This study investigates the biological activity of bacteria in soil samples collected from sites with summer truffle (Tuber aestivum) (T) ascomata and control sites (C) without T. aestivum at three selected sites (G, M, W) in southern Poland. The number of fragments of the 16S rRNA gene in isolated DNA samples was determined by real−time PCR (qPCR) as a measure of bacterial abundance. Soil metabolic activity was assessed using the BIOLOG system. It was hypothesised that the soil samples studied would differ in terms of the enzymatic and molecular activity of the bacteria inhabiting them. The results obtained for the samples of plots G and W showed differences in bacterial abundance between the two variants. Nevertheless, in plots G and M, the metabolic activity of the microbial communities, as determined by the AWCD index after 100 h of incubation, was higher by ~0.04 and ~0.1 AWCD units, respectively, in the control variant than in the soil samples with T. aestivum. This implies that studies of bacterial communities in soil should consider both copy gene numbers and community activity as measured by the AWCD index. The results of this study deepen the knowledge about the bacterial communities and their metabolic activity in soils with T. aestivum and their potential influence on the formation of T. aestivum ascomata., Sylwan 166 (1): 54-70