Identification and antimicrobial properties of bacteria isolated from naturally decaying wood

Research on wood decay in forest ecosystems has traditionally focused on wood-rot fungi, which lead the decay process through attack of the lignocellulose complex. The role of bacteria, which can be highly abundant, is still unclear. Wood-inhabiting bacteria are thought to be nutritionally dependent on decay activities of wood-rot fungi. Therefore, we hypothesized that these bacteria are not antagonistic against wood-rot fungi whereas antagonistic activity against other bacteria may be high (resource competition). This was examined for decaying wood in temperate forests. We found that the abundance of cultivable bacteria in decaying wood can be highly variable. The general pattern is an increase of bacteria with progressive decay, but we also identified several fungi that were apparently able to exclude bacteria from their woody territory. We established a bacterial collection which is highly representative for decaying wood with typical wood-inhabiting taxa: Xanthomonadaceae, Acetobacteraceae, Caulobacteraceae, Methylovirgula, Sphingomonas, Burkholderia and Granulicella. In vitro antagonistic activity against other bacteria and fungi was evaluated. In contrast to our hypothesis, we found surprisingly low antagonistic activity against bacteria (<2% of isolates), while antagonism against fungi was more prevalent. These results may point at a prominent role of mycophagy (growth at the expense of living fungi) among wood-inhabiting bacteria.