Humic substances enhance growth and respiration in the basidiomycetes Trametes maxima under carbon limited conditions.

Humic substances (HS) represent the major reservoir of carbon (C) in ecosystems, and their turnover is crucial for understanding the global C cycle. Although basidiomycetes clearly have a role in HS degradation, much less is known about the effect of HS on fungal traits. We studied the alteration of physiological, biochemical, and morphological characteristics of Trametes maxima in the presence of HS. Both complete medium and minimal (C-limited) medium mimicking natural environmental conditions were used. Adding HS led to increased biomass yield, but under C-limited conditions the effect was more apparent. This result indicated that HS were used as an additional substrate and agreed with data showing a greater penetration of tritium-labeled HS into the cell interior under C-limited conditions. Humic substances induced ultra-structural changes in fungal cells, especially under C limitation, including reducing the thicknesses of the hyphal sheath and cell wall. In the minimal medium, cellular respiration increased nearly three-fold under HS application, while the corresponding effect in complete medium was lower. In addition, in the presence of inhibitors, HS stimulated either the cytochrome or the alternative pathway of respiration, depending on presence or absence of glucose in the medium. Our results suggest that, under conditions mimicking the natural environment, HS may play three major roles: as a surplus substrate for fungal growth, as a factor positively affecting cell morphology, and as an activator of physiological respiration.

Coarsening of extracellularly biosynthesized cadmium crystal particles induced by thioacetamide in solution.

A novel coarsening route for extracellularly biosynthesized cadmium nanocrystals was investigated for the first time. In this process, the white rot fungus Coriolus versicolor was employed to take up cadmium ions and synthesize extracellular cadmium crystal particles. The coarsening of the particles was induced by thioacetamide under certain conditions. Scanning electron microscopy showed that the formed cadmium crystal particles were coarsened from about 100nm to 2-3µm. The corresponding energy-dispersive X-ray spectra confirmed the presence of proteins in the particles. The maximum removal efficiency of Cd(II) increased from 17% to 87%, and the corresponding sorption capacity of biomass increased from 4 to 24mgg(-1) with the completion of the coarsening process. The properties of the coarsened particles were also examined using X-ray diffraction (XRD) and transmission electron microscopy (TEM). XRD analysis of fungal mycelial pellets embedded with the coarsened particles confirmed the formation of cubic crystalline cadmium sulfide particles. The TEM results suggest that the coarsened particles were composed of clusters of several smaller particles. The changes in the functional groups on the biomass surface were studied through Fourier transform infrared spectroscopy. Based on the results above, a possible mechanism for the formation and coarsening of cadmium crystal particle is also discussed.

Investigation of growth responses in saprophytic fungi to charred biomass.

We present the results of a study testing the response of two saprophytic white-rot fungi species, Pleurotus pulmonarius and Coriolus versicolor, to charred biomass (charcoal) as a growth substrate. We used a combination of optical microscopy, scanning electron microscopy, elemental abundance measurements, and isotope ratio mass spectrometry ((13)C and (15)N) to investigate fungal colonisation of control and incubated samples of Scots Pine (Pinus sylvestris) wood, and charcoal from the same species produced at 300 degrees C and 400 degrees C. Both species of fungi colonise the surface and interior of wood and charcoals over time periods of less than 70 days; however, distinctly different growth forms are evident between the exterior and interior of the charcoal substrate, with hyphal penetration concentrated along lines of structural weakness. Although the fungi were able to degrade and metabolise the pine wood, charcoal does not form a readily available source of fungal nutrients at least for these species under the conditions used in this study.

Three-dimensional x-ray imaging and analysis of fungi on and in wood.

As wood is prone to fungal degradation, fundamental research is necessary to increase our knowledge aiming at product improvement. Several imaging modalities are capable of visualizing fungi, but the X-ray equipment presented in this article can envisage fungal mycelium in wood nondestructively in three dimensions with submicron resolution. Four types of wood subjected to the action of the white rot fungus Coriolus versicolor (Linnaeus) Quélet (CTB 863 A) were scanned using an X-ray-based approach. Comparison of wood volumes before and after fungal exposure, segmented manually or semiautomatically, showed the presence of the fungal mass on and in the wood samples and therefore demonstrated the usefulness of computed X-ray tomography for mycological and wood research. Further improvements to the experimental setup are necessary to resolve individual hyphae and enhance segmentation.