Estimation of the Effects of Earthworms and Initial Substrates on the Bacterial Community in Vermicomposts

The effects of earthworms and initial substrates on the structural and functional compositions of the bacterial community in vermicomposts have been estimated by the method of denaturing gradient gel electrophoresis (DGGE) of amplified bacterial 16S rRNA gene fragments and by the kinetic method for assessing the physiological state of bacterial communities. ANOVA of the data on structural characteristics of the community (DGGE data) has demonstrated that the nature of the composted substrate has the major effect on the structure of the bacterial community. The associated variance for this factor accounts for 53% and exceeds the effect of earthworms (29%). A functional characterization of the bacterial community (data on the physiological state of bacteria as judged from their growth on different organic compounds) suggests that the presence of earthworms activates the bacterial community by increasing the variable characterizing the physiological state of bacteria (r(0)). As has been shown, it is impossible to predict the effect of earthworms on the particular bacterial taxa, because the effects of similar signs (increase, decrease, or the absence of changes in all the variants) just for the three analyzed types of substrates have only been observed for 15% of the operational taxonomic units.