Effects of tylosin as a disturbance on the soil microbial community

The effect of a strong temporary disturbance on the soil microbial community was investigated and the ability of the community to show resilience with respect to bacterial diversity and structure was examined. Soil was treated with the antibiotic tylosin and incubated for 2 months. After 3 weeks, the added tylosin and its degradation products had disappeared. During incubation, the populations of bacteria, fungi and protozoa in the soil responded to the tylosin treatment; the changes in the population sizes being strongest the first 2 weeks after treatment, after which it diminished. The diversity (number and abundance) of colony morphotypes decreased temporarily following the disturbance whereas a more permanent change in diversity was revealed investigating amplified 16S rDNA sequences from total community DNA by DGGE. The community structure (PCA) based on both colony morphology, DGGE and sole carbon source utilisation obtained by Ecoplates® was altered due to the tylosin treatment throughout the experiment. The DGGE was the most sensitive method. Differences in diversity and community structure found by this method were maintained for 2 months. However, the results were highly dependent on the DNA-extraction procedure. e shown that diversity as a composite community parameter can attain its original value following the disturbance, whereas changes in community structure were permanent. It is therefore important to focus on community structure and not only on diversity, when evaluating the effect of disturbances on soil populations in relation to system functioning.