE indicated that there existed a rich set of oxidoreductases, which might be the key reason for the efficient degradation of indole. The robust degradation ability of strain SHE makes it a promising candidate for the treatment of indole containing wastewater.     

Examination of in vivo mutagenicity of sodium arsenite and dimethylarsinic acid in gpt delta rats

Arsenic is a well-known human bladder and liver carcinogen, but its exact mechanism of carcinogenicity is not fully understood. Dimethylarsinic acid(DMAV) is a major urinary metabolite of sodium arsenite(i As~Ⅲ) and induces urinary bladder cancers in rats. DMAVand i As~Ⅲare negative in in vitro mutagenicity tests. However, their in vivo mutagenicities have not been determined. The purpose of present study is to evaluate the in vivo mutagenicities of DMAVand i As~Ⅲin rat urinary bladder epithelium and liver using gpt delta F344 rats.Ten-week old male gpt delta F344 rats were randomized into 3 groups and administered 0,92 mg/L DMAV, or 87 mg/L i As~Ⅲ(each 50 mg/L As) for 13 weeks in the drinking water. In the mutation assay, point mutations are detected in the gpt gene by 6-thioguanine selection(gpt assay) and deletion mutations are identified in the red/gam genes by Spi-selection(Spi-assay). Results of the gpt and Spi-assays showed that DMAVand i As~Ⅲhad no effects on the mutant frequencies or mutation spectrum in urinary bladder epithelium or liver. These findings indicate that DMAVand i As~Ⅲare not mutagenic in urinary bladder epithelium or liver in rats.     

Effects of water regime,crop residues,and application rates on control of Fusarium oxysporum f. sp. cubense

Biological soil disinfestation is an effective method to control soil-borne disease by flooding and incorporating with organic amendments, but field conditions and resources sometimes limited its practical application. A laboratory experiment was conducted to develop practice guidelines on controlling Fusarium wilt, a widespread banana disease caused by Fusarium oxysporum f. sp. cubense (FOC). FOC infested soil incorporated with rice or maize straw at rates of 1.5 tons/ha and 3.0 tons/ha was incubated under flooded or water-saturated (100% water holding capacity) conditions at 30°C for 30 days. Results showed that FOC populations in the soils incorporated with either rice or maize straw rapidly reduced more than 90% in the first 15 days and then fluctuated till the end of incubation, while flooding alone without organic amendment reduced FOC populations slightly. The rapid and dramatic decrease of redox potential (down to − 350 mV) in straw-amended treatments implied that both anaerobic condition and strongly reductive soil condition would contribute to pathogen inactivation. Water-saturation combined with straw amendments had the comparable effects on reduction of FOC, indicating that flooding was not indispensable for inactivating FOC. There was no significant difference in the reduction of FOC observed in the straw amendments at between 1.5 and 3 tons/ha. Therefore, incorporating soil with straw (rice or maize straw) at a rate of 3.0 tons/ha under 100% water holding capacity or 1.5 tons/ha under flooding, would effectively alleviate banana Fusarium wilt caused by FOC after 15-day treating under 30°C.     

Biodegradation of pendimethalin by Bacillus subtilis Y3

A bacterium strain Y3,capable of efficiently degrading pendimethalin,was isolated from activated sludge and identified as Bacillus subtilis according to its phenotypic features and 16 S rRNA phylogenetic analysis.This strain could grow on pendimethalin as a sole carbon source and degrade 99.5%of 100 mg/L pendimethalin within 2.5 days in batch liquid culture,demonstrating a greater efficiency than any other reported strains.Three metabolic products,6-aminopendimethalin,5-amino-2-methyl-3-nitroso-4-(pentan-3-ylamino) benzoic acid,and 8-amino-2-ethyl-5-(hydroxymethyl)-1,2-dihydroquinoxaline-6-carboxylic acid,were identified by HPLC-MS/MS,and a new microbial degradation pathway was proposed.A nitroreductase catalyzing nitroreduction of pendimethalin to 6-aminopendimethalin was detected in the cell lysate of strain Y3.The cofactor was nicotinamide adenine dinucleotide phosphate(NADPH) or more preferably nicotinamide adenine dinucleotide(NADH).The optimal temperature and pH for the nitroreductase were 30℃ and 7.5,respectively.Hg~(2+),Ni~(2+),Pb~(2+),Co~(2+),Mn~(2+) Cu~(2+),Ag~+,and EDTA severely inhibited the nitroreductase activity,whereas Fe~(2+),Mg~(2+),and Ca~(2+) enhanced it.This study provides an efficient pendimethalin-degrading microorganism and broadens the knowledge of the microbial degradation pathway of pendimethalin.     

Sediment pollution characteristics and in situ control in a deep drinking water reservoir

Sediment pollution characteristics, in situ sediment release potential, and in situ inhibition of sediment release were investigated in a drinking water reservoir. Results showed that organic carbon (OC), total nitrogen (TN), and total phosphorus (TP) in sediments increased from the reservoir mouth to the main reservoir. Fraction analysis indicated that nitrogen in ion exchangeable form and NaOH-extractable P (Fe/Al-P) accounted for 43% and 26% of TN and TP in sediments of the main reservoir. The Risk Assessment Code for metal elements showed that Fe and Mn posed high to very high risk. The results of the in situ reactor experiment in the main reservoir showed the same trends as those observed in the natural state of the reservoir in 2011 and 2012; the maximum concentrations of total OC, TN, TP, Fe, and Mn reached 4.42 mg/L, 3.33 mg/L, 0.22 mg/L, 2.56 mg/L, and 0.61 mg/L, respectively. An in situ sediment release inhibition technology, the water-lifting aerator, was utilized in the reservoir. The results of operating the water-lifting aerator indicated that sediment release was successfully inhibited and that OC, TN, TP, Fe, and Mn in surface sediment could be reduced by 13.25%, 15.23%, 14.10%, 5.32%, and 3.94%, respectively.     

Effects of a municipal effluent on the freshwater mussel Elliptio complanata following challenge with Vibrio anguillarum

The purpose of this study was to examine the cumulative effects of exposure to a pathogenic bacteria and municipal effluent in the freshwater mussel Elliptio complanata. Mussels were exposed to increasing concentrations of an ozone-treated effluent at 15°C for 7 days. A sub-group of mussels was inoculated with Vibrio anguillarum and exposed to the same conditions as above.After the exposure period, mussels were collected to assess hemocyte count and viability,immunocompetence(phagocytosis and nitrite production), oxidative stress/inflammation(cyclooxygenase and lipid peroxidation) and oxygen radical/xenobiotic scavenging activity(metallothioniens, glutathione S-transferase). The results showed that mussels exposed to municipal effluent had increased hemocyte counts, phagocytosis, nitrites, lipid peroxidation and metallothioneins. In the inoculated mussels, the same responses were observed, in addition to cyclooxygenase and glutathione S-transferase activities. Multivariate analyses revealed that(1)the response pattern changed with effluent concentration, where increased responses observed at low effluent concentrations(10%, V/V) were attenuated at higher effluent concentrations,(2)the effluent produced more pronounced changes in lipid peroxidation, metallothionein and hemocyte viability, and(3) the simultaneous presence of V. anguillarum led to more important changes in hemocyte count and viability and nitrite levels. In conclusion, the presence of V.anguillarum could alter the response of mussels to municipal effluent, which could lead to increased inflammation in mussels.     

Effects of silver adsorbed on fumed silica, silver phosphate glass, bentonite organomodified with silver and titanium dioxide in aquatic indicator organisms

In order to reduce the level of transmission of diseases caused by bacteria and fungi, the development of antimicrobial additives for use in personal care, hygiene products, clothing and others has increased. Many of these additives are based on metals such as silver and titanium. The disposal of these products in the environment has raised concerns pertaining to their potential harmfulness for beneficial organisms. The objective of this study was to evaluate the influence of the shape, surface chemistry, size and carrier of three additives containing silver and one with titanium dioxide (TiO₂) on microcrustacean survival. Daphnia magna was used as a bioindicator for acute exposure test in suspensions from 0.0001 to 10,000 ppm. Ceriodaphnia dubia was used for chronic test in TiO₂ suspensions from 0.001 to 100 ppm. D. magna populations presented high susceptibility to all silver based additives, with 100% mortality after 24 hr of exposure. A different result was found in the acute experiments containing TiO₂ suspensions, with mortality rates only after 48 hr of incubation. Even on acute and chronic tests, TiO₂ did not reach a linear concentration-response versus mortality, with 1 ppm being more toxic than 10,000 ppm on acute test and 0.001 more toxic than 0.01 ppm on chronic assay. Silver based material toxicity was attributed to silver itself, and had no relation to either form (nano or ion) or carrier (silica, phosphate glass or bentonite). TiO₂ demonstrated to have a low acute toxicity against D. magna.     

Metal release/accumulation during the decomposition of Potamogeton crispus in a shallow macrophytic lake

Changes in metal concentrations in the litter of Potamogeton crispus were monitored during a consecutive 40-day in situ decomposition experiment using the litterbag method.The accumulation index was calculated and used to indicate the changes in the metals in litter.The results showed that the concentrations of Al,Cd,Cr,Fe,Mn,and Pb in litter increased significantly during the decomposition,while Cu and Zn concentrations decreased dramatically.Significant positive correlations were found between the concentrations of Al,Cr,Fe,and Mn and between Cu and Zn.Moreover,Cu and Zn both negatively correlated with Al and Fe.The remaining dry mass was negatively correlated with Al and Fe concentrations but positively correlated with Cu and Zn concentrations.Generally the accumulation index values of metals other than Al were less than one,indicating that the litter of P.crispus acted as a source of metals to the surrounding water body.Al was the only metal that showed continuous net accumulation in litter.The net accumulation of Fe and Mn in litter during the last 10 days of the experiment may indicate the precipitation of Feand Mn-oxides.It was estimated that 160 g/m~2(dry weight)P.crispus was decomposed in40 days.This was equivalent to releasing the following amounts of metals:0.01 mg Cd,0.03 mg Cr,0.71 mg Cu,0.55 mg Mn,0.02 mg Pb and 13.8 mg Zn into surrounding water,and accumulating 149 mg Al and 11 mg Fe,in a 1 m~2 area.     

Fe2+、Co2+、Ni2+对渗滤液厌氧过程的影响

通过单因素和正交试验,分别研究了Fe2+、Co2+、Ni2+及其组合对渗滤液厌氧过程中COD去除率和产甲烷量的影响.结果表明,分别投加Fe2+=25 mg·L-1、Co2+=1 mg·L-1、Ni2+=0.5 mg·L-1时对COD去除率和产甲烷量促进显著,3种微量元素均表现出了"低促高抑"的Hormesis效应.微量元素组合投加时,协同促进了甲烷的产生,其中Co2+是影响COD去除率的主要因素,Fe2+是影响产甲烷量的主要因素,但3种微量元素在其各自适宜的投加浓度范围时,对渗滤液厌氧过程的促进效果较为相近.各试验组的pH值维持在7.05~7.53之间,并与产甲烷量呈显著的相关关系.此外,渗滤液成分复杂,微量元素的生物有效性一定程度上受到限制,渗滤液厌氧体系对微量元素的需求较别的体系偏高.     

Arsenic methylation by an arsenite S-adenosylmethionine methyltransferase from Spirulina platensis

Arsenic-contaminated water is a serious hazard for human health. Plankton plays a critical role in the fate and toxicity of arsenic in water by accumulation and biotransformation.Spirulina platensis(S. platensis), a typical plankton, is often used as a supplement or feed for pharmacy and aquiculture, and may introduce arsenic into the food chain, resulting in a risk to human health. However, there are few studies about how S. platensis biotransforms arsenic. In this study, we investigated arsenic biotransformation by S. platensis. When exposed to arsenite(As(Ⅲ)), S. platensis accumulated arsenic up to 4.1 mg/kg dry weight.After exposure to As(Ⅲ), arsenate(As(Ⅴ)) was the predominant species making up 64% to86% of the total arsenic. Monomethylarsenate(MMA(Ⅴ)) and dimethylarsenate(DMA(Ⅴ))were also detected. An arsenite S-adenosylmethionine methyltransferase from S. platensis(Sp Ars M) was identified and characterized. Sp Ars M showed low identity with other reported Ars M enzymes. The Escherichia coli AW3110 bearing Spars M gene resulted in As(Ⅲ) methylation and conferring resistance to As(Ⅲ). The in vitro assay showed that Sp Ars M exhibited As(Ⅲ) methylation activity. DMA(Ⅴ) and a small amount of MMA(Ⅴ) were detected in the reaction system within 0.5 hr. A truncated Sp Ars M derivative lacking the last 34 residues still had the ability to methylate As(Ⅲ). The three single mutants of Sp Ars M(C59S, C186 S, and C238S) abolished the capability of As(Ⅲ) methylation, suggesting the three cysteine residues are involved in catalysis. We propose that Sp Ars M is responsible for As methylation and detoxification of As(Ⅲ) and may contribute to As biogeochemistry.