Effect of dicumarol on the growth of some soil microorganisms.

The effect of dicumarol on growth of selected soil bacteria: Azotobacter chroococcum, Arthrobacter globiformis, A. citreus and Bacillus megaterium was studied. The following minimum concentrations were inhibitory in vitro: Arthrobacter citreus--20 mug/ml., Bacillus megaterium--40 mug/ml., Azotobacter chroococcum--40 mug/ml. Arthrobacter globiformis--70 mug/ml. Cells of all microorganisms studied grown in the presence of dicumarol developed aberrant morphological forms.     

Ethylene production by soil microorganisms.

Ethylene-producing strains of Penicillium cyclopium and P. crustosum were isolated from soil. These isolates produced ethylene on a variety of carbon growth substrates including phenolic acids. The quantities of ethylene produced on the various substrates varied, and the subtrate-ethylene prosuction pattern for P. cyclopium strains differed significantly from that of P. crustosum strains.     

Infrared color photomicrography of soil microorganisms.

The infrared color photomicrography technique for detecting unstained microbial cells in soil is revised for use with Kodak's recently introduced Ektachrome infrared film. Thes new version of the film required achromatic objectives instead of apochromats, and the use of a blue filter in addition to the previously required red filter. These filters also improve the visual focus capability of the operator. It was found that dry soil smears can be photographed as either immersion oil or aqueous mounts. Several makes of bright-field transmitted-light microscopes gave similar results. Phase microscopy, however, produced deteriorated image quality although the proper 'false' colors were produced.     

Effects of plutonium on soil microorganisms

As a first phase in an investigation of the role of the soil microflora in Pu complex formation and solubilization in soil, the effects of Pu concentration, form, and specific activity on microbial types, colony-forming units, and CO(2) evolution rate were determined in soils amended with C and N sources to optimize microbial activity. The effects of Pu differed with organism type and incubation time. After 30 days of incubation, aerobic sporeforming and anaerobic bacteria were significantly affected by soil Pu levels as low as 1 mug/g when Pu was added as the hydrolyzable Pu(NO(3))(4) (solubility, <0.1% in soil). Other classes of organisms, except the fungi, were significantly affected at soil Pu levels of 10 mug/g. Fungi were affected only at soil Pu levels of 180 mug/g. Soil CO(2) evolution rate and total accumulated CO(2) were affected by Pu only at the 180 mug/g level. Because of the possible role of resistant organisms in complex formation, the mechanisms of effects of Pu on the soil fungi were further evaluated. The effect of Pu on soil fungal colony-forming units was a function of Pu solubility in soil and Pu specific activity. When Pu was added in a soluble, complexed form [Pu(2)(diethylenetriaminepentaacetate)(3)], effects occurred at Pu levels of 1 mug/g and persisted for at least 95 days. Toxicity was due primarily to radiation effects rather than to chemical effects, suggesting that, at least in the case of the fungi, formation of Pu complexes would result primarily from ligands associated with normal (in contrast to chemically-induced) biochemical pathways.     

The effect of turbulent motion on the diffusion of microorganisms

The effect of turbulent fluid motion on the diffusion of simple organisms is discussed. The net reproduction rate and the turbulent flow are assumed to be Gaussian-correlated random variables. For homogeneous istropic turbulence, simple equations for the average concentration of the organisms are derived in terms of the energy density of the fluid. It is shown that the effective diffusivity generated by the motion is positive-definite, and is independent of the helicity of the flow.     

转基因作物对土壤微生物的影响

全球范围内转基因农作物的大量种植不仅带来巨大的经济利益,同时也引发了人们关于转基因作物对包含土壤微生物在内的土壤生态系统的潜在风险的忧虑.转基因作物对土壤微生物的影响包括外源基因表达蛋白对非靶标土壤微生物的直接影响,也包括因外源基因导入而植物根系分泌物组分变化引起的间接影响.目前,对转基因作物的大多数研究表明,转基因作物能引起土壤微生物种群数量和结构的变化.但是,转基因作物对土壤微生物的影响力度有大有小,持续时间有长有短,评价不一.本文综述了不同种类转基因作物对土壤微生物的影响,对转基因作物种类、试验技术和原则等影响评价结果准确性的因素进行了讨论,提出了进一步研究需要注意的问题.     

Molecular characterization of soil microorganisms: effect of industrial pollution on distribution and biodiversity

The present study aimed to investigate variations in the diversity of the indigenous bacterial and fungal populations in contaminated soil. Soil samples were collected from highly contaminated agricultural soil adjacent to an industrial drain in the Nile Delta named the “Defsho” drain, located at the city of Kafr El-Dawar, 20 km south of Alexandria (Longitude 30.12917 and Latitude 31.13972). PCR has become a popular tool for the retrieval of the natural environmental rRNA genes that represent native microbial species. Soil DNA was extracted and the 16S and 18S rRNA genes were amplified using polymerase chain reaction (PCR) and gene cloning. About 5,000 clones were obtained and genotyped using denaturing high performance liquid chromatography (DHPLC) to fingerprinting the biodiversity in the soil. Clones, which give different peaks with DHPLC, were then subjected to partial sequencing. Five prokaryotic and two eukaryotic out of 1,000 recombinant clones were randomly selected and further studied by DNA sequencing analysis. These clones were designated PT and ET for prokaryotes and eukaryotes, respectively. Results confirmed the hazardous effects of pollution on the distribution and biodiversity of soil microorganisms where most of the native beneficial microorganisms were disappeared or non-cultured under these stressed conditions compared to the normal non-polluted soils in the same governorate which is certainly affecting soil fertility and productivity. Five prokaryotic (PT) and two eukaryotic (ET) recombinant clones were randomly selected and further studied by DNA sequence analysis. DNA sequencing revealed that most of the identified bacteria are members of the class Proteobacteria; subdivision Gammaproteobacteria; order Enterobacteriales and family Enterobacteriaceae. Two PT clones (PT2 and PT4) were identified as Shigella flexneri 301-AF499895; members of PT1 and PT3 were related to Escherichia sp. and the uncultured bacterium S000009863 while PT5 was uncultured bacterium-S000331457 in addition to unclassified member of Desulfobacteriaceae, subdivision Deltaproteobacteria. ET1 was uncultured Trichocomaceae clone HC-B1/1-AF548306 and ET2 represents uncultured fungus clone SBS8w47f-AY681463, respectively. In conclusion, the significant decline in the genetic diversity in Defsho soil emphasized the hazardous effect of the industrial pollution on the biodiversity, stability and functioning of the native microbial population. Results also proved the efficiency of molecular characterization as precise and fast techniques for determining soil biodiversity compared to the traditional cultivation methods.