Simulation of transport through soil of E. coli derived from livestock slurry using the macro model

Abstract. Leaching of faecal coliforms to rivers, lakes and groundwater following the spreading of animal slurry on land is of environmental and public health concern. A two-stage approach was adopted to modelling the transport processes by which Escherichia coli passes through the soil to receiving waters via field drains. First, parameter values were selected for the dual-porosity contaminant transport model macro to simulate through-soil flows, sorption and die-off of E. coli . These simulations reproduced experimental measurements showing rapid flows of the microorganisms to field drains after slurry spreading, which could be explained in terms of macropore flow in which trapping of colloids such as E. coli does not take place. Second, a series of predictive simulations was carried out to test the influence of soil and weather conditions on E. coli losses. These showed that losses are strongly influenced by soil wetness conditions at the time of spreading, and to a lesser degree by rainfall occurring soon after spreading. Selection of spreading 'workdays' with particular weather and soil wetness conditions is beneficial, which indicates opportunities for substantial reductions in the environmental risks of water pollution by E. coli and other faecal microorganisms.     

Relative risk of surface water pollution by E. coli derived from faeces of grazing animals compared to slurry application

Abstract. This article examines some of the factors that influence the relative risk of Escherichia coli pollution of surface waters from grazing animals compared to cattle slurry application. Drainage water from pipe‐drained plots grazed with sheep (16 sheep + lambs per hectare) from 29 May to 17 July 2002 had average E. coli counts of 11 c.f.u. mL^?1 or 0.4% of estimated E. coli inputs over the grazing period. Drainage water from plots on the same site treated with cattle slurry (36 m³ha^?1 on 29 May 2002) had lower average E. coli counts of 5 c.f.u. mL^?1 or 0.03% of estimated faecal input. Sheep (16 lambs per hectare) grazing under cooler, moister conditions from 24 September to 3 December 2001 gave drainage water with much higher average E. coli counts of 282 c.f.u. mL^?1 or 8.2% of estimated input, which is more than twice the average E. coli counts previously reported under such conditions (Vinten et al. 2002 Soil Use and Management 18, 1–9). Laboratory studies of runoff from soil slabs after slurry application showed that the mobility of E. coli in surface soil decreased with time, suggesting that increased attachment to soil or migration to ‘immobile’ water also provides at least part of the physical explanation for the relatively higher risk of pollution from grazing animals compared with slurry. Sampling for E. coli in field drainflow and in streamwater during a storm event in the predominantly dairy Cessnock Water catchment, Ayrshire, Scotland supported the hypothesis that E. coli transport is linked to grazing animals. For a 7‐mm rainfall event, roughly 14% of the estimated daily input from grazing livestock was transported to the river, even though little slurry spreading had occurred in the catchment in the previous month. Spot sampling of field drains in grazed fields and silage fields in the same catchment also showed that grazing animals were the principal source of E. coli and faecal streptococci.     

Effects of deer grazing and fence-line pacing on water and soil quality

Abstract. We studied the effects of red deer grazing and fence-line pacing on soil losses of contaminants (suspended sediment, Escherichia coli , phosphorus) and nitrogen species (ammonia, nitrate) via overland flow and soil physical properties (macroporosity, bulk density, saturated hydraulic conductivity, K _sat) soon after (1 day) and 6 weeks after grazing on a Pallic pastoral soil in southern New Zealand. Fence-line pacing decreased the soil volume occupied by water, macroporosity and K _sat, while increasing suspended sediment (to 0.226 g 100 mL⁻¹), total P (to 2.0 mg L⁻¹), mainly as particulate P (up to 90% of total P), and E. coli (to 3.52 log₁₀ c.f.u. 100 mL⁻¹) concentrations in overland flow at 1 day after grazing compared with soils from the rest of the paddock (0.148 g 100 mL⁻¹, 0.86 mg L⁻¹ and 2.86 log₁₀ c.f.u. 100 mL⁻¹, respectively). Although concentrations in overland flow were less at 6 weeks after grazing than at 1 day after grazing, losses of P, especially in fence-line soils, were still above recommended limits for surface water quality. Compared to P, losses of N species would be unlikely to have a significant impact on downstream water quality. Management strategies should be directed towards minimizing the occurrence of fence-line pacing to prevent contaminant loss and maintain water and soil quality.     

利用介质阻挡放电等离子体杀灭鲜榨果汁大肠杆菌

与传统热杀菌相比,非热杀菌能较大程度地保持食品中营养成分,节约能耗。为了进一步研究非热杀菌技术,利用自行设计的介质阻挡放电反应器（DBDR）,以鲜榨果汁为杀菌介质,研究了DBDR所产生的低温等离子体（LTP）的杀菌效果和对鲜榨果汁品质的影响。采用响应面法建立了介质阻挡放电等离子体（DBDP）杀灭鲜榨果汁饮料中大肠杆菌的二次多项数学模型,验证了模型的有效性,并探讨了循环次数、pH值、温度及电压对DBDP杀灭大肠杆菌的影响,优化出杀灭7个数量级大肠杆菌（E.coli）ATCC 8739的工艺参数为：循环次数6次,pH值 3.14,温度39.72℃,电压21.42 kV。为进一步研究DBDP的杀菌规律和探讨杀菌机理奠定了数学基础,同时,此模型的决定系数R2达到0.9817,可推广应用到其他果蔬汁的杀菌处理,提高鲜榨果蔬汁的品质和质量安全。     

Sherlock MIS系统鉴定土壤中大肠杆菌O157∶H7的研究

<正>污水灌溉和人畜粪肥施用一直是国内外农业中有机废弃物资源化利用的重要途径,这种现象在我国尤为普遍。然而,生活污水含有大量细菌,工业和医院废水更是富含各种病原体,污泥、垃圾和粪肥均可能携带大量病原微生物和寄生虫卵。显而易见的是,这些有害生物种群可随污水灌溉和粪肥施用进入环境中,并通过污染土壤、水源、大气和农畜产品等途径传播或"引燃"疫情的爆发,从而对     

重组大肠杆菌表达降氰酶的诱导条件优化

采用积分光密度法对产碱杆菌（Alcaligenes sp.）降氰酶基因在大肠杆菌中的高效表达进行了诱导条件优化,以工程菌BL21（DE3）-pET28a-cdE的诱导表达条件进行优化,以提高目的蛋白的产量和活性。结果显示,重组菌表达降氰酶的最佳诱导条件为温度28℃,初始菌体浓度OD600值为0.6,IPTG浓度为0.8mmol/L,诱导时间12h。研究发现,诱导剂的添加浓度对外源蛋白的表达水平具有显著影响,使用终浓度为0.8mmol/L的IPTG,诱导表达12h,降氰酶蛋白收率达到143.27mg/L,比活力达到11560 U/mg。与不添加诱导剂相比,重组蛋白的收率和比活力分别提高了64倍和9倍。     

蚯蚓粪中乳酸菌的分离及其在大肠杆菌O157：H7中的抗菌活性

本研究利用SL培养基从蚯蚓粪中分离到54株具有产酸性能的菌株,并以E.coli O157：H7（EDL933株）作为指示菌株,采用点种法检测分离菌株的抑菌活性。结果表明其中6个菌株对指示菌具有拮抗作用,通过形态特征,结合16S rDNA序列分析,初步鉴定该6个菌株分别为食物魏斯特菌（Listeria welshimeri）、乳酸片球菌（Pediococcus acidilactici）、短乳杆菌（Lactobacillus brevis）和格氏乳球菌（Lactococcus garvieae）。分离到的乳酸菌对E.coli O157：H7（EDL933株）具有显著的抑制作用,发酵温度和初始pH值影响发酵液的抑菌作用,优化环境因子可以促进拮抗菌对E.coli O157：H7的抑制作用。本研究为进一步分离抗菌产物用于人畜共患病的预防和治疗提供了理论依据。     

Effect of the expression of Escherichia coli fhuA gene in Rhizobium sp. IC3123 and ST1 in planta: Its role in increased nodule occupancy and function in pigeon pea

The inability to utilize a fungal siderophore as source of iron nutrition by most of the rhizobial cultures isolated from pigeon pea, could be considered a negative fitness factor since hydroxamate siderophores are found in significant amounts in natural soils. Thus these cultures were engineered to use ferrichrome a prototype of hydroxamate type siderophore. Pigeon pea Rhizobium spp. IC3123 and ST1 harboring Escherichia coli fhuA gene, responsible for uptake of Fe³⁺-ferrichrome, were obtained by transformation with pGR1, a broad host range plasmid carrying the fhuA gene under the control of the lac promoter of E. coli. Expression of fhuA in transformed rhizobial strains IC3123::pGR1 and ST1::pGR1 was confirmed by the ability of the plasmid-bearing strains to utilize iron bound to ferrichrome. Inoculation of pigeon pea plants with fhuA expressing rhizobial strains in pot experiments showed a significant increase in plant growth as well as nodule density as compared to those inoculated with the parent as well as the empty vector-bearing strain. Inoculation of pigeon pea seedlings with IC3123::pGR1 and ST1::pGR1 led to marked increase in shoot fresh weight, nodule number per plant, chlorophyll content of leaves and effective nodule symbiosis when compared with plants inoculated with the parent strains IC3123 and ST1. The positive effect of IC3123::pGR1 and ST1::pGR1 treatment on plant growth was more significantly observed when ferrichrome producing Ustilago maydis, known to secrete ferrichrome, was co-inoculated along with the transformed rhizobia. The presence of fhuA gene in rhizobial strains also led to an increased survival and root colonization.