Interactions of Bacteria and Fungi on Decomposing Litter: Differential Extracellular Enzyme Activities

Abstract

Fungi and bacteria are key agents in plant litter decomposition in freshwater ecosystems. However, the specific roles of these two groups and their interactions during the decomposition process are unclear. We compared the growth and patterns of degradative enzymes expressed by communities of bacteria and fungi grown separately and in coexistence on Phragmites leaves. The two groups displayed both synergistic and antagonistic interactions. Bacteria grew better together with fungi than alone. In addition, there was a negative effect of bacteria on fungi, which appeared to be caused by suppression of fungal growth and biomass accrual rather than specifically affecting enzyme activity. Fungi growing alone had a high capacity for the decomposition of plant polymers such as lignin, cellulose, and hemicellulose. In contrast, enzyme activities were in general low when bacteria grew alone, and the activity of key enzymes in the degradation of lignin and cellulose (phenol oxidase and cellobiohydrolase) was undetectable in the bacteria-only treatment. Still, biomass-specific activities of most enzymes were higher in bacteria than in fungi. The low total activity and growth of bacteria in the absence of fungi in spite of apparent high enzymatic efficiency during the degradation of many substrates suggest that fungi provide the bacteria with resources that the bacteria were not able to acquire on their own, most probably intermediate decomposition products released by fungi that could be used by bacteria.

Contribution of soil respiration to the global carbon equation

“…The two main groups of these decomposers are bacteria and fungi, and they are involved in both aerobic and anaerobic degradation of organic matter. These microbes produce extracellular enzymes to convert polymeric compounds, such as cellulose, hemicellulose, and lignin, in the SOM into smaller molecules that can be further assimilated inside the microbial cells (Romaní et al, 2006). Fungi are more efficient than bacteria in the degradation of highly recalcitrant organic matter because they can produce a wider range of extracellular enzymes than bacteria (Szafranek-Nakonieczna and Stêpniewska, 2014).…”

Initial decay of woody fragments in soil is influenced by size, vertical position, nitrogen availability and soil origin

“…Hence, for the abandoned arable soil a better fungal growth in woodblocks as compared to sawdust may be caused by a lower competitive pressure of bacteria. A negative effect of bacteria on fungal growth has been suggested to be due to bacterial release of lytic enzymes degrading fungal cell walls, to the production of antifungal compounds (antibiotics) or to the competition for available organic compounds between bacteria and fungi (De Boer et al 2003;Romani et al 2006). Since there is a lower decomposition rate in sawdust as compared to woodblocks, we assume that there are negative effects (antagonism) of bacteria on fungi and vice versa resulting in a net lower decomposition.…”

The role of organisms in hyporheic processes: gaps in current knowledge, needs for future research and applications

“…Microbial communities (Table 3) A large number of studies that describe microbial dynamics in the sediment have been supported by potential activities measured in the laboratory, for organic matter degradation (Sinsabaugh et al, 1993;Romani et al, 2006) or nitrogen cycling (Pinay and De´camps, 1988;Clement et al, 2002;Sabater et al, 2003;Lefebvre et al, 2005). There is likely a substantial gap between these experimental activities and the intensity of the processes that take place in situ (Pinay and De´camps, 1988;Sa´nchez-Pe´rez et al, 2003a, b;Iribar et al, 2008).…”