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1.
We investigated whether the prey-predator dynamics of bacteria and protozoa were affected by inorganic mercury at concentrations of 0, 3.5 and 15 mg Hg(II) kg soil−1. The amount of bioavailable Hg was estimated using a biosensor-assay based on the mer-lux gene fusion. The numbers of bacterial CFUs on the general medium 1/100 tryptic soy agar (TSA) were significantly decreased when the soil had been amended with Hg. In contrast, no effect was seen on the number of CFUs on the Pseudomonas-specific medium Gould's S1 agar. Protozoan numbers estimated by the most probable number (MPN) method with 1/100 TSB as growth medium were also negatively affected by Hg. The different fractions of protozoa were affected to different degrees suggesting that amoebae were less sensitive than slow-growing flagellates, which again were less sensitive than the fast-growing flagellates. In contrast, Hg did not induce any detectable changes in the diversity of flagellate morphotypes. In the treatment with 15 mg Hg kg−1 a transiently increased number of bacteria was seen at day 6 probably concomitant with a decrease in the numbers of protozoa. This might indicate that Hg affected the prey-predator dynamics in communities of culturable bacteria and protozoa in soil. Furthermore, we showed that the number of Pseudomonas spp. was not affected by Hg whereas the number of bacteria growing on a general medium was.  相似文献   

2.
Abstract

Contamination of agricultural soil by fecal pathogenic bacteria poses a potential risk of infection to humans. For the biosafety control of field soil, soil solarization in an upland field was examined to determine the efficiency of solarization on the inactivation of Escherichia coli inoculated into soil as a model microorganism for human pathogenic bacteria. Soil solarization, carried out by sprinkling water and covering the soil surface with thin plastic sheets, greatly increased the soil temperature. The daily average temperature of the solarized soil was 4–10°C higher than that of the non-solarized soil and fluctuated between 31 and 38°C. The daily highest temperature reached more than 40°C for 8 days in total in the solarized soil during the second and third weeks of the experiment. Escherichia coli in the solarized soil became undetectable (< 0.08 c.f.u. g?1 dry soil) within 4 weeks as a result, whereas E. coli survived for more than 6 weeks in the non-solarized soil. Soil solarization, however, had little influence on the total direct count and total viable count of bacteria in the soil. These results indicate that soil solarization would be useful for the biosafety control of soil contaminated by human pathogens via immature compost or animal feces.  相似文献   

3.
An improved understanding of factors that influence the survival and/or growth of Escherichia coli (E. coli) in soil is essential to allow the formation of land management practices to control the spread of the pathogenic strains of the bacteria, whose transmission to fresh produce is a threat to food safety. Persistence of E. coli in soils held at different water potentials and with carbon additions then subjected to post-freezing incubation temperatures and in the presence of Klebsiella terrigena (K. terrigena) were investigated. Soil samples adjusted to different water potentials (?0.03, ?0.1 and ?1.5 MPa) were inoculated with a multi-antibiotic resistant strain of E. coli (E. coli 2+), which allowed recovery of the organism from soil samples. In addition to manipulation of water content, different C levels were added and samples were frozen for varying lengths of time, thawed and incubated. In freezing studies, initial soil moisture content significantly affected E. coil 2+ survival in soils following thawing, resulting in lower survival rate (k) at water potential of ?0.03 than at ?0.1 and ?1.5 MPa. The effect of length of freezing time was significant only at ?0.03 MPa. Glucose addition at 1.25 mg C g?1 improved survival rate versus glucose at 0.125. The low level glucose increased die-off rate versus no addition, suggesting that unless amendments provide C above a certain threshold level, they might facilitate the death of the bacteria. E. coli 2+ survival improved in the presence of K. terrigena at 6°C but not at 23°C. Persistence of E. coli under the interactive influence of various environmental factors highlights the urgency and importance of understanding its potential for transmission to fresh produce and water bodies.  相似文献   

4.
Contamination of food and water by microorganisms from animal manure has become an important issue in public health. Escherichia coli O157:H7 is one of several emerging pathogens of concern. In this research, we studied how the self-heating, thermophilic phase of composting influenced laboratory-grown vs. bovine-derived E. coli O157:H7 mortality, specifically the relationship between temperature, time at temperature, and pathogen survival. Composting experiments were conducted in laboratory-scale bioreactors operated in three temperature ranges: 40°C to 50°C, 50°C to 60°C, and greater than 60°C. We measured the effects of temperature and composting time on E. coli O157:H7 mortality. Laboratory-grown E. coli O157:H7, inoculated into the initial compost material, were not detected after approximately 300 degree days of heating. In several experiments where compost temperatures did not rise above 50°C, an initial decline of E. coli O157:H7 with subsequent regrowth was observed. E. coli O157:H7 in compost materials from infected cattle were not detected after approximately 180 degree days of heating. Numbers of total coliform bacteria declined with temperature similarly to those of E. coli O157: H7. The results of this research provide information for reducing or eliminating E. coli O157:H7 in animal wastes.  相似文献   

5.
Pseudomonas strains may be used as alternatives to fungicides as some of them produce secondary metabolites, which can inhibit growth of plant pathogenic fungi. Increased knowledge of non-target effects of the antagonistic bacteria on other soil organisms as well as of the survival and predation resistance of the antagonistic bacteria is necessary for risk assessment and increased performance of antagonistic bacteria as biological control agents. In the present study, we aimed to investigate the difference between Pseudomonas spp. with respect to their predation resistance to and effects on the three different and common soil flagellates Bodo caudatus, Cercomonas longicauda, and Neocercomonas jutlandica. Two antagonistic Pseudomonas: Pseudomonas fluorescens CHA0 and P. fluorescens DR54 and two positive control strains: P. fluorescens DSM 50090T and Pseudomonas chlororaphis ATCC 43928 were studied. CHA0, which is reported to produce a range of different antibiotic substances, was inhibitory to all the tested flagellates whereas DR54, which produces viscosinamide, only inhibited the growth rate of B. caudatus. Removal of spent medium from a CHA0 culture reduced the growth inhibition of C. longicauda, although the growth rate was still lowered compared with DSM 50090T. In contrast, removal of spent medium from a DR54 culture had minor effect on C. longicauda. The flagellate B. caudatus was far more sensitive towards the antagonistic Pseudomonas strains of the tested flagellates.  相似文献   

6.
Animal wastes are commonly used in a sustainable manner to fertilize crops. However, manures contain numerous pathogenic bacteria that can impact animal and human health. Treatment of animal waste by anaerobic digestion has the potential to reduce pathogen loading to land. This study was conducted to determine the fate of bacteria applied in raw and anaerobically digested dairy slurries that were broadcast and subsurface applied in a field of forage grasses. Digested slurry had significantly fewer indicator bacteria, Escherichia coli and fecal coliform at time of application. Anaerobic digestion did not increase the survivability of indicator bacteria. Waste treatment and application method did not affect the rate of bacteria die-off. There were fewer E. coli and fecal coliform at the end of each trial in the soils that received digested slurry. Anaerobic digestion of dairy waste has the potential to reduce pathogenic bacteria loading to cropland.  相似文献   

7.
Mycorrhizal (Lactarius rufus Fr.) and non-mycorrhizal Norway spruce seedlings (Picea abies Karst.) were grown in a sand culture and inoculated with protozoa (naked amoebae and flagellates) extracted from native forest soil or with protozoa grown on agar cultures. A soil suspension from which the protozoa were eliminated by filtration or chloroform fumigation was used as a control. After 19 weeks of growth in a climate chamber at 20–22°C, the seedlings were harvested. Protozoa reduced the number of bacterial colony-forming units extracted from the rhizoplane of both non-mycorrhizal and mycorrhizal seedlings and significantly increased seedling growth. However, concentrations of mineral nutrients in needles were not increased in seedlings with protozoan treatment. It is concluded that the increased growth of seedling was not caused by nutrients released during amoebal grazing on rhizosphere micro-organisms. The protozoa presumably affected plant physiological processes, either directly, via production of phytohormones, or indirectly, via modification of the structure and performance of the rhizosphere microflora and their impact on plant growth. Mycorrhizal colonization significantly increased the abundance of naked amoebae at the rhizoplane. Our observations indicate that protozoa in the rhizosphere interact significantly with mycorrhizae.  相似文献   

8.
设施蔬菜栽培长期施用过量化肥,往往导致土壤质量退化及作物产量降低等问题。因此,采用生态友好的农业生产方式已成为农业可持续发展的趋势。本研究在野外调控试验的第3年采集作物和土壤,研究了施用不同有机物料条件下,接种赤子爱胜蚓(Eisenia foetida)对设施菜地土壤性质和作物生长的影响。结果表明,在不同有机物料施用下接种赤子爱胜蚓均显著地提高了黄瓜和菠菜的产量,其中在施用腐熟牛粪+食用菌渣条件下接种赤子爱胜蚓效果最显著。此外,在腐熟牛粪和腐熟牛粪+食用菌渣施用条件下,接种赤子爱胜蚓显著地提高土壤的硝态氮(NO3–-N)、团聚体平均重量直径(MWD)、微生物生物量碳(MBC)、微生物生物量氮(MBN)和代谢熵(q CO2),而在施用商品有机肥的处理中,接种赤子爱胜蚓仅显著地提高了土壤NO3–-N和q CO2。本研究促进了对蚯蚓在设施农业生态系统中服务功能的理解,并为设施农业生产提供了理论基础。  相似文献   

9.
Understanding the survival and persistence of Escherichia coli in soil with different microbial composition is essential for the accuracy of water quality assessment and microbial source tracking. This microcosm experiment was conducted to investigate the survival pattern of three E. coli strains (originated from soil, dog feces and human feces, separately) in soil with modified microbial community composition. Bile salt No. 3 (BS3) of progressively increased density (0.05%, 0.15%, 0.30% and 0.50%) was added into sandy loam soils and incubated for 90 days. Laboratory cultured E. coli were then inoculated into soil and incubated for another 150 days to monitor their survival pattern. Change of bacterial community diversity by BS3 was detected by both cultivation based and cultivation independent (PCR-Denaturing Gradient Gel Electrophoresis) methods. In general, progressively increased BS3 concentration resulted in decreased CFU counts both at 10 days and 90 days incubation. DGGE analysis indicated only a slight change in bacterial community composition at 10 days but a significant change at 90 days. Cluster analysis suggested that BS3 treatment grouped separately from controls. Survival of E. coli in soil was significantly influenced by the complexity of the microbial community, as die-off rate of E. coli progressively declined with the reduction of microbial community diversity. Differential survival of E. coli under different soil microbial stress highlights the importance of incorporating biotic factors in predictive models for water quality management and microbial source tracking study.  相似文献   

10.
 The production of auxins [indoleacetic acid (IAA) and related compounds] by Azospirillum brasilense and Klebsiella pneumoniae in culture media supplemented with tryptophan was investigated. Extracts from the supernatants of cultures incubated for different periods of time were partitioned into two fractions and each fraction was analysed separately by using HPLC. The chromatography was performed by using different optimized mobile phases and corresponding standards. Both N-fixing strains produced high quantities of extracellular IAA and tryptophol. The production of both compounds increased during the stationary phase of the culture. However, very low levels of indoleacetaldehyde and indolepyruvate produced by K. pneumoniae in the exponential phase of the culture, were only recorded when the samples were analysed immediately after the extraction. In addition, the effect of different concentrations of filter-sterilized culture supernatants of both strains on the development of rice roots grown in hydroponic culture medium was studied. Addition of the optimum concentrations (6–8%) of bacterial supernatants to such hydroponic cultures increased root elongation, root surface area, root dry matter and development of lateral roots and root hairs compared to untreated roots. On the other hand, the addition of high concentrations of the supernatant (more than 10%) strongly inhibited root elongation, lateral root development, and caused root outgrowths, i.e. round nodule-like tumours. Received: 7 January 1998  相似文献   

11.
During animal waste agricultural applications, the major concern is pathogen spreading, which may contaminate surface water and groundwater. Among the pathogenic microorganisms found in animal waste, Salmonella typhimurium and Escherichia coli O157:H7 are of particular concern. When transported in sub‐surface agricultural soil, S. typhimurium and E. coli O157:H7 are captured at the air–water–sediment interfaces through physical interactions. Because in situ colloids contribute to the formation of air–water–sediment, their mobilization affects the transport of S. typhimurium and E. coli O157:H7. The impact of irrigation rates on in situ colloid mobilization and S. typhimurium and E. coli O157:H7 transport was investigated in intact soil columns collected from an agricultural site in Gadsden County of Florida, USA. The columns were irrigated with sterilized nano‐pure deionized water to mobilize the colloids in the soil by stepwise increases in flow rate. For each flow rate, after colloids were mobilized and steady state was reached, S. typhimurium and E. coli O157:H7 were introduced. The cumulative amount of released in situ colloids increased linearly with the irrigation rates (R2 = 0.986–0.996) and transport of the bacteria was enhanced after colloid mobilization. Interactions of the bacteria with the sediments and the air‐water interface were characterized: these played an important role in controlling S. typhimurium and E. coli O157:H7 retention in soil.  相似文献   

12.
Hydroponics is an excellent technique for the cultivation of vegetable crops and other plants, but organic fertilizers cannot be used in conventional hydroponic systems, which generally use only inorganic fertilizers, because organic compounds in the hydroponic solutions generally have phytotoxic effects that lead to poor plant growth. Few microorganisms are present in hydroponic solutions to mineralize the organic compounds into inorganic nutrients. In this article a novel and practical hydroponic culture method that uses microorganisms to degrade organic fertilizer in the hydroponic solution has been developed. Soil microorganisms were cultured by regulating the amounts of organic fertilizer and inoculum, with moderate aeration. The microorganisms mineralized organic nitrogen via ammonification and nitrification into nitrate at an efficiency of 97.6%. The culture solution containing the microorganisms was usable as a hydroponic solution, and organic fertilizer could be directly added to it during vegetable cultivation. Vegetables grew well in the organic hydroponic system. Organic hydroponics based on this method is therefore a practical tool for the utilization of organic sources of fertilizer.  相似文献   

13.
不同栽培条件下蔬菜塑料大棚土壤尖孢镰刀菌数量的变化   总被引：5，自引：1，他引：5  
应用尖孢镰刀菌选择性培养基,调查了太湖地区不同蔬菜品种、不同栽培年限、不同栽培方式及不同土壤深度的蔬菜塑料大棚土壤中尖孢镰刀菌数量的变化情况。结果显示,栽种黄瓜的土壤中尖孢镰刀菌数量达1.6×104cfug-1干土,显著大于栽种芹菜和茄子的土壤。随着栽培年限的增加,土壤中尖孢镰刀菌数量有增加的趋势,连作4a土壤中尖孢镰刀菌数量比连作1a土壤增加了22%。与有土栽培相比,基质槽培土壤中尖孢镰刀菌数量较少,仅1.1×104cfug-1干土,基质栽培可能是国内今后蔬菜塑料大棚的发展方向之一。随着土层深度的增加,土壤中尖孢镰刀菌数量逐渐降低,尖孢镰刀菌很少从表层土向下迁移。这些结果为蔬菜塑料大棚土壤的可持续利用提供了一些初步的微生物学依据。  相似文献   

14.
From the results of in vitro studies carried out on wastewater from a stabilization pond it can be concluded that pH values close to 9, as a single factor, do not play any essential role in the die-off of fecal coliform bacteria. The percentage of elmination that occurs in pond water inoculated with 1.1×1010 cells of E. coli mL?1 where the pH is maintained at 8.2 (original pH) is 99.997%, a much greater reduction than that observed (94.1%) in distilled water inoculated with the same concentration of E. coli and where pH is increased up to 9.  相似文献   

15.
Compost water extracts (compost teas) are gaining popularity among organic growers, largely because of their disease suppressive activity when applied to foliage or soil. Production methods often include addition of supplemental constituents, particularly molasses, to stimulate plant-beneficial microbial populations. We have found that molasses amendments also favor regrowth of human pathogenic bacteria, raising public health concerns about potential contamination of treated crops, particularly produce intended for fresh consumption. Using disease outbreak strains marked with green fluorescent protein (GFP) and spontaneous antibiotic-resistance, we found that regrowth of Salmonella enterica serovar Thompson and Escherichia coli O157:H7 was positively correlated with molasses concentration. For Salmonella, regrowth was also dependent on the type of starter compost material used. Salmonella populations increased from 1 at time 0 to over 1000 CFU ml?1 in dairy manure compost tea with 1% molasses, and from 1 at time 0 to over 350,000 CFU ml?1 in chicken manure compost tea by 72 h. E. coli populations increased from 1 at time 0 to approximately 1000 CFU ml?1 in both types of tea by 72 h. Pathogen regrowth did not occur when molasses was eliminated or kept to 0.2%.  相似文献   

16.
Laboratory experiments were carried out to investigate the fate of bacteria during and after passage through the intestinal tract of detritivore earthworms. Earthworms (Lumbricus spp.) were fed with cattle dung inoculated 7 days previously with one of five different Gram-negative bacteria. Bacterial concentrations were determined 2 days later in dung and soil, and in gut material from different parts of the earthworm intestinal tract. A high percentage (28–82%) of the total bacteria (epifluorescence direct counts) in the earthworm gut content was culturable. The concentration of total heterotrophic aerobic bacteria did not vary significantly among the five different bacterial additions and the non-inoculated control. In earthworm casts the number of total heterotrophs per gram dry matter (2.1×109) was higher than in soil (1.7×108), but lower than in the dung (1.5×1010). The test-bacteria, however, showed different survival patterns along the earthworm intestinal tract. The concentrations of Escherichia coli BJ 18 and Pseudomonas putida MM 1 and MM 11 in earthworm casts were lower than in the ingested dung, while concentrations of Enterobacter cloacae A 107 and Aeromonas hydrophila DMU 115 in dung and casts were similar. Ent. cloacae, and to aminor extent E. coli, were reduced in numbers by several orders of magnitude in the pharynx and/or crop. In the hind gut, however, the concentration of Ent. cloacae had increased to the same level as in the ingested dung, while the concentration of E. coli remained low. Our observations indicate that the bacterial flora of ingested food materials changes qualitatively and quantitatively during gut transit.  相似文献   

17.
The distribution of inoculated Escherichia coli cells and indigenous bacteria in a silt loam soil and a sandy soil was studied using fluorescence microscopy techniques. Ethidium bromide stained inoculated cells against the soil and resin background. Satisfactory results were also obtained with epifluorescence microscopy of samples stained with calcofluor white M2R (CFW) and 4′,6-diamidino-2-phenylindole (DAPI). Indigenous soil bacteria were visualized in soil thin sections, after staining with ethidium bromide, using fluorescence microscopy. The density of these bacteria was estimated to be 107-108 cells/cm3. Inoculated E. coli cells, stained with one of the green fluorochromes (fluorescein isothiocyanate (FITC), 5-(4,6-dichlorotriazinyl)aminofluorescein, or eosin Y), could be clearly distinguished in sandy soil thin sections. Confocal laser scanning microscopy with 3D image reconstruction was also successfully applied to characterize distribution of E. coli introduced to soil. The fate of introduced bacteria and the location of indigenous bacteria in soil can be confirmed using the microscopic techniques described in this paper.  相似文献   

18.
The impact of protozoa on the availability of bacterial nitrogen to plants   总被引：9，自引：0，他引：9  
Summary Microbial N from 15N-labelled bacterial biomass was investigated in a microcosm experiment, in order to determine its availability to wheat plants. Sterilized soil was inoculated with either bacteria (Pseudomonas aeruginosa alone or with a suspension of a natural bacterial population from the soil) or bacteria and protozoa to examine the impact of protozoa. Plant biomass, plant N, soil inorganic N and bacterial and protozoan numbers were determined after 14 and 35 days of incubation. The protozoa reduced bacterial numbers in soil by a factor of 8, and higher contents of soil inorganic N were found in their presence. Plant uptake of N increased by 20010 in the presence of protozoa. Even though the total plant biomass production was not affected, the shoot: root ratios increased in the presence of protozoa, which is considered to indicate an improved plant nutrient supply. The presence of protozoa resulted in a 65010 increase in mineralization and uptake of bacterial 15N by plants. This effect was more pronounced than the protozoan effect on N derived from soil organic matter. It is concluded that grazing by protozoa strongly stimulates the mineralization and turnover of bacterial N. The mineralization of soil organic N was also shown to be promoted by protozoa.Communication No. 9 of the Dutch Programme on Soil Ecology of Arable Farming Systems  相似文献   

19.
《Applied soil ecology》1999,11(1):79-90
Escherichia coli K12 strain (J5-3/RP4) persisted in sandy loam for more than 70 days when incubated at 10°C or 4°C. It decreased to below the level of detection within 20 days when incubated at 25°C. No loss of multi-resistance plasmid RP4 from the E. coli cells was detected during incubation in soil. There was a positive relation between the bacterial inoculum size and the following increase of the protozoan numbers in the soil. When soil microcosms were amended with an eukaryotic inhibitor, the period of survival was increased. These observations indicate a direct involvement of protozoa in the decline of E. coli in soil. Transfer of plasmid RP4 from E. coli donor bacteria to indigenous bacteria in soil was detected already 24 h after addition of the E. coli K12 donor strain. The efficiency of transfer during the first 48 h was approximately 10−6 transconjugants per donor. Inhibition of protozoan predation increased the number of transconjugants appearing in the soil, but the transfer efficiency per donor was not affected by the decreased predation. No transfer could be detected when the donor strain was washed and resuspended in saline before addition to the soil, but transconjugants were detected in this experiment when nutrients (LB) were supplemented after two days of incubation. Plasmid RP4 was maintained in the transconjugant soil bacteria throughout the experiment. The data presented here indicate that the indigenous bacteria in soil may serve as a sink for plasmidborne traits.  相似文献   

20.
Abstract

Potherb mustard (Brassica rapa var. nipposinica) and tomato plants (scion, ‘CF Momotaro haruka’; rootstock, ‘Dokutar K’; Solanum lycopersicum) were cultured in hydroponic medium containing cesium-137 (137Cs) at three different concentrations (0.03, 0.13 and 1.03 Bq L?1), and uptake of 137C into the plants was determined. When the 137Cs radioactivity concentration in the medium was 1.03 Bq L?1, the 137Cs radioactivity concentrations in the edible portions of the plants were 4.80 Bq kg?1 fresh weight for the potherb mustard plants and 3.60 Bq kg?1 fresh weight for the tomato plants. In both species, the 137Cs radioactivity concentration in the edible portions decreased with decreasing 137Cs radioactivity concentration in the culture medium. When the 137Cs radioactivity concentration in the medium was 0.03 Bq L?1, a concentration observed in many streams and in tap water in Fukushima Prefecture after the accident at the Fukushima Daiichi Nuclear Power Plant, the 137Cs radioactivity concentrations in the edible portions of the plants were 0.50 and 0.15 Bq kg?1 fresh weight for potherb mustard and tomato plants, respectively. These values are less than the Japanese allowable limit for radiocesium in food. For both species, the transfer factors for 137Cs uptake from the culture media to the edible portions and the average transfer rates over the cultivation period were calculated.  相似文献   

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