de Boer, W. | bioRxiv Science

bioRxiv2020

Effect of nitrogen on fungal growth efficiency

The contribution of fungi to carbon (C) and nitrogen (N) cycling is related to their growth efficiency (amount of biomass produced per unit of substrate utilized). The concentration and availability of N influences the activity and growth efficiency of saprotrophic fungi. When N is scarce in soils, fungi have to invest more energy to obtain soil N, which could result in lower growth efficiencies. Yet, the effect of N on growth efficiencies of individual species of fungi in soil has not been studied extensively. In this study we investigated the influence of different concentrations of mineral N on the growth efficiency of two common soil fungi, Trichoderma harzanium and Mucor hiemalis in a soil-like environment. We hypothesized that a higher N availability will coincide with higher biomass production and growth efficiency. To test this, we measured fungal biomass production as well as the respiration fluxes in sand microcosms amended with cellobiose and mineral N at different C:N ratios. We found that for both fungal species lower C:N ratios resulted in the highest biomass production as well as the highest growth efficiency. This may imply that when N is applied concurrently with a degradable C source, a higher amount of N will be temporarily immobilized into fungal biomass.

ecology↗

bioRxiv2020

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.

microbiology↗