Molecular diversity in the bacterial communities and the fluorescent pseudomonads group in natural and chlorobenzoate-stressed peat-forest soil

The bacterial community shifts in a peat forest soil microcosms spiked with 3-chlorobenzoate (3CBA) or 2,5-dichlorobenzoate (2,5DCB) were monitored. The 16S rRNA was used as a molecular marker in combination with the temperature gradient gel electrophoresis (TGGE) profiling technique. Shannon´s diversity and equitability indices were used as parameters of community changes for both, a selected cultivable fraction of fluorescent pseudomonads and the uncultured total bacterial community. Addition of the chlorinated benzoates to soil suppressed in 10 - 100 fold the overall growth of aerobic bacteria as evaluated by plate counting in a glucose-containing medium. However, this addition had no effect on the diversity within the group of fluorescent pseudomonads as assessed by differential isolation and a fast TGGE-based typing technique. In contrast, the uncultured bacterial community showed a decrease in the number of bands in the TGGE profiles of the chlorobenzoate-spiked treatments. Accordingly, the diversity and equitability indices of these treatments reflected a decreasing trend in time. The indices were calculated from the relative band intensities of the TGGE profiles accomplished by image analysis. The results indicate that chlorobenzoates have a marked effect on the soil bacterial community. The approach allowed direct analysis of complex bacterial communities, being a rapid method to assess community shifts upon contamination of the environment with toxic compounds.