典型草地土壤好氧甲烷氧化的微生物生态过程

【目的】针对我国甘肃三个典型生态区草地土壤(玛曲MQ、临泽LZ和环县HX),研究其甲烷氧化潜力、甲烷氧化菌(methane-oxidizingbacteria,MOB)丰度及可能存在的群落分异规律。【方法】通过原位分析、室内高浓度甲烷模拟培养三种典型土壤及实时荧光定量、高通量测序的方法研究甲烷氧化菌标靶基因pmoA序列的组成及其丰度变化规律。【结果】三种典型草地土壤的原位甲烷氧化菌的丰度存在显著差异,表现为MQ>HX>LZ,其数量范围为为0.18–6.86×10^7g/d.w.s.;甲烷氧化潜力也表现出类似规律,其通量为109–169mg/(m^2·h);甲烷氧化潜力与原位土壤中甲烷氧化菌丰度有正相关。三种草地土壤甲烷氧化菌存在明显的空间异质性,采用高通量测序的方法,发现三种草地原位土壤中的优势类群为USCγ(Upland Soil Cluster gamma,USCγ);然而,室内高浓度甲烷氧化过程中,传统的甲烷氧化菌均发生明显增加,MQ土壤中TypeⅡ的Methylocystis为优势类群,而LZ和HX土壤的优势类群均为TypeⅠ型Methylosarcina。【结论】这些研究结果表明,我国甘肃典型草地土壤中也存在难培养的大气甲烷氧化菌和经典的可培养甲烷氧化菌,这些微生物极可能氧化极低浓度的大气甲烷,也可能利用闭蓄于土壤中的高浓度甲烷生长。未来应采用先进技术原位观测大气甲烷氧化过程并分离相应微生物类群,研究草地土壤甲烷氧化菌地理分异规律及其环境驱动机制。     

Characterization of methanotrophic bacterial populations in soils showing atmospheric methane uptake.

The global methane cycle includes both terrestrial and atmospheric processes and may contribute to feedback regulation of the climate. Most oxic soils are a net sink for methane, and these soils consume approximately 20 to 60 Tg of methane per year. The soil sink for atmospheric methane is microbially mediated and sensitive to disturbance. A decrease in the capacity of this sink may have contributed to the approximately 1%. year(-1) increase in the atmospheric methane level in this century. The organisms responsible for methane uptake by soils (the atmospheric methane sink) are not known, and factors that influence the activity of these organisms are poorly understood. In this study the soil methane-oxidizing population was characterized by both labelling soil microbiota with (14)CH(4) and analyzing a total soil monooxygenase gene library. Comparative analyses of [(14)C]phospholipid ester-linked fatty acid profiles performed with representative methane-oxidizing bacteria revealed that the soil sink for atmospheric methane consists of an unknown group of methanotrophic bacteria that exhibit some similarity to type II methanotrophs. An analysis of monooxygenase gene libraries from the same soil samples indicated that an unknown group of bacteria belonging to the alpha subclass of the class Proteobacteria was present; these organisms were only distantly related to extant methane-oxidizing strains. Studies on factors that affect the activity, population dynamics, and contribution to global methane flux of "atmospheric methane oxidizers" should be greatly facilitated by use of biomarkers identified in this study.     

Responses of atmospheric methane consumption by soils to global climate change

Soils consume about 40 Tg methane from the atmosphere annually. Thus, soils contribute significantly to the atmospheric methane budget. However, responses of atmospheric methane consumption to climate change are uncertain. Predicting these responses requires an understanding of the effect on methane consumption of specific variables (temperature and soil water content) as well as interactions among parameters (methane, ammonium, water content). Key considerations involve the limitations of diffusive transport and controls of methane diffusivity; limitation of methanotrophic activity by water stress; relatively slow growth rates of methane-oxidizing bacteria on atmospheric methane; ammonium toxicity. Interactions among these parameters may be particularly important, and lead to responses contrary to those predicted from changes in temperature and water content alone. Results from a number of analyses indicate that atmospheric methane consumption is especially sensitive to anthropogenic disturbances, which typically decrease activity. Continued increases in wet and dry ammonium deposition are likely to exacerbate inhibition resulting from changes in land use. Changes in hydrological regimes could further decrease activity if dry periods increase water stress at soil depths currently colonized by methanotrophs. Future trends in the soil methane sink are likely to lead to enhanced accumulation of atmospheric methane.     

Routine fluorescence in situ hybridization in soil

The use of fluorescence in situ hybridization (FISH) to identify and enumerate soil bacteria has long been hampered by the autofluorescence of soil particles masking the bacterial signals and because the need of counting hundreds of bacteria in order to achieve statistically reliable data is time consuming. Recently, it was demonstrated that Nycodenz facilitates FISH in soil by concentrating bacteria on membrane filters and avoiding autofluorescent soil particles. We present a routine protocol for FISH in soil including the use of Nycodenz. The protocol allows fast and easy enumeration of hundreds of bacteria. We propose the use of silicon grease coated slides to treat in parallel seven samples per hybridization. Further, we developed a semi-automated approach for the enumeration of bacteria by implementing macros concatenating all steps of the image analyzes in the Image J software. Using Nycodenz, software-assisted bacterial counts statistically matched eye-counts of the same images and it was possible to count 880 DAPI stained bacteria per ten images. Fifty-five percent of these bacteria were co-labelled with the FISH probe specific for the Domain Bacteria, in accordance with recent FISH studies of bacterial populations in bulk soil. With a soil slurry protocol used for comparison, soil particles impaired automatic counts of the bacteria and FISH analysis, and only 88 DAPI stained bacteria per ten images could be counted by eye. With the Nycodenz protocol, 5 mM Na(2)EDTA used as an extractant increased the number of bacteria observed by 49%. In contrast, Tween 20 (1% or 5%) had no significant effect and increased the variability between the samples. Overall, the proposed procedure allows to process a high number of samples and to achieve a time efficient FISH characterization of soil bacterial communities.     

甲烷氧化混合菌的保藏方法研究

【目的】甲烷氧化混合菌是自然界中吸收甲烷的关键微生物,在甲烷氧化混合菌的研究和应用中,首先要解决其长期稳定保藏的问题,保藏方法应能有效保持菌群结构和功能的完整性、稳定性。【方法】以从煤矿土壤富集得到的两种结构稳定的甲烷氧化混合菌为实验体系,研究对比了冷藏法、低温冷冻法、石蜡油冷冻法、甘油冷冻法4种保藏方法,考察保藏前后混合菌的生长状况、MMO活性、菌群结构等。【结果】保藏6个月后,除甘油冷冻法以外,经其它3种方法保藏的混合菌,都具有与保藏前相当的细胞密度、甲烷氧化能力、MMO酶活以及传代稳定性,且DGGE图谱显示保藏前后的菌群结构变化不大。【结论】这3种保藏方法都可以有效的保持甲烷氧化混合菌功能和菌群结构的稳定性。     

Separation of Non-filamentous Micro-organisms from Soil by Density Gradient Centrifugation in Percoll

Soil suspensions were homogenized, and desorbed non-filamentous micro-organisms were concentrated in a minimum volume of buffer by low speed centrifugation. The cells were separated from inanimate material by flotation at the interface between the buffer and a silica sol/polyvinyl pyrrolidone density gradient medium (Percoll). Cell suspensions were removed from the interface and fractionated according to density by high speed centrifugation on discriminating density gradients in Percoll.
Preliminary experiments indicated that most non-filamentous soil micro-organisms had densities in the range 1.081–1.123 g%sol;ml while Rhizobium isolated from crushed root nodules on Percoll was split into two bands of densities 1.081–1.110 and 1.041–1.073 g/ml. The lighter cells were the more pleomorphic.
The efficiency of extraction of cells from soil was governed by the extent of their desorption from inanimate particles. As rigorous desorption procedures damage cells, extraction efficiencies were low; 10–20% of cells counted microscopically in soil were recovered from density gradients. Electron microscopy of soil micro-organisms isolated by this method showed an unusual range of surface ornamentations on cell-like structures of bacterial dimensions.     

Evaluation of methods for extraction of bacteria from soil

Abstract Several methods for dispersion of soil were tested for possible use in procedures for extraction of bacteria. Physical cell damage on cells and efficiency in extraction of indigenous cells from soil, were investigated. Cell damage by the dispersion methods was investigated by measuring the physical cell integrity and viability of pure cultures of Escherichia coli and Bacillus subtilis , as well as soil bacteria extracted from soil, when dispersed in slurries of γ-sterilized soil. Separation of bacteria and soil particles on the basis of buoyant density was conducted with the nonionic density gradient medium Nycodenz. When slurries of γ-sterilized soil with added pure cultured cells were centrifuged (10000 × g ) over cushions of Nycodenz (1.3 g ml⁻¹), practically all the added cells were recovered in a layer on top of the cushion. This proves that a reversible attachment and cosedimentation is not an important phenomenon in this procedure. The efficiency of the different dispersion methods for the extraction of indigenous soil bacteria, was assessed after separation of dislodged and attached soil bacteria. This separation was done either on the basis of sedimentation rate by low speed centrifugation, or buoyant density by Nycodenz density gradient centrifugation. The physical dispersion by ultrasonic treatment and chemical dispersion by the use of a chelating agent together with a detergent, were inferior to physical dispersion either by Waring blender (for large volumes) or a rotating rubber pestle treatment (for smaller volumes). The physical dispersion did not appear to be destructive to the cells tested.     

Quantitative and qualitative comparison of density-based purification methods for detection of Cryptosporidium oocysts in turbid environmental matrices

Purification methods for Cryptosporidium oocysts are usually selected on the basis of recovery yield, but the amount of particulate debris in environmental matrices could limit efficiency of oocyst detection by microscopic examination or PCR detection. Previous studies have shown that the standard immunomagnetic separation (IMS) procedure would not be the most suitable method for oocyst purification from turbid matrices. We compared the capacity of Percoll-sucrose flotation and six other density-based purification methods to achieve selective separation of Cryptosporidium oocysts from particulate debris. Rate of oocyst recovery and particulate loading in the purified suspensions were chosen as comparison criteria for the different purification methods. In most earlier studies, the chemical treatments employed to obtain a purified oocyst suspension modify the surface properties of oocysts in spiked samples. Assuming this produces unrealistic conditions affecting the evaluation of purification methods, we performed the present study with native oocysts. Flotation and gradient procedures were tested with and without formaldehyde ethyl acetate (FEA) separation. FEA separation was found to be unsuitable. Filtration and Percoll gradient did not allow selective oocyst separation from debris. Among the purification methods suitable for routine microscopic examination, Percoll-sucrose flotation provided the best recovery rates. For automated enumeration systems or PCR detection, potassium bromide and especially Nycodenz gradients appeared to be the most suitable purification methods. Potassium bromide and Nycodenz gradients provided the best balance between oocyst recovery and particulate load.     

长期不同施肥下水稻土甲烷氧化能力及甲烷氧化菌多样性的变化

稻田内源甲烷的氧化是稻田甲烷减排的重要途径。而甲烷氧化菌是土壤中甲烷氧化的主要施动者,在长期不同施肥条件下,土壤微生物群落的演变是否影响到土壤甲烷氧化菌群落结构及其活性,进而影响到田土壤CH4向大气的实际排放强度还不清楚。为此,选择太湖地区一个长期肥料试验的稻田土壤为研究对象,分析长期不同肥料施用对土壤甲烷氧化能力的影响及其与土壤中甲烷氧化菌群落结构变化的可能关系。结果表明,长期不同的施肥措施下稻田土壤对甲烷的氧化能力产生了明显差异,伴随着土壤中甲烷氧化菌（MOBI和MOBII）的基因群落多样性的显著变化。长期单一施用氮肥为主的化肥显著降低了土壤对甲烷的氧化能力,同时显著降低了稻田土壤甲烷氧化菌的多样性和丰富度;不同施肥下甲烷氧化菌多样性的变化与土壤的甲烷氧化能力的变化趋势相一致。因此,研究显示长期不同施肥处理下甲烷氧化菌群落结构的改变可能是引起水稻土甲烷氧化能力变化的一个主要因素,有机无机配合施用可以明显降低稻田土壤甲烷的大气释放潜能。但长期不同施肥处理下甲烷氧化菌活性的变化还有待于进一步研究。     

CO2浓度增加对长白山森林土壤甲烷氧化影响

大气CO2浓度升高可能对森林土壤的甲烷(CH4)氧化速率产生影响.本文采用开顶箱技术,对连续6年高浓度CO2(500 μmol·mol-1)处理的长白山森林典型树种蒙古栎树下土壤CH4氧化速率进行研究,并利用CH4氧化菌的16S rRNA特异性引物以及CH4单加氧酶功能基因引物分析了土壤中CH4氧化菌的群落结构与数量.结果表明:CO2浓度增高后,生长季土壤甲烷氧化量与对照和裸地相比分别降低了4％和22％;基于16S rRNA特异性引物的DGGE分析表明,CO2浓度增高导致两类甲烷氧化菌的多样性指数降低;CO2浓度增高对土壤中Ⅰ类甲烷氧化菌数量无显著影响,而使土壤中Ⅱ类甲烷氧化菌数量显著减少,功能基因pmoA拷贝数与对照和裸地相比分别降低了15％和46％.CO2浓度增高导致森林土壤甲烷氧化菌数量与活性降低,土壤含水量的增加可能是导致这一现象的主要原因.     

Comparative analysis of methane-oxidizing archaea and sulfate-reducing bacteria in anoxic marine sediments

The oxidation of methane in anoxic marine sediments is thought to be mediated by a consortium of methane-consuming archaea and sulfate-reducing bacteria. In this study, we compared results of rRNA gene (rDNA) surveys and lipid analyses of archaea and bacteria associated with methane seep sediments from several different sites on the Californian continental margin. Two distinct archaeal lineages (ANME-1 and ANME-2), peripherally related to the order Methanosarcinales, were consistently associated with methane seep marine sediments. The same sediments contained abundant (13)C-depleted archaeal lipids, indicating that one or both of these archaeal groups are members of anaerobic methane-oxidizing consortia. (13)C-depleted lipids and the signature 16S rDNAs for these archaeal groups were absent in nearby control sediments. Concurrent surveys of bacterial rDNAs revealed a predominance of delta-proteobacteria, in particular, close relatives of Desulfosarcina variabilis. Biomarker analyses of the same sediments showed bacterial fatty acids with strong (13)C depletion that are likely products of these sulfate-reducing bacteria. Consistent with these observations, whole-cell fluorescent in situ hybridization revealed aggregations of ANME-2 archaea and sulfate-reducing Desulfosarcina and Desulfococcus species. Additionally, the presence of abundant (13)C-depleted ether lipids, presumed to be of bacterial origin but unrelated to ether lipids of members of the order Desulfosarcinales, suggests the participation of additional bacterial groups in the methane-oxidizing process. Although the Desulfosarcinales and ANME-2 consortia appear to participate in the anaerobic oxidation of methane in marine sediments, our data suggest that other bacteria and archaea are also involved in methane oxidation in these environments.     

青海湖3种类型高寒湿地甲烷氧化菌群落特征

【背景】甲烷氧化菌在维持湿地生态系统碳平衡方面发挥着重要作用,青海湖高寒湿地具有十分重要的生态地位,但目前有关该地区甲烷氧化菌的研究相对较少。【目的】探究不同类型高寒湿地土壤甲烷氧化菌的群落特征与驱动因素。【方法】以青海湖流域内的小泊湖沼泽湿地、鸟岛湖滨湿地、瓦颜山河源湿地为研究对象,通过高通量测序技术对土壤甲烷氧化菌进行检测。【结果】3种不同类型高寒湿地土壤甲烷氧化菌的优势菌门均为变形菌门(Proteobacteria)。鸟岛湖滨湿地与瓦颜山河源湿地的甲烷氧化菌α多样性存在显著差异(P<0.05),而小泊湖沼泽湿地与二者的甲烷氧化菌α多样性的差异不显著(P>0.05)。LEfSe分析表明,不同类型高寒湿地共存在40个差异菌群,尤以瓦颜山河源湿地差异菌群数量最多,从门到属水平均存在显著差异。冗余分析(redundancy analysis,RDA)表明,甲烷氧化菌菌群变化的主要驱动因子为土壤温度、土壤水分、电导率。【结论】整体而言,青海湖3种类型高寒湿地土壤理化性质及甲烷氧化菌群落多样性均存在差异,且部分菌群的相对丰度具有显著性差异(P<0.05)。     

Seasonal Study of Methane Oxidation in Lake Washington

The distribution of methane and methane-oxidizing bacteria in the water column of Lake Washington was determined monthly for 1 year. The methane profiles were relatively constant, with little stratification and low concentrations (0.05 to 0.5 μM). The number of methane-oxidizing bacteria detected by a filter-plating method was routinely <1/ml throughout the water column, and no incorporation or oxidation of methane was detected by radioisotopic labeling, even after methane was added. However, samples taken from the sediment-water interface contained as much as 3 μM methane and 50 CFU of methane-oxidizing bacteria per ml and showed significant rates of methane oxidation and incorporation. To define the region of maximum activity more precisely, vertical profiles of the sediment were examined. The concentration of methane increased with depth to a maximum of 150 to 325 μM at 2.5 cm, and significant rates of methane oxidation were found within the top 2.5 cm. The apparent K_ms for methane and oxygen were determined for samples from the top 1.0 cm of the sediment and found to be ca. 10 and 20 μM, respectively. Projected values for methane oxidation rates suggested that maximum methane oxidation occurred in the top 0.5 cm of the sediment.     

Comparative Analysis of Methane-Oxidizing Archaea and Sulfate-Reducing Bacteria in Anoxic Marine Sediments

The oxidation of methane in anoxic marine sediments is thought to be mediated by a consortium of methane-consuming archaea and sulfate-reducing bacteria. In this study, we compared results of rRNA gene (rDNA) surveys and lipid analyses of archaea and bacteria associated with methane seep sediments from several different sites on the Californian continental margin. Two distinct archaeal lineages (ANME-1 and ANME-2), peripherally related to the order Methanosarcinales, were consistently associated with methane seep marine sediments. The same sediments contained abundant ¹³C-depleted archaeal lipids, indicating that one or both of these archaeal groups are members of anaerobic methane-oxidizing consortia. ¹³C-depleted lipids and the signature 16S rDNAs for these archaeal groups were absent in nearby control sediments. Concurrent surveys of bacterial rDNAs revealed a predominance of δ-proteobacteria, in particular, close relatives of Desulfosarcina variabilis. Biomarker analyses of the same sediments showed bacterial fatty acids with strong ¹³C depletion that are likely products of these sulfate-reducing bacteria. Consistent with these observations, whole-cell fluorescent in situ hybridization revealed aggregations of ANME-2 archaea and sulfate-reducing Desulfosarcina and Desulfococcus species. Additionally, the presence of abundant ¹³C-depleted ether lipids, presumed to be of bacterial origin but unrelated to ether lipids of members of the order Desulfosarcinales, suggests the participation of additional bacterial groups in the methane-oxidizing process. Although the Desulfosarcinales and ANME-2 consortia appear to participate in the anaerobic oxidation of methane in marine sediments, our data suggest that other bacteria and archaea are also involved in methane oxidation in these environments.     

Physicochemical and biological factors affecting atmospheric methane oxidation in gray forest soils

The decline of methane oxidizing activities in gray forest soil upon its conversion into arable land was shown to be caused by major changes in biotic and physicochemical properties of soil. Using the method of immune serums, methane-oxidizing bacteria were detected in both forest and agricultural soils, but their populations differed significantly in both abundance and composition. In the forest soil, the number of methanotrophs was an order of magnitude higher than in arable soil, amounting to 3.5 × 10⁸ and 0.24 × 10⁸ cells/g soil, respectively. All methane-oxidizing bacteria identified in the forest soil belonged to the genus Methylocystis, and 94% of these were represented by a single species, M. parvus. The arable soil was dominated by type I methanotrophs (Methylobacter and Methylomonas, 67.6%), occurring along with bacteria of the genus Methylocystis. In addition, arable soil is characterized by a low content of microbial biomass, lower porosity and water resistance of soil aggregates, and the predominance of nitrogen mineralization processes over those of nitrogen immobilization. These factors can also contribute to lower rates of methane oxidation in arable soil as compared to forest soil.__________Translated from Mikrobiologiya, Vol. 74, No. 2, 2005, pp. 255–260.Original Russian Text Copyright © 2005 by Kravchenko, Semenov, Kuznetsova, Bykova, Dulov, Pardini, Gispert, Boeckx, Cleemput, Galchenko.     

Biphasic kinetics of a methanotrophic community is a combination of growth and increased activity per cell

Because methane-oxidizing bacteria (MOB) are the only biological sink for the greenhouse gas methane, knowledge of the functioning of these bacteria in various ecosystems is needed to understand the dynamics observed in global methane emission. The activity of MOB is commonly assessed by methane oxidation assays. The resulting methane depletion curves often follow a biphasic pattern of initial and induced methane oxidation activity, often interpreted as representing the in situ active and total MOB community, respectively. The application of quantitative-PCR on soil incubations, which were stopped before, at and after the transition point in the methane-depletion curve, demonstrated that both pmoA -mRNA was produced as well as substantial cell growth took place already in the initial phase. In addition, type Ia and II MOB displayed markedly different behaviour, which can be interpreted as ecologically different strategies. For the correct interpretation of methane oxidation assays, the use of small time windows is recommended to calculate methane oxidation activities to avoid substantial cell growth.     

Composition of Methane-Oxidizing Bacterial Communities as a Function of Nutrient Loading in the Florida Everglades

Agricultural runoff of phosphorus (P) in the northern Florida Everglades has resulted in several ecosystem level changes, including shifts in the microbial ecology of carbon cycling, with significantly higher methane being produced in the nutrient-enriched soils. Little is, however, known of the structure and activities of methane-oxidizing bacteria (MOB) in these environments. To address this, 0 to 10?cm plant-associated soil cores were collected from nutrient-impacted (F1), transition (F4), and unimpacted (U3) areas, sectioned in 2-cm increments, and methane oxidation rates were measured. F1 soils consumed approximately two-fold higher methane than U3 soils; additionally, most probable numbers of methanotrophs were 4-log higher in F1 than U3 soils. Metabolically active MOB containing pmoA sequences were characterized by stable-isotope probing using 10?% (v/v) (13)CH(4). pmoA sequences, encoding the alpha subunit of methane monooxygenase and related to type I methanotrophs, were identified from both impacted and unimpacted soils. Additionally, impacted soils also harbored type II methanotrophs, which have been shown to exhibit preferences for high methane concentrations. Additionally, across all soils, novel pmoA-type sequences were also detected, indicating presence of MOB specific to the Everglades. Multivariate statistical analyses confirmed that eutrophic soils consisted of metabolically distinct MOB community that is likely driven by nutrient enrichment. This study enhances our understanding on the biological fate of methane being produced in productive wetland soils of the Florida Everglades and how nutrient-enrichment affects the composition of methanotroph bacterial communities.     

CO2浓度增加对长白山森林土壤甲烷氧化影响

大气CO2浓度升高可能对森林土壤的甲烷(CH4)氧化速率产生影响.本文采用开顶箱技术,对连续6年高浓度CO2（500 μmol·mol-1）处理的长白山森林典型树种蒙古栎树下土壤CH4氧化速率进行研究,并利用CH4氧化菌的16S rRNA特异性引物以及CH4单加氧酶功能基因引物分析了土壤中CH4氧化菌的群落结构与数量.结果表明： CO2浓度增高后,生长季土壤甲烷氧化量与对照和裸地相比分别降低了4%和22%;基于16S rRNA特异性引物的DGGE分析表明,CO2浓度增高导致两类甲烷氧化菌的多样性指数降低;CO2浓度增高对土壤中Ⅰ类甲烷氧化菌数量无显著影响,而使土壤中Ⅱ类甲烷氧化菌数量显著减少,功能基因pmoA拷贝数与对照和裸地相比分别降低了15%和46%.CO2浓度增高导致森林土壤甲烷氧化菌数量与活性降低,土壤含水量的增加可能是导致这一现象的主要原因.     

Ethane oxidation by methane-oxidizing bacteria

The relationship between the rates of methane and ethane oxidation by washed suspensions of methane-oxidizing bacteria has been investigated. Considerable differences between bacterial strains were observed. Two closely related Methylomonas strains which differed in their oxidizing capacity were further investigated. The low ethane oxidation rate of one strain could be strongly stimulated by the addition of oxidizable co-substrates, and the presence of ethane stimulated formate oxidation. The other strain had a much higher ethane oxidation rate and stimulation by co-substrates was negligible.Differences between the levels of dissimilative enzymes in cell-free extracts could not be detected. Attempts to produce extracts with methane mono-oxygenase activity failed. When cells were made permeable with chitosan the results suggested that strains with a low ethane oxidizing capacity obtain the required reductant for the mono-oxygenase from endogenous respiration. In strains with a high ethane oxidation rate, the reductant appears to be derived from oxidation of ethanol or acetaldehyde.     

Effect of bovine manure on fecal coliform attachment to soil and soil particles of different sizes

Manure-borne bacteria can be transported in runoff as free cells, cells attached to soil particles, and cells attached to manure particles. The objectives of this work were to compare the attachment of fecal coliforms (FC) to different soils and soil fractions and to assess the effect of bovine manure on FC attachment to soil and soil fractions. Three sand fractions of different sizes, the silt fraction, and the clay fraction of loam and sandy clay loam soils were separated and used along with soil samples in batch attachment experiments with water-FC suspensions and water-manure-FC suspensions. In the absence of manure colloids, bacterial attachment to soil, silt, and clay particles was much higher than the attachment to sand particles having no organic coating. The attachment to the coated sand particles was similar to the attachment to silt and clay. Manure colloids in suspensions decreased bacterial attachment to soils, clay and silt fractions, and coated sand fractions, but did not decrease the attachment to sand fractions without the coating. The low attachment of bacteria to silt and clay particles in the presence of manure colloids may cause predominantly free-cell transport of manure-borne FC in runoff.