No abstract

The bacterial community composition in soil and rhizosphere taken from arable field sites, differing in soil parent material and soil texture, was analyzed using terminal restriction fragment length polymorphism (T-RFLP) of 16S rRNA genes. Nine sandy to silty soils from North-East Germany could clearly be distinguished from each other, with a relatively low heterogeneity in the community structure within the field replicates. There was a relationship between the soil parent material, i.e. different glacial and aeolian sediments, and the clustering of the profiles from different sites. A site-specific grouping of T-RFLP profiles was also found for the rhizosphere samples of the same field sites that were planted with potatoes. The branching of the rhizosphere profiles corresponded partly with the soil parent material, whereas the effect of the plant genotype was negligible. Selected terminal restriction fragments differing in their relative abundance within the nine soils were analyzed based on the cloning of the 16S rRNA genes of one soil sample. A high phylogenetic diversity observed to include Acidobacteria, Betaproteobacteria, Bacteroidetes, Verrucomicrobia, and Gemmatimonadetes. The assignment of three out of the seven selected terminal restriction fragments to members of Acidobacteria suggested that this group seems to participate frequently in the shifting of community structures that result from soil property changes.

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No abstract

The rhizosphere and phyllosphere microbial communities of transgenic potatoes producing fructan were studied in comparison with isogenic controls and conventional varieties in a field release experiment over a period of 3 years. Population densities and 16S rRNA gene-based terminal restriction fragment length polymorphism (T-RFLP) analysis of the rhizosphere bacterial community only displayed the influence of annual and seasonal effects and the influence of field heterogeneity. In contrast, the T-RFLP analysis of the phyllosphere bacteria revealed in two of the 3 years significant differences in the community structure between the transgenic lines producing inulin and the other variants. This effect was studied in more detail through the analysis of bacterial isolates and a 16S rRNA gene clone library obtained from a transgenic line and the control. Both methods revealed a lower genetic diversity in the transgenic line and changes in the abundance of several bacterial groups. The isolates of the transgenic line were dominated by Bacilli, whereas most of the control isolates represented Actinobacteria. The clones were dominated by Proteobacteria, with main differences between both variants in Deltaproteobacteria, Bacilli and Bacteroidetes. However, all in all, the impact of the transgenic lines did not exceed the natural variability of the phyllosphere community structure on potato plants.