Influence of the enzyme equipment of white-rot fungi on the patterns of wood degradation

Morphological growth pattern of Phanerochaete chrysosporium cultivated on different Miscanthus x giganteus biomass fractions

BACKGROUND

Solid-state fermentation is a fungal culture technique used to produce compounds and products of industrial interest. The growth behaviour of filamentous fungi on solid media is challenging to study due to the intermixity of the substrate and the growing organism. Several strategies are available to measure indirectly the fungal biomass during the fermentation such as following the biochemical production of mycelium-specific components or microscopic observation. The microscopic observation of the development of the mycelium, on lignocellulosic substrate, has not been reported. In this study, we set up an experimental protocol based on microscopy and image processing through which we investigated the growth pattern of Phanerochaete chrysosporium on different Miscanthus x giganteus biomass fractions.

RESULTS

Object coalescence, the occupied surface area, and radial expansion of the colony were measured in time. The substrate was sterilized by autoclaving, which could be considered a type of pre-treatment. The fastest growth rate was measured on the unfractionated biomass, followed by the soluble fraction of the biomass, then the residual solid fractions. The growth rate on the different fractions of the substrate was additive, suggesting that both the solid and soluble fractions were used by the fungus. Based on the FTIR analysis, there were differences in composition between the solid and soluble fractions of the substrate, but the main components for growth were always present. We propose using this novel method for measuring the very initial fungal growth by following the variation of the number of objects over time. Once growth is established, the growth can be followed by measurement of the occupied surface by the mycelium.

CONCLUSION

Our data showed that the growth was affected from the very beginning by the nature of the substrate. The most extensive colonization of the surface was observed with the unfractionated substrate containing both soluble and solid components. The methodology was practical and may be applied to investigate the growth of other fungi, including the influence of environmental parameters on the fungal growth.

Quantification of the CBD-FITC conjugates surface coating on cellulose fibres

Background

Cellulose Binding Domains (CBD) were conjugated with fluorescein isothiocyanate (FITC). The surface concentration of the Binding Domains adsorbed on cellulose fibres was determined by fluorescence image analysis.

Results

For a CBD-FITC concentration of 60 mg/L, a coating fraction of 78% and 110% was estimated for Portucel and Whatman fibres, respectively. For a saturating CBD concentration, using Whatman CF11 fibres, a surface concentration of 25.2 × 10^-13 mol/mm² was estimated, the equivalent to 4 protein monolayers. This result does not imply the existence of several adsorbed protein layers.

Conclusion

It was verified that CBDs were able to penetrate the fibres, according to confocal microscopy and TEM-immunolabelling analysis. The surface concentration of adsorbed CBDs was greater on amorphous fibres (phosphoric acid swollen) than on more crystalline ones (Whatman CF11 and Sigmacell 20).

Ligninolytic characteristics of Pleurotus ostreatus strain F6 and its monokaryotic protoplast derivative P19

A stable isolate of Pleurotus ostreatus P19 differing in some morphological and physiological characteristics from its parental wild-type strain F6 was obtained via protoplast isolation during the preparation of strains with altered ligninolytic abilities. The isolate is monokaryotic, does not form clamp-connections, and produces much higher activities of enzymes involved in lignin modification (laccase, manganese peroxidase). Cellulase activity was comparable to that of wild-type strain F6, but the xylanase activity was slightly higher in isolate P19. However, this monokaryotic derivative degrades lignin at a slightly lower rate than its parental strain F6. Electron microscopy observations of wood degradation as a function of mycelium growth were performed on three zones of birch wafers delimited according to the distance from the point of inoculation. The different stages of fungal mycelium growth showed differences in the ultrastructural patterns of the decay not only between the strains P19 and F6, but also depending on the distance from the point of inoculation. This suggests a spatio-temporally controlled secretion of enzymes along the hyphae. The enhanced ability of P19 to degrade the condensed forms of lignin in middle lamellae is correlated to its higher laccase activity.

Lignin-degrading activity and ligninolytic enzymes of different white-rot fungi: effects of manganese and malonate

Ten species of white-rot fungi, mainly belonging to the family Polyporaceae (Basidiomycotina), were studied in terms of their ability to degrade14C-ring labelled synthetic lignin and secrete ligninolytic enzymes in liquid cultures under varying growth conditions. Lignin mineralization by the fungi in an air atmosphere did not exceed 14% within 29 days. Different responses to the elevated Mn2+concentration and the addition of a manganese chelator (sodium malonate) were observed among various fungal species. This could be related with the utilization of either lignin peroxidase (LiP) or manganese peroxidase (MnP) for lignin depolymerization, i.e., some fungi apparently had an LiP-dominating ligninolytic system and others an MnP-dominating ligninolytic system. The LiP isoforms were purified from Trametes gibbosa and Trametes trogii. Isoelectric focusing of purified ligninolytic enzymes revealed the expression of numerous MnP isoforms in Trametes gibbosa, Trametes hirsuta, Trametes trogii, and Abortiporus biennis grown under a high (50-fold) Mn2+level (120 μM) with the addition of the chelator. In addition, two to three laccase isoforms were detected. Key words: white-rot fungi, lignin degradation, lignin peroxidase, manganese peroxidase, manganese, malonate.