Conclusions. Community analysis by T-RFLP of 16S rRNA
genes proved to be a highly suitable and sensitive tool with
which to investigate the microbial community structures in
different particle size fractions and treatments. Three normalized
replicate samples of each fraction and treatment showed
comparable population profiles and grouped well in a cluster
analysis. Quantitative T-RFLP analysis has to be treated with
caution due to biases inherent to PCR amplification (53) and
variations in the copy number of the 16S rRNA gene in different
bacterial species (8). However, with awareness of these
limitations, T-RFLP analysis can be used for a semiquantitative
analysis of bacterial community structures (12, 47). In this
experiment, the microbial composition was mainly affected by
the particle size fraction and did respond to a lesser extent to
organic amendments. Therefore, our results demonstrate specific
microbe-particle associations that are affected to a smaller
extent by external factors such as fertilization or heavy metal
pollution (32). Knowledge of the microbial community structure
represents a first step toward understanding soil function
in response to the environment. In addition to community
structure, the analysis of functional genes within a given population
will greatly increase our comprehension of the role of
bacteria in soil processes important for geochemical dynamics
of elements, specifically carbon, nitrogen, and sulfur.