摘要:

The goal of this paper was to demonstrate whether natural transformation could occur in the environment to promote horizontal gene transfer between bacteria. Microcosms consisting of clay, clay and humic acids, or sterile soil were compared with respect to the natural transformation ofPseudomonas stutzeriby mineral-adsorbed DNA. Genes conferring resistance to tetracycline and ampicillin were first inserted inP.stutzeripp100 chromosome via the pSUP202 suicide plasmid. Then, DNA extracted from the engineeredP.stutzeristrain was used for transformation experiments, allowing the new transformed cells to be detected by hybridization with atetprobe. It turned out that DNA adsorbed on clay or soil particles and in presence of humic acids still transformed competent cells with frequencies up to 10−8transformants/viable cell. Finally, natural transformation assays involving two different DNAs were carried out in sterile soil microcosms. The use of nonisogenic DNA extracted from a rifampicin-resistantPseudomonas fluorescensstrain resulted in production of transformants, while isogenic DNA from our engineered strain failed to produce any. These observations confirmed that extracellular DNA adsorbed on a soil matrix composed of minerals and organic matter could still transform competent bacteria under environmental conditions.Key words: transformation,Pseudomonas stutzeri, soil microcosm, DNA, suicide plasmid.

ISSN:0008-4166    

DOI:10.1139/m97-011

出版商:NRC Research Press    

年代:1997

数据来源: NRC

摘要:

A study on ectomycorrhizae and mycorrhizal fungi ofPinus kesiya(Royle ex Gordon) in 2-, 4-, 11-, and 17-year-old pine plantations was carried out. Thirteen mycorrhizal fungi forming ectomycorrhiza with khasi pine were observed. Diversity index of mycorrhizal fungi was directly proportional to the age of the pine stand. The maximum number of fungal species was observed in the oldest stand. Evenness of the sheathing mycorrhizal fungi was also increased with the increase in age of pine. The sporocarps ofBoletus luteus,Scleroderma aurantium,Tricholoma saponaceum, andHygrophorus limacinuswere observed as an early colonizing fungi withPinus kesiya. However, in older plantationsRussula lepidaandAmanita phalloideswere observed as late stage fungi.Boletus luteusandScleroderma aurantiumwere dominant species in all the pine stands. Sporocarps of mycorrhizal fungi were maximum during the rainy season and minimum during the winter months. A positive correlation was observed between the number of ectomycorrhizae and mycorrhizal infection with soil moisture, soil pH, total nitrogen, available phosphorus, exchangeable potassium, and organic matter of the soil. The number of sporocarps exhibited a positive significant correlation with soil moisture content in all the plantations.Key words: ectomycorrhiza, fungi, physicochemical characters,Pinus kesiya.

ISSN:0008-4166    

DOI:10.1139/m97-012

出版商:NRC Research Press    

年代:1997

数据来源: NRC

摘要:

Hammerhead ribozymes are potentially important tools for suppressing intracellular expression of unwanted RNAs. However, the reports that exist on their activity against different targets have described mixed success. As an initial step towards developing a rapid and effective system for in vivo testing of ribozymes, two human immunodeficiency virus type-1 (HIV-1) polymerase (Pol) mRNA-specific ribozymes, RzProdirected against the protease (Pro) coding region and RzRTdirected against the reverse transcriptase (RT) coding region, were designed and tested inEscherichia coli. Both ribozymes displayed similar efficiencies in cleaving their target RNAs in vitro. RNA polymerase chain reaction was adapted to demonstrate the in vivo cleavage of RzProand RzRTtarget sites. The resultant drop in HIV-1 RT activity was measured as well. The degree of suppression of RT activity was more apparent in vivo in cells expressing RzRT. The RT activity in cells expressing RzRTwas shown to decrease by up to 96%. This system will be useful for rapid screening of (i) other ribozyme target sites within the Pol mRNA so that multitargeted ribozymes could be designed for use in anti-HIV-1 gene therapy, (ii) ribozymes with improved stability and catalytic activity, and (iii) cofactors, if any, that could enhance ribozyme activity in vivo.Key words: HIV, hammerhead ribozyme, protease, reverse transcriptase.

ISSN:0008-4166    

DOI:10.1139/m97-013

出版商:NRC Research Press    

年代:1997

数据来源: NRC

摘要:

A microbial population that biodegradedN-phosphonomethyliminodiacetic acid (PIA), a key component of glyphosate (N-phosphonomethylglycine) process waste, was established. The stoichiometric conversion of PIA to aminomethylphosphonic acid (AMPA) was observed in a laboratory sequencing batch reactor (SBR) containing activated sludge from a glyphosate-manufacturing facility and PIA as sole source of carbon. PIA degradation was determined by high-performance liquid chromatography and confirmed by radiolabeled studies. Greater than 90% of the [carboxymethyl-2-14C]-label of PIA was released as14CO2in 7 days using samples of sludge from the SBR. The cycle time required to biodegrade up to 7.5 mM PIA in SBRs was reduced from 21 to < 3 days. PIA biodegradation was also established in an immobilized bacteria column inoculated with mixed liquor from a SBR; > 99% PIA removal was achieved at an influent concentration of 2.2 mM and a hydraulic retention time of < 10 h. A pure bacterial culture was isolated from a SBR by streaking samples of sludge on solid media with PIA as sole carbon source. The isolate was identified asXanthomonas maltophilia. In liquid culture,X.maltophiliadegraded up to 4.4 mM PIA within 10 days and produced stoichiometric amounts of AMPA. The results demonstrate the biodegradation of PIA and suggest the potential for its treatment in industrial biological treatment systems.Key words: degradation, activated sludge, glyphosate.

ISSN:0008-4166    

DOI:10.1139/m97-014

出版商:NRC Research Press    

年代:1997

数据来源: NRC