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- 2011 (2) (entfernen)
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- Basidiomycetes (1)
- Fungi (1)
- IRMS (1)
- Isotope labeling (1)
- Microbial interaction (1)
- N2 assimilation (1)
- Nitrogen (1)
- S K-edge X-ray absorption near edge spectroscopy (XANES) (1)
- Sulfate-esters (1)
- Sulfur oxidation status (1)
The main wood degraders in aerobic terrestrial ecosystems belong to the white- and brown-rot fungi, where their biomass can be created on wood decay only. However, total sulfur (S) concentration in wood is very low and only little is known about the different sulfur compounds in wood today. Sulfur-starved brown-rot fungi Gloeophyllum trabeum and Oligoporus placenta were incubated on sterilized pine wood blocks whereas Lentinus cyathiformis and the white-rot fungi Trametes versicolor were incubated on sterilized beech wood blocks. After 19 weeks of incubation, the S oxidation status was analyzed in wood, in degraded wood, and in biomass of wood-degrading fungi by synchrotron based S K-edge XANES, and total S and sulfate were quantified. Total sulfur and sulfate content in pine wood blocks were approximately 50 and 1 µg g-1, respectively, while in beech wood approximately 100 and 20 µg g-1 were found, respectively. Sulfur in beech was dominated by sulfate-esters. In contrast, pine wood also contained larger amounts of reduced S. Three out of four selected fungi caused a reduction of the S oxidation state in wood from oxidized S (sulfate-ester, sulfate) to intermediate S (sulfonate, sulfoxide) or reduced S (thiols, e.g., proteins, peptides, enzyme cofactors). Only O. placenta shifted thiol to sulfonate. Growth experiments of these fungi on selective minimal media showed that in particular cysteine (thiol), sulfonates, and sulfate enhanced total mycelium growth. Consequently, wood-degrading fungi were able to utilize a large variety of different wood S sources for growth but preferentially transformed in vivo sulfate-esters and thiol into biomass structures.
Isotope ratio mass spectrometry (IRMS) is an advanced method to investigate carbon (C) and nitrogen (N) in organic samples. In particular, the N content, its isotope signature and the C/N ratio reveal important facts of nutrient cycling, niche separation and ecological food webs. In this study, the characteristics of N turnover of wood decomposing microorganisms were investigated.
The growth of the white rot causing basidiomycete Trametes versicolor is enhanced after addition of ammonia or urea, whereas the brown rot causing Oligoporus placenta is not accelerated. In addition, an interaction of each fungus with atmospheric N2 assimilating (diazotrophic) bacteria was investigated. Cultivation experiments with a gas mixture of 15N2/O2 and subsequent IRMS analysis of dry biomass of the diazotrophs Azotobacter croococcum, Beijerinckia acida and Novosphingobium nitrogenifigens revealed that they assimilated up to 12% of their N from N2. The experiments reflected N availability as a prerequisite for efficient growth of decomposing basidiomycetes and diazotrophs. Fungal–bacterial co-cultivation experiments showed that depending on the growth characteristics and bacterial N2 assimilation activity N is transferred from certain bacteria into fungal biomass. Thus, the experiments gave a first indication of an interaction between wood decomposing basidiomycetes and diazotrophs, which is a novel pathway of fungal N acquisition.