Microbial diversity in rhizosphere and bulk soil

Soil microbes are of enormous importance for functioning nutrient cycles as well as for plant health. The development and application of nucleic acid based techniques provided new insights into the diversity of bulk and rhizosphere soil microbes. The microbial diversity in soils was shown by means of cultivation-independent methods to be influenced by various biotic and abiotic factors. Sequence based analysis of 16S rRNA genes and ITS fragments amplified from total DNA extracted directly from soil allows to determine the taxonomic affiliation (phylum, class, order, genera and species) of those taxa influenced in their relative abundance by the plant species or genotype, the site, or changes in agricultural management. The diversification within a species and the adaptation of bacterial populations to changing environmental conditions is often fostered by mobile genetic elements. Pathogenicity determinants, genes responsible for the bacterial interaction with its host plant or antibiotic and heavy metal resistance genes are often localized on plasmids. This review summarizes research on microbial diversity performed over more than twenty years at the BBA and now in the JKI in Braunschweig.