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  • 1
    Electronic Resource
    Electronic Resource
    Effect of long-term herbicide applications on the bacterial community structure and function in an agricultural soil (2003)
    Oxford, UK : Blackwell Publishing Ltd
    FEMS microbiology ecology 46 (2003), S. 0 
    Details
    ISSN: 1574-6941
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Little is known about the chronic effect of herbicides on the soil microbial community, with most studies focusing on acute impacts. In this study, we investigated the effect of 20 years of atrazine and metolachlor application on the community structure, abundance and function of bacterial groups in the bulk soil of a maize monoculture. Group-specific PCR-DGGE (polymerase chain reaction-denaturing gradient gel electrophoresis) of 16S rRNA genes was used to characterize the composition of the microbial community. Primers specific for the entire bacterial group, as well as for the Acidobacterium group, the actinomycetes, the ammonium oxidizers, and the Type I and II methanotrophs were used in the PCR-DGGE analysis. Cluster analysis of the DGGE patterns obtained with the different primer sets differentiated between the herbicide-treated and the non-treated control soil. In particular the methanotrophic community differed, with three bands (phylotypes) being absent (or showing a lower intensity) in the DGGE patterns of the herbicide-treated soils compared to the patterns of the control soil. The differences in the methanotrophic community structure were not reflected in the methane oxidation capacity, which was similar for the two treatments. The prevalence of methanotrophs as evaluated with real-time PCR analysis also did not differ between the herbicide-treated and non-treated soil. Our results indicate that the long-term use of the herbicides atrazine and metolachlor resulted in an altered soil community structure, in particular for the methanotrophic bacteria. These observed changes did not cause a decreased community function (methane oxidation), probably because the total abundance of the methanotrophs in the soil system was preserved.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1016/S0168-6496(03)00205-8
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  • 2
    Electronic Resource
    Electronic Resource
    Diversity of root-associated bacteria associated with field-grown canola (Brassica napus L.) and wheat (Triticum aestivum L.) (1998)
    Oxford, UK : Blackwell Publishing Ltd
    FEMS microbiology ecology 26 (1998), S. 0 
    Details
    ISSN: 1574-6941
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Little is known about the composition and diversity of the bacterial community associated with plant roots. The purpose of this study was to investigate the diversity of bacteria associated with the roots of canola plants grown at three field locations in Saskatchewan, Canada. Over 300 rhizoplane and 220 endophytic bacteria were randomly selected from agar-solidified trypticase soy broth, and identified using fatty acid methyl ester (FAME) profiles. Based on FAME profiles, 18 bacterial genera were identified with a similarity index 〉0.3, but 73% of the identified isolates belonged to four genera: Bacillus (29%), Flavobacterium (12%), Micrococcus (20%) and Rathayibacter (12%). The endophytic community had a lower Shannon-Weaver diversity index (1.35) compared to the rhizoplane (2.15), and a higher proportion of Bacillus, Flavobacterium, Micrococcus and Rathayibacter genera compared to rhizoplane populations. Genera identified in the endophytic isolates were also found in the rhizoplane isolates. Furthermore, principal component analysis indicated three clusters of bacteria regardless of their site of origin, i.e., rhizoplane or endophytic. In addition, the rhizoplane communities of canola and wheat grown at the same site differed significantly. These results indicate that diverse groups of bacteria are associated with field-grown plants and that endophytes are a subset of the rhizoplane community.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1574-6941.1998.tb01560.x
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  • 3
    Electronic Resource
    Electronic Resource
    Reduction in denitrification activity in field soils exposed to long term contamination by 2,4,6-trinitrotoluene (TNT) (2000)
    Oxford, UK : Blackwell Publishing Ltd
    FEMS microbiology ecology 32 (2000), S. 0 
    Details
    ISSN: 1574-6941
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Terrestrial sites contaminated with 2,4,6-trinitrotoluene (TNT) are a widespread and persistent problem and often contain non-vegetated areas with TNT concentrations well in excess of 1000 mg kg−1. In this study, we examined the effect of TNT on denitrification activity in field soils, and compared the sensitivity of denitrifying enzymes to TNT. DNA probes assessed the prevalence of nirS, nirK and nosZ (encoding cd1 or copper nitrite reductase and nitrous oxide reductase, respectively), denitrifying genotypes in the culturable and total microbial community. The nitrate (NaR), nitrite (NiR) and nitrous oxide (N2OR) reductase activities in field soil and in isolates were assessed by gas chromatography. The relative occurrence of the nirK, nirS or nosZ genotypes increased in the cultured community and in total uncultured community DNA as nitroaromatic concentrations increased. However, denitrifying activity decreased in response to increasing TNT concentrations, with an IC50 for NaR+NiR+nitric oxide reductase (NOR) of 400 mg TNT kg−1 soil and for N2OR of 26 mg TNT kg−1 soil. The denitrifying activity of four soil isolates also decreased in response to TNT, with N2OR activity being three times more sensitive to TNT than NaR+NiR+NOR activity. Interestingly, there were 118 times more nirK isolates than nirS isolates in uncontaminated soil but only 1.5 times more in soil containing 17 400 mg kg−1 TNT. The results from this study indicated that TNT reduced denitrification activity in field soils, and N2OR was much more sensitive to TNT than NaR+NiR+NOR.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1574-6941.2000.tb00699.x
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    Paper (German National Licenses)
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  • 4
    Electronic Resource
    Electronic Resource
    Phenotypic plasticity of Pseudomonas aureofaciens (lacZY) introduced into and recovered from field and laboratory microcosm soils (1998)
    Oxford, UK : Blackwell Publishing Ltd
    FEMS microbiology ecology 27 (1998), S. 0 
    Details
    ISSN: 1574-6941
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: The ability of bacteria to alter phenotypic characteristics during their survival and persistence in soil complicates the risk assessment of bacterial inoculants, especially those genetically engineered. The purpose of this study was to investigate changes in the phenotype of Pseudomonas aureofaciens 3732 RN-L11 (lacZY) introduced into and recovered from wheat roots or soil obtained from the field or laboratory microcosms. Fatty acid methyl ester (FAME) and Biolog™ analyses were used to characterize the phenotype of 88 isolates obtained from soil collected over a 2-year period. There was variation in the relative proportions of fatty acids found in isolates over the growing season, with FAME profiles of isolates obtained at 14, 28 and 70 days after planting different from isolates obtained at day 0 and day 140. However, these changes were not sufficient to alter the species designation. Similarly, carbon substrate utilization by isolates varied only slightly over the growing season. In addition, there were few phenotypic differences found between isolates obtained from rhizosphere or bulk soil, and no observed differences between isolates recovered from field soil or microcosms. Our results indicate that there was little phenotypic drift of this genetically engineered bacterium during its survival in field and laboratory microcosm soils.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1574-6941.1998.tb00531.x
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    Paper (German National Licenses)
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