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1.
Samples of soil (25 g) were treated with 1 or 2 ml of propylene oxide, 400 or 800 parts/106 of sodium azide, or autoclaved for 1.5 or 3.0 h. Soil sterilization was achieved by the propylene oxide and autoclaving treatments. Sodium azide inhibited the bacteria and actinomycetes and drastically reduced the fungal population. The autoclaving treatment decreased the soil pH 0.2 unit, while propylene oxide and sodium azide treatments increased it 0.5–1.1 units. Extractable manganous—Mn was increased 2- to 3-fold by all treatments except for a 90- to 120-fold increase in an autoclaved soil; extractable Ca was not affected; and the extractable K changes were slight. Total extractable N was increased 10–20 parts/106, and available P was generally increased by the treatments. Propylene oxide induced the least chemical alterations upon sterilization and is considered an appropriate sterilant to study chemical transformations in soils; but, germination and growth of wheat and alfalfa were retarded in propylene oxide treated soil.  相似文献   

2.

Purpose

Sorption of humic substances on other soil components plays an important role in controlling their function and fate in soil. Sorption of humic substances by individual soil components has been studied extensively. However, few studies reported the sorption characteristic of humic substances on composites of soil components. This study aimed to investigate the sorption characteristics of humic acid on Fe oxide-bacteria composites and improve the understanding on the interaction among humic substance Fe oxide bacteria in soil.

Materials and methods

Humic acid was purchased from Sigma-Aldrich and was purified. Hematite and ferrihydrite were synthesized in the lab. Bacillus subtilis and Pseudomonas putida were cultivated in Luria-Broth medium and harvested at stationary growth phase. Batch sorption experiments were carried out at pH 5.0. Various amounts of humic acid were mixed with 20 mg of Fe oxide, bacteria, or Fe oxide-bacteria composite (oxide to bacteria of 1:1) in 10 mL of KCl (0.02 mol L?1) to construct sorption isotherms. The effects of phosphate concentration and addition order among humic acid, Fe oxide, bacteria on the sorption of humic acid were also studied. The sorption of humic acid was calculated by the difference between the amount of humic acid added initially and that remained in the supernatant.

Results and discussion

The maximum sorption of humic acid on hematite, ferrihydrite, B. subtilis and P. putida was 73.2, 153.5, 69.1, and 56.7 mg C g?1, respectively. The maximum sorption of humic acid on examined Fe oxide-bacteria composite was 28.2–57.2 % less than the predicted values, implying that the sorption of humic acid was reduced by the interaction between Fe oxides and bacteria. The presence of phosphate exerted negligible influence on the sorption of humic acid on bacteria while it inhibited the sorption of humic acid on Fe oxides. On Fe oxide-bacteria composites, inhibiting influences followed by promoting or weak inhibiting effects of phosphate with increasing concentration on the sorption of humic acid were found.

Conclusions

The interaction between Fe oxides and bacteria reduced the sorption of humic acid; moreover, the reduction was greater by the interaction of bacteria with ferrihydrite than that with hematite. Phosphate exerted negligible and inhibiting influence on the sorption of humic acid by bacteria and Fe oxides, respectively. On Fe oxide-bacteria composites, humic acid sorption was initially inhibited and then promoted or weakly inhibited by phosphate with increasing concentration.  相似文献   

3.
The effects of root extracts of four grasses and two legumes and extracts of soils supporting these plants on the growth of five strains of heterotrophic soil bacteria, and on the rate of nitrogen mineralization and nitrification were measured in culture and in soil. All the root extracts inhibited the growth in culture of the five bacteria by 9–98 per cent. The legume-soil and one of the grass-soil extracts did not inhibit bacterial growth. Only two of the grass-soils, Andropogon lectorum and Pennisetum purpureum markedly inhibited the five bacteria. Incubation of soils with extracts of grass roots or grass-soil increased the rates of nitrogen mineralization and nitrification and incubation with legume root and soil extracts increased the rates of nitrogen mineralization and nitrification even further.  相似文献   

4.
There have been few investigations of the possible effects of genetically engineered plants on the microbiota and enzyme activities in flooded soil. We studied the influence of the transgenic rice KeMingDao (KMD) straw on the culturable microbiota and enzymatic activities in a flooded paddy soil under laboratory conditions. KMD contained a synthetic cry1Ab gene from Bacillus thuringiensis under the control of a maize ubiquitin promoter and linked in tandem with the gusA and hpt genes. The results showed that there were only some occasional significant differences (P<0.05) in the number of Colony forming units of aerobic bacteria, actinomycetes and fungi and in the number of anaerobic fermentative bacteria, denitrifying bacteria, hydrogen-producing acetogenic bacteria, and methanogenic bacteria between the paddy soil amended with Bt-transgenic rice straw and with the non-Bt parental rice straw during the early stages of incubation. From d14 to d84 there were significant increases (P<0.05) in soil dehydrogenase and soil neutral phosphatase activity in soils amended with rice straw compared to soil without added straw. The dehydrogenase activity was significantly greatly (almost 1.95-fold) in soil amended with Bt-transgenic straw from d7 to d14 but from d21 to d49 there was significantly greater activity (about 1.47-fold) in the soil amended with non-Bt-straw. There were no apparent differences between the activity of soil neutral phosphatase in the soils to which non-Bt-straw and Bt-straw had been added. However, both soils to which rice straws were added demonstrated significant differences in the number of microorganisms except for aerobic bacteria and enzymatic activities with respect to the control soil throughout the incubation. The above results indicated that the Bt-straw from KMD transgenic rice is not toxic to a variety of culturable microorganisms in the studied flooded paddy soil.  相似文献   

5.
A broad-spectrum endophyte, Phomopsis liquidambari, was used as a microbial agent to determine the effects of rapid litter decomposition on soil phenolic compounds dynamics, the soil microbial community balance and plant growth. The litter decomposition ratio was closely correlated with lignin degradation. The soil phenol concentration increased with the acceleration of litter decomposition after the first 30 days and later decreased to below the initial level. Based on denaturing gradient gel electrophoresis (DGGE) analysis, soil bacteria, especially gram-negative bacteria that have the potential to degrade aromatic compounds, were found in high abundance when the soil phenol concentration was high. When the phenolic concentration decreased, soil fungi increased in abundance. With fungal application, seed germination significantly increased to 69.87% and seedling growth was enhanced. Rapid litter decomposition by Pho. liquidambari initially led to higher releases of phenolic allelochemicals, which led to the enrichment of soil gram-negative bacteria. In addition, increased soil nutrients and temporarily higher concentrations of phenolics from litter decomposition strengthen seedling growth, suggesting that the endophytic fungus Pho. liquidambari is a suitable candidate for remediation of long-term cropping soil.  相似文献   

6.
A combination of culture-independent and culturing methods was used to assess the diversity of soil bacterial communities from four locations along 77 °S in Victoria Land, Antarctica. Soil samples were from the coast at Marble Point, in the Wright Valley from Bull Pass and near Lake Vanda, and from Mt. Fleming near the polar plateau. Total carbon and nitrogen, and water content of the soils were low, whereas total P was very high. The pH of the soils varied from extremely alkaline to slightly acid and electrical conductivity was medium to high on the coast and very high in inland soils from Bull Pass and Mt. Fleming. The average monthly air temperature was similar (−18 °C to −24 °C) at all the sites; however, in summer surface soil temperatures were >0 °C at Marble Point and in the Wright Valley for a total of 1100 and 1700 h, respectively. Marble Point soil had the most potential to support bacterial growth and activity with a mean total of 310 h per year when surface soils had a liquid volumetric soil moisture content >5%. Highest counts of culturable heterotrophs occurred in soil from Marble Point, whereas Mt. Fleming soil contained few organisms and had no liquid soil moisture recorded. Seven hundred and twenty-eight clones and 71 bacterial isolates were screened by restriction fragment length polymorphisms, and representatives of those dominant ribotypes that occurred more than 3 times were sequenced. The dominant ribotypes grouped within the bacterial divisions Bacteroidetes, Actinobacteria, Proteobacteria, Thermus-Deinococcus, Acidobacteria, Firmicutes and Cyanobacteria. The closest relatives of the amplicon library clones or cultured bacteria include the genera Hymenobacter, Gillisia, Arthrobacter, Rubrobacter, Friedmanniella, Deinococcus and Leptolyngbya. Many of the clones and bacteria were most similar to others from Antarctic sources, in particular a cyanobacterium-dominated cryptoendolithic community in Beacon sandstone. Some ribotypes were more prevalent in drier soils of the Wright Valley, including relatives of Deinococcus, Rubrobacter and clone FBP460 from Beacon sandstone. Bacterial communities from Marble Point soils were more diverse than those of the Wright Valley. Very few bacteria were isolated from Mt. Fleming soil.  相似文献   

7.
Sodium N-methyldithiocarbamate (metam sodium) and 1,3 dichloropropene are widely used in potato production for the control of soil-borne pathogens, weeds, and plant parasitic nematodes that reduce crop yield and quality. Soil fumigation with metam sodium has been shown in microcosm studies to significantly reduce soil microbial populations and important soil processes such as C and N mineralization. However, few published data report the impact of metam sodium on microbial populations and activities in potato production systems under field conditions. Fall-planted white mustard (Brassica hirta) and sudangrass (Sorghum sudanense) cover crops may serve as an alternative to soil fumigation. The effect of metam sodium and cover crops was determined on soil microbial populations, soil-borne pathogens (Verticillium dahliae, Pythium spp., and Fusarium spp.), free-living and plant-parasitic nematodes, and C and N mineralization potentials under potato production on five soil types in the Columbia Basin of Eastern Washington. Microbial biomass C was 8–23% greater in cover crop treatments compared to those fumigated with metam sodium among the soil types tested. Replacing fumigation with cover crops did not significantly affect C or N mineralization potentials. Cumulative N mineralized over a 49-day laboratory incubation averaged 18 mg NO3-N kg−1 soil across all soil types and treatments. There was a general trend for N mineralized from fumigated treatments to be lower than cover-cropped treatments. Soil fungal populations and free-living nematode levels were significantly lowered in fumigated field trials compared to cover-cropped treatments. Fumigation among the five soil types significantly reduced Pythium spp. by 97%, Fusarium spp. by 84%, and V. dahliae by 56% compared to the mustard cover crop treatment. The percentage of bacteria and fungi surviving fumigation was greater for fine- than coarse-textured soils, suggesting physical protection of organisms within the soil matrix or a reduced penetration and distribution of the fumigants. This suggests the potential need for a higher rate of fumigant to be used in fine-textured soils to obtain comparable reductions in soil-borne pathogens.  相似文献   

8.
Soil–atmosphere exchange of H2 is controlled by gas diffusion and the microbial production and oxidation activities in soil. Among these parameters, the H2 oxidation activity catalyzed by soil microorganisms harboring high affinity hydrogenase is the most difficult variable to parameterize because it is influenced by many unknown edaphic factors that shape microbial community structure and function. Here we seek to formulate a model combining microbiological and physicochemical variables to predict the H2 oxidation rate (u) in soil. Soil sample replicates collected from a grassland and three forests exhibited different H2 oxidation potentials. We examined the microbial community structure based on ribotyping analysis, the relative abundance of high affinity H2-oxidizing bacteria (HOB) estimated by qPCR and soil physicochemical characteristics as predictors for u. A single linear regression parameterized by total carbon content and a multiple linear regression using total carbon content and HOB relative abundance in soil explained 66 and 92% of the variance in u, respectively. Microbial community composition based on 16S rRNA gene pyrosequencing profiles was not a reliable predictor for u. Indeed, we found that HOB are members of the rare biosphere, comprising less than 1% of total bacteria as estimated by qPCR. We confirmed this relationship of u with total carbon content and HOB by an independent soil survey of 14 samples collected from maize monocultures, grasslands, deciduous forests and larch plantations. Observations made from both soil surveys thus were combined to build a predictive model for u parameterized with total carbon content and HOB relative abundance. Our results show that molecular biogeochemistry is a potential approach to improve performance of classical H2 surface flux models which estimate u empirically without considering variation in HOB distribution and activity in soil.  相似文献   

9.
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   

10.
Microorganisms (348 fungi, 388 actinomycetes and 319 bacteria) were isolated from a nodulation problem soil, a non-problem virgin soil, a cultivated problem soil and the rhizosphere of clover plants grown in the problem soil. Rhizobium trifolii TA 1 which failed to establish in problem soils was inhibited on laboratory media by a greater number of these soil microorganisms than the better soil colonizing R. trifolii (WU95 and WU290) and R. lupini (WU425). R. lupini was not inhibited or stimulated on agar by many soil or rhizosphere isolates. R. meliloti showed greater stimulation than either R. trifolii or R. lupini and was inhibited by relatively few soil microorganisms so that its poor soil survival was thought to be due to chemical or physical soil conditions rather than to biotic factors. The greatest incidence of rhizobial inhibitors, mainly associated with TA 1, was found among the isolates from the clover rhizosphere. There was a reduction in the relative numbers of rhizobial inhibitors isolated from the cultivated soil compared with the virgin problem soils, a result possibly due to the changed soil environment changing with cultivation, altered vegetation and the addition of superphosphate. Inhibitors of rhizobia were more frequent amongst the bacteria than fungi or actinomycetes. Strong stimulation was more commonly shown by fungi than by actinomycetes or bacteria. The interaction on agar between rhizobia and the soil microflora is related to soil colonization and persistence.  相似文献   

11.
Blending, shaking with a mechanical wrist-action shaker or ultrasonication were compared for removing bacteria from a sandy soil and a silt loam soil. Bacteria were counted microscopically after staining with acridine orange. There was no significant difference in the numbers of bacteria released from the sandy soil by the different treatments but ultrasonication extracted more bacteria from the silt loam. Highest recoveries of bacteria were obtained with a combination of Tris buffer as extractant, and 25% Ringer's solution as diluent. Ultrasonication of an irradiated sandy soil containing added Bacillus cereus removed 97% of the bacteria from the sand grains, but lysed some cells. Members of the indigenous soil population were more firmly held by the soil than added bacteria. Optimum conditions for recovering soil bacteria by ultrasonication were either 10.5 μm for 30s or 5 μm for 2 min. With the natural population, the numbers of bacteria and the proportion of metabolizing bacteria increased a little after ultrasonication as shown by labelling cells with 3H-glucose and detecting uptake by autoradiography. However, three isolates of bacteria tested showed varying amounts of injury after ultrasonication, with 5 μm for 2 min causing more damage than 10.5 μm for 30s. Ultrasonication was a more efficient means of extracting the natural bacterial population of soil than shaking but the time and amplitude must be adjusted to avoid injury to cultured bacterial cells.  相似文献   

12.
Biphenyl and several plant secondary metabolites (PSM) (carvone, isoprene, limonene, naringin, and coumarin) and surfactant (hydroxypropyl-β-cyclodextrin, (HP-β-CD)) have been shown to improve aerobic polychlorinated biphenyl (PCB) removal by several bacterial species. The objective of this study was to determine whether these treatments also affect PCB removal and microbial community structure in a high organic matter soil (Pahokee soil series with 67% organic matter) and low organic matter soil (Woolper soil series with 6% organic matter), as determined by monitoring changes in PCB levels and phospholipid fatty acids (PLFA) profiles in laboratory microcosms amended with these compounds. Biphenyl enhanced di-chlorinated and tri-chlorinated biphenyl removal in both soils, but PSM did not improve removal of these congeners. On the contrary, HP-β-CD decreased PCB removal when used in combination with biphenyl. Two-way analysis of variance indicated that HP-β-CD significantly increased tetra- and penta-chlorinated biphenyl removal from the high organic matter soil, but not from the low organic matter soil. Principal components analysis of PLFA data indicated that HP-β-CD increased proportions of 18:1ω7c associated with Gram-negative bacteria, but decreased 10me16 and 10me17 lipid associated with Gram-positive bacteria, while biphenyl and PSMs had no detectable effects on soil microbial communities. PCB removal was not correlated to any PLFA. In conclusion, PSM previously shown to enhance PCB removal in soil-free systems were not effective in two divergent soils evaluated in this study, and HP-β-CB had increase, decrease, or no effect on PCB removal depending on types of PCB congeners, soils, and co-amendments.  相似文献   

13.
Microbial biomass is an important source of soil organic matter, which plays crucial roles in the maintenance of soil fertility and food security. However, the mineralization and transformation of microbial biomass by the dominant soil macrofauna earthworms are still unclear. We performed feeding trials with the geophagous earthworm Metaphire guillelmi using 14C-labelled bacteria (Escherichia coli and Bacillus megaterium) cells, fungal (Penicillium chrysogenum) cells, protein, peptidoglycan, and chitin. The mineralization rate of the microbial cells and cell components was significantly 1.2–4.0-fold higher in soil with the presence of M. guillelmi for seven days than in earthworm-free soil and 1–11-fold higher than in fresh earthworm cast material. When the earthworms were removed from the soil, the mineralization of the residual carbon of the microbial biomass was significantly lower than that in the earthworm-free soil, indicating that M. guillelmi affects the mineralization of the biomass in soil in two aspects: first stimulation and then reduction, which were attributed to the passage of the microbial biomass through the earthworm gut, and that the microorganisms in the cast could play only minor roles in the stimulated mineralization and residual stabilization of microbial biomass. Large amounts (8–29%) of radiolabel of the tested microbial biomass were assimilated in the earthworm tissue. Accumulation of fungal cells (11%) and cell wall component chitin (29%) in the tissue was significantly higher than that of bacterial cells (8%) and cell wall component peptidoglycan (15%). Feeding trails with 14C-lablled microbial cells and cell components provided direct evidence that microbial biomass is a food source for geophagous earthworm and fungal biomass is likely a more important food source for earthworms than bacterial biomass. Findings of this study have important implications for the roles of geophagous earthworms in the fate of microbial biomass in soil.  相似文献   

14.
Here, we report results from a field experiment investigating the application of biochars, lime, organic fertilizer, and their combinations. Soil pH was increased by ameliorants. Wheat biochar produced the largest increase, of approximately 2 pH units, and mixed treatment (one third rice husk biochar, one third lime, and one third organic fertilizer) also caused large increases, of almost 1 pH unit. There was strong evidence that the ratio of ammonia-oxidizing archaea to ammonia-oxidizing bacteria (AOB) abundance greatly increased with decreased soil pH, indicating that soil pH was an important factor affecting the abundance of AOB. High-throughput MiSeq sequencing showed that the soil ameliorants significantly increased the relative abundances of Nitrosomonas and Nitrospira. Soil pH was an important determinant of the bacterial community composition and diversity. Our study suggests that the ameliorants (biochar, lime, organic fertilizer, and their combinations) change soil nitrification by altering nitrifying bacteria abundance, diversity, and composition, caused by the changed soil pH.  相似文献   

15.
Lasiurus sindicus is a highly nutritive, drought tolerant, perennial grass, endemic to the Thar Desert of Rajasthan, India. In order to characterize the diversity of bacteria associated with roots of this grass that had survived severe drought stress, 16S-rRNA gene clone libraries were established from RT-PCR amplified products of the total RNA extracted from the washed roots and rhizosphere soil samples. Eight major bacterial taxa were identified in a total of 121 16S-rRNA gene clones. The majority of sequences belonged to Gram-positive bacteria, Actinobacteria being the most predominant ones, closely followed by Firmicutes. Most of the sequences showed similarity with sequences from cultivated bacteria or uncultivated environmental clones associated with arid, semi-arid environments, cold deserts and contaminated soils. PCR amplification of nifH genes using total DNA as template produced a total of 48 nifH clones from the rhizosphere soil and root samples and revealed a predominance of nifH sequences closely affiliated to Pseudomonas pseudoalcaligenes, isolated in a previous study from root samples of Lasiurus sindicus. Some nifH sequences showed close similarity to cultivated diazotrophs like Azospirillum brasilense, Rhizobium sp., and a variety of uncultured nitrogen fixing bacteria. Thus, this study provides us with evidence that L. sindicus harbors a diversity of bacteria with potential for nitrogen fixation.  相似文献   

16.
Micro-aggregates containing sulfate-reducing bacteria in a paddy-field soil were examined by enumerating the number of sulfate-reducing bacteria liberated when the soil was subjected to repeated washings with and without pretreatment by sonication. Soils sampled from both an oxidized surface-layer and a reduced plough-layer were subjected to repeated washings.The liberation of sulfate-reducing bacteria, expressed as log n, were calculated according to the equation Ni = N0 (1/n)i. Where i is the number of repeated washings; N0 is the number of cells per 1 ml supernatant of original soil suspension; Ni is the number of cells per 1 ml supernatant of the i-th wash, and n is the reciprocal of dilution rate. Ideally log n is 1.0 with our conditions.In the case of soils without sonic pretreatment, the values of log n were 0.009–0.018 for sulfate-reducing bacteria, indicating that almost constant numbers of sulfate-reducing bacteria were newly liberated by every wash, and 0.35–0.55 for aerobic bacteria, indicating that a direct wash-out of cells took place. With sonicated soils we obtained the values 0.26–0.38 and 0.39–0.55 respectively.Based on these results we conclude that sulfate-reducing bacteria were present in aggregates which were decomposed by sonic treatment, whereas aerobic bacteria were not.  相似文献   

17.
A range of New Zealand soils, many contaminated by sodium fluoroacetate (“Compound 1080” or NaFA) were examined for micro-organisms capable of defluorinating this animal poison. Species of Pseudomonas and Fusurium capable of growth on NaFA were isolated whilst many other soil bacteria and fungi exhibited defluorinating activity when grown on an alternative organic C source. It was concluded that NaFA has a short biological half-life in the soils investigated.Some NaFA-contaminated soils also contained species of the algae Chlorella and Chlamydomonas which were unaffected by NaFA but growth of a duck weed, Spirodela oligorrhiza, was inhibited 73% in the presence of 5 μM-NaFA.  相似文献   

18.
Bacteria play important roles in mineral weathering, element mobilization, and soil formation. However, little is known about the mineral-weathering bacteria in subsurface soil environments. In this study, a total of 360 bacterial isolates were isolated from the different horizons of a soil profile and characterized for their mineral-weathering abilities and diversity along the soil profile. Among the 360 isolates, 226 isolates were found to have the ability to weather biotite. The average of released Fe, Si, and Al were significantly higher by the isolates from deeper horizons than from upper horizons. Although the proportion of the highly effective Fe solubilizers was not significantly different among the different horizons, the proportion of the highly effective Si and Al solubilizers was significantly higher in the deeper horizons than in the upper horizons. Furthermore, the element-releasing patterns of the mineral-weathering bacteria were different among the different horizons. Most of mineral-weathering bacteria from the soil profile could significantly lower the culture medium pH in the mineral-weathering process. The diversity of the mineral-weathering bacteria was higher in the upper horizons than in the deeper horizons. The weathering bacteria belonged to 12 bacterial genera, among which Burkholderia, Bacillus, and Lysinibacillus were the dominant and high-efficient weathering bacteria. The results showed the depth-related changes in the weathering capacity and community structures of the culturable mineral-weathering bacteria and suggested the possible roles of the bacteria in the mineral-weathering and element mobilization along the soil profile.  相似文献   

19.
应用两相分离技术研究红壤微生物组成的探讨   总被引：1，自引：0，他引：1  
采集了鄂南不同母质和利用现状的6个红壤样，用2％PEG＋6％Dextran两相分离技术（Aqueous two-phase partitioning technique，简写为A2PP）纯化细菌，测定细菌生物量，研究两相分离技术在土壤微生物研究领域的可应用性。结果表明：（1）采用0．1％胆酸钠、钠型离子交换树脂、玻璃珠与土壤一起在4℃下振荡2h，能较好地分散土壤细菌。供试土样细菌分离率介于0．41。0．60之间，不同母质发育的红壤相比，细菌分离率高低依次为：砂页岩〉花岗岩〉第四纪红色粘土；（2）A2PP技术能较好地纯化土壤中的细菌。6个供试原样的细菌多与土壤颗粒及有机质结合在一起，而两相分离技术能够得到较为纯净的细菌个体，土样细菌大多被分离存在于PEG相中，纯化率为63％～78％；细菌提取率介于0．31-0．48，不同母质发育土壤细菌提取率顺序与细菌分离率顺序相同；（3）供试土样的细菌形态都以小球状、小杆状细菌为主。  相似文献   

20.
《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   

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