Dissimilatory reduction of perchlorate and other common pollutants by a consortium enriched from tidal flats of the Yellow Sea

Objective:To enrich a facultative anaerobic bacterial consortium from the Yellow Sea and assess its ability to reduce perchlorate and other co-pollutants.Methods:Bacterial consortium collected from the tidal flats of the Yellow Sea was enriched in an anoxic medium containing perchlorate as the electron(e^(-))acceptor and acetate as the electron(e^(-))donor.The enriched consortium was then tested for perchlorate reduction under different perchlorate concentrations and in the presence of nitrate by using standard anaerobic techniques.The complete enzymatic reduction of perchlorate to chloride was confirmed by chlorite dismutation.Ability of the consortium to grow with alternate e^(-)acceptors was also tested with acetate as the e^(-)donor.Results:The enriched consortium could rapidly reduce perchlorate up to the initial concentration of 25.65 mmol/L.In the presence of nitrate,perchlorate reduction did not occur immediately and reduction of nitrate started after a lag phase,with concomitant accumulation of nitrite.The perchlorate^(-)enriched consortium could reduce chlorate,oxygen,Cr(VI),and selenate as the alternate e^(-)acceptors but failed to utilize sulfate,thiosulfate,sulfite,and nitrite.Conclusions:The consortium from the tidal flats of the Yellow Sea could reduce perchlorate and co-contaminants such as chlorate,nitrate,Cr(VI),and selenate under heterotrophic conditions with acetate as the e^(-)donor and carbon source.While perchlorate was completely dismutated into innocuous chloride and oxygen,accumulation of nitrite occurred during the reduction of nitrate.

Dissimilatory Fe(Ⅲ) reduction characteristics of paddy soil extract cultures treated with glucose or fatty acids

Dissimilatory Fe(Ⅲ) reduction is a universal process with irreplaceable biological and environmental importance in anoxic environments. Our knowledge about Fe(Ⅲ) reduction predominantly comes from pure cultures of dissimilatory Fe(Ⅲ) reducing bacteria (DFRB). The objective of this study was to compare the effects of glucose and a selection of short organic acids (citrate, succinate, pyruvate, propionate, acetate, and formate) on Fe(Ⅲ) reduction via the anaerobic culture of three paddy soil solutions with Fe...

Reduction of Nitrate to Ammonium in Selected Paddy Soils of China *1

Three paddy soils were examined for their capacities of dissimilatory reduction of nitrate to ammonium (DRNA). 15 N labelled KNO 3 was added at the rate of 100 mg N kg -1 . Either glucose or rice straw powder was incorporated at the rate of 1.0 or 2.0 mg C kg -1 respectively. Three treatments were designed to keep the soil saturated with water: A) a 2 cm water layer on soil surface (with beaker mouth open); B) a 2 cm water layer and a 1 cm liquid paraffin layer (with beaker mouth open); and C) water saturated under O 2 free Ar atmosphere. The soils were incubated at 28 oC for 5 days. There was almost no 15 N labelled NH + 4 N detected in Treatment A. However, there was 1.4 to 3.4 mg N kg -1 15 N labelled NH + 4 N in Treatment B and 2.1 to 13.8 mg N kg -1 in Treatment C. Glucose was more effective than straw powder in ammonium production. Because there was sufficient amount of non labelled NH + 4 N in the original soils, 15 N labelled NH + 4 N produced as such should be the result of dissimilatory reduction. Studies on microbial population showed that there were plenty of bacteria responsible for DRNA process (DRNA bacteria) in the soils examined, indicating that number of DRNA bacteria was not a limiting factor for ammonium production. However, DRNA bacteria were inferior in number to denitrifiers. DRNA process in soil suspension seemed to start after 5 days of incubation. Glycerol and sodium succinate, though both are readily available carbon sources to organisms,did not facilitate DRNA process. DRNA occurred only when glucose was available and at the C/NO 3 - N ratio of over 12. It seemed that both availability and quality of the carbon sources affected DRNA.

Denitrification and Nitrate Reduction to Ammoniumin Taihu Lake and Yellow Sea Inter-Tidal MarineSediments

Denitrification and nitrate reduction to ammonium in Taihu Lake and Yellow Sea inter-tidal marinesediments were studied. The sediment samples were made into slurry containing 150 g dry matter per liter.Various amounts of glucose and 5 mmol L-1 of potassium nitrate were added in order to achieve differentratios of glucose-C to nitrate-N. Acetylene inhibition technique was applied to measure denitrification in theslumes. All samples were incubated anaerobically under argon atmosphere. Data showed that Taihu Lakesediment produced more N2O than marine sediment. Denitrification potential was higher in Taihu Lakesediment than in marne one. Glucose added increased denitrification activity but not the denitrification po-tential of the sediments. Dissimilatory nitrate reduction to ammonium seemed to occur in marine sediment,but not in freshwater one. When the marine sediment was treated with 25 mmol L-1 glucose, its denitrification poteatial, as indicated by maximum N2O production by acetylene blockage, was lower than that treatedwith no or 2.5 mmol L-l glucose. Acetylene was suspected to have inhibitory effect on dissimilatory nitratereduction to ammonium.

Nitrous Oxide and Methane Emissions as Affected by Water,Soil and Nitrogen

Specific management of water regimes, soil and N in China might play an important role in regulating N2O and CH4 emissions in rice fields. Nitrous oxide and methane emissions from alternate non-flooded/flooded paddies were monitored simultaneously during a 516-day incubation with lysimeter experiments. Two N sources (15N-(NH4)2SO4 and 15N-labeled milk vetch) were applied to two contrasting paddies: one derived from Xiashu loess (Loess) and one from Quaternary red clay (Clay). Both N2O and CH4 emissions were significantly higher in soil Clay than in soil Loess during the flooded period. For both soil, N2O emissions peaked at the transition periods shortly after the beginning of the flooded and non-flooded seasons. Soil type affected N2O emission patterns. In soil Clay, the emission peak during the transition period from non-flooded to flooded conditions was much higher than the peak during the transition period from flooded to non-flooded conditions. In soil Loess, the emission peak during the transition period from flooded to non-flooded conditions was obviously higher than the peak during the transition period from non-flooded to flooded conditions except for milk vetch treatment. Soil type also had a significant effect on CH4 emissions during the flooded season, over which the weighted average flux was 111 mg C m-2 h-1 and 2.2 mg C m-2 h-1 from Clay and Loess, respectively. Results indicated that it was the transition in the water regime that dominated N2O emissions while it was the soil type that dominated CH4 emissions during the flooded season. Anaerobic oxidation of methane possibly existed in soil Loess during the flooded season.

Effects of cathode potentials and nitrate concentrations on dissimilatory nitrate reductions by Pseudomonas alcaliphila in bioelectrochemical systems

The effects of cathode potentials and initial nitrate concentrations on nitrate reduction in bio- electrochemical systems （BESs） were reported. These factors could partition nitrate reduction between denitrification and dissimilatory nitrate reduction to ammonium （DNRA）. Pseudomonas alcaliphilastrain MBR utilized an electrode as the sole electron donor and nitrate as the sole electron acceptor. When the cathode potential was set from -0.3 to -I.1 V （vs. Ag/AgC1） at an initial nitrate concentration of 100 mg NO^-N/L, the DNRA electron recovery increased from （10.76 ± 1.6）% to （35.06 ± 0.99）%; the denitrification electron recovery decreased from （63.42 ± 1,32）% to （44.33 ± 1.92）%. When the initial nitrate concentration increased from （29.09 ± 0.24） to （490.97 ± 3.49） mg NO3-N/L at the same potential （-0.9 V）, denitrification electron recovery increased from （5.88 ± 1.08）% to （50.19 ±2.59）%; the DNRA electron recovery declined from （48.79 ±1.32）% to （16.02 ± 1.41）%. The prevalence of DNRA occurred at high ratios of electron donors to acceptors in the BESs and denitrification prevailed against DNRA under a lower ratio of electron donors to acceptors. These results had a potential application value of regulating the transformation of nitrate to N2 or ammonium in BESs for nitrate removal.

Dissimilatory iron reduction contributes to anaerobic mineralization of sediment in a shallow transboundary lake

Dissimilatory iron reduction(DIR)coupled with carbon cycling is increasingly being recognized as an influential process in freshwater wetland soils and sediments.The role of DIR in organic matter(OM)mineralization,however,is still largely unknown in lake sediment environments.In this study,we clarified rates and pathways of OM mineralization in two shallow lakes with seasonal hydrological connectivity and different eutrophic situations.We found that in comparison with the domination of DIR(55%)for OM mineralization in Lake Xiaoxingkai,the contribution of methanogenesis was much higher(68%)in its connected lake(Lake Xingkai).The differences in rates and pathways of sediment OM mineralization between the two lakes were attributed to higher concentrations of carbonate associated iron oxides(Fecarb)in Lake Xiaoxingkai compared to Lake Xingkai(P=0.002),due to better deposition mixing,more contributions of terrigenous detrital materials,and higher OM content in Lake Xiaoxingkai.Results of structural equation modeling showed that Fecarb and total iron content(TFe)regulated 25%of DIR in Lake Xiaoxingkai and 76%in Lake Xingkai,accompanied by a negative effect of TFe on methanogenesis in Lake Xingkai.The relative abundance and diversity of Fe-reducing bacteria were significantly different between the two lakes,and showed a weak effect on sediment OM mineralization.Our findings emphasize the role of iron minerals and geochemical characterizations in regulating rates and pathways of OM mineralization,and deepen the understanding of carbon cycling in lake sediments.

Marine aquaculture regulates dissimilatory nitrate reduction processes in a typical semi-enclosed bay of southeastern China

Marine aquaculture in semi-enclosed bays can significantly influence nutrient cycling in coastal ecosystems.However,the impact of marine aquaculture on the dynamics of dissimilatory nitrate reduction processes(DNRPs)and the fate of reactive nitrogen remain poorly understood.In this study,the rates of DNRPs and the abundances of related functional genes were investigated in aquaculture and non-aquaculture areas.The results showed that marine aquaculture significantly increased the denitrification(DNF)and dissimilatory nitrate reduction to ammonium(DNRA)rates and decreased the rate of anaerobic ammonium oxidation(ANA),as compared with non-aquaculture sites.DNF was the dominant pathway contributing to the total nitrate reduction,and its contribution to the total nitrate reduction significantly increased from 66.72%at non-aquaculture sites to 78.50%at aquaculture sites.Marine aquaculture can significantly affect the physicochemical characteristics of sediment and the abundances of related functional genes,leading to variations in the nitrate reduction rates.Although nitrate removal rates increased in the marine aquaculture area,ammonification rates and the nitrogen retention index in the aquaculture areas were 2.19 and 1.24 times,respectively,higher than those at non-aquaculture sites.Net reactive nitrogen retention exceeded nitrogen removal in the aquaculture area,and the retained reactive nitrogen could diffuse with the tidal current to the entire bay,thereby aggravating N pollution in the entire study area.These results show that marine aquaculture is the dominant source of nitrogen pollution in semi-enclosed bays.This study can provide insights into nitrogen pollution control in semi-enclosed bays with well-developed marine aquaculture.

Diverse transformations of sulfur in seabird-affected sediments revealed by microbial and stable isotope analyses

Microbial communities,sulfur isotope of sulfides(δ^(34)S_(AVS)and δ^(34)S_(CRS)),and sulfur and oxygen isotopes of sulfate(δ^(34)S_(SO_(4))and δ^(18)O_(SO_(4)))in sediments were analyzed to reveal the biogeochemical transformations of sulfur in a seabird-affected lake Y2 and a se abird-free YO from Fildes Peninsula,Antarctic Peninsula.The microbial communities in Y2 were mainly associated with penguin activities,while those in YO were limited by nutrients.The much enriched δ^(34)S_(SO_(4))recorded at depth of 30,41,and 52 cm in Y2indicates very strong sulfate reduction therein.The sulfur-degrading bacteria Pseudomonas in 0-23 cm of Y2 was 3.5 time s as abundant as that of sulfur oxidizing bacteria(SOB),indicating remarkable remineralization of organic sulfur.The abundant SOB and ^(34)S-depleted sulfate indicate considerable sulfur oxidation in 34-56-cm layer in Y2.In YO sediments,the highest abundance of Desulfotalea and the most enriched δ^(34)S_(SO_(4))(35.2‰)and δ^(34)S_(CRS)(2.5‰)indicate the strongest sulfate reduction in 28-cm layer.High abundance of Pseudomonas indicates active remineralization of organic sulfur in 3-5-cm layer in YO.The medium δ^(34)S_(SO_(4))and considerable abundance of SOB and sulfate-reducing bacteria(SRB)indicate concurrence of sulfur oxidation and sulfate reduction in other layers in YO.Therefore,a high level of organic matter input from penguin populations supported the diverse microbial community and transformations of sulfur in aquatic ecosystems in Antarctica.

Unveiling the mechanisms of Fe(Ⅲ)-loaded chitosan composite(CTS-Fe)in enhancing anaerobic digestion of waste activated sludge

Anaerobic digestion(AD)of waste activated sludge(WAS)is usually limited by the low generation efficiency of methane.Fe(Ⅲ)-loaded chitosan composite(CTS-Fe)have been reported to effectively enhanced the digestion of WAS,but its role in promoting anaerobic sludge digestion remains unclear.In present study,the effects of CTS-Fe on the hydrolysis and methanogenesis stages of WAS anaerobic digestion were investigated.The addition of CTSFe increased methane production potential by 8%-23%under the tested conditions with the addition of 5-20 g/L CTS-Fe.Besides,the results demonstrate that the addition of CTS-Fe could effectively promote the hydrolysis of WAS,evidenced by lower protein or polysaccharides concentration,higher soluble organic carbon in rector adding CTS-Fe,as well as the increased activity of extracellular hydrolase with higher CTS-Fe concentration.Meanwhile,the enrichment of Clostridia abundance(iron-reducing bacteria(IRBs))was observed in CTS-Fe adding reactor(8.9%-13.8%),which was higher than that in the control reactor(7.9%).The observation further suggesting the acceleration of hydrolysis through dissimilatory iron reduction(DIR)process,thus providing abundant substrates for methanogenesis.However,the presence of CTS-Fe was inhibited the acetoclastic and hydrogenotrophic methanogenesis process,which could be ascribed to the Fe(Ⅲ)act as electron acceptor coupled to methane for anaerobic oxidation.Furthermore,coenzyme F420 activity in the CTS-Fe added reactor was 34.9% lower than in the blank,also abundance of microorganisms involved in hydrogenotrophic methanogenesis was decreased.Results from this study could provide theoretical support for the practical applications of CTS-Fe.

Overlooked nitrogen-cycling microorganisms in biological wastewater treatment

Nitrogen-cycling microorganisms play key roles at the intersection of microbiology and wastewater engineering.In addition to the well-studied ammonia oxidizing bacteria,nitrite oxidizing bacteria,heterotrophic denitrifiers,and anammox bacteria,there are some other N-cycling microorganisms that are less abundant but functionally important in wastewater nitrogen removal.These microbes include,but not limited to ammonia oxidizing archaea(AOA),complete ammonia oxidation(comammox)bacteria,dissimilatory nitrate reduction to ammonia(DNRA)bacteria,and nitrate/nitrite-dependent anaerobic methane oxidizing(NO_(x)-DAMO)microorganisms.In the past decade,the development of high-throughput molecular technologies has enabled the detection,quantification,and characterization of these minor populations.The aim of this review is therefore to synthesize the current knowledge on the distribution,ecological niche,and kinetic properties of these“overlooked”N-cycling microbes at wastewater treatment plants.Their potential applications in novel wastewater nitrogen removal processes are also discussed.A comprehensive understanding of these overlooked N-cycling microbes from microbiology,ecology,and engineering perspectives will facilitate the design and operation of more efficient and sustainable biological nitrogen removal processes.

Mesoproterozoic biomineralization:Cyanobacterium-like filamentous siderite sheaths~1.4 Ga

Biomineralization was a key development in a wide variety of organisms,yet its history prior to the Ediacaran remains poorly understood.In this paper,we describe~1420-1330 million year old microscopic tubes preserved as siderite(FeCO_(3)).In size and shape these tubes closely resemble cyanobacterial sheaths forming mineralized mats.We consider two competing explanations for their formation.First,the tubes and associated sediment were originally composed of Ca-carbonate that was subsequently replaced by siderite.In this case,siderite mineralization was early,but post-mortem,as in early silicification,and preferentially preserved the more resilient sheath.However,no relict calcite is observed.Second,the Fe-carbonate mineralogy of the tubes and sediment is synsedimentary.In this case,photosynthetic oxygen may have precipitated Fe-oxyhydroxide that was promptly converted to siderite by dissimilatory iron reduction(DIR).Primary siderite mineralization of cyanobacteria has not been described before.Both explanations link photosynthetic processes to preferential sheath mineralization during the life of the cyanobacteria,as observed in present-day calcified cyanobacteria.This process might include CO_(2)-concentrating mechanisms(CCMs)linked to relatively low levels of atmospheric CO_(2),consistent with empirical estimates of mid-Proterozoic CO_(2)levels based on paleosols and weathering rinds.In either case,these cyanobacterium-like fossils preserved in siderite provide an early example of biomineralization and suggest the interactive in-fluences of both metabolic processes and ambient seawater chemistry.