Enzyme Activity Profiles Produced on Wood and Straw by Four Fungi of Different Decay Strategies

Abstract

Four well-studied saprotrophic Basidiomycota Agaricomycetes species with different decay strategies were cultivated on solid lignocellulose substrates to compare their extracellular decomposing carbohydrate-active and lignin-attacking enzyme production profiles. Two Polyporales species, the white rot fungus Phlebia radiata and brown rot fungus Fomitopsis pinicola, as well as one Agaricales species, the intermediate "grey" rot fungus Schizophyllum commune, were cultivated on birch wood pieces for 12 weeks, whereas the second Agaricales species, the litter-decomposing fungus Coprinopsis cinerea was cultivated on barley straw for 6 weeks under laboratory conditions. During 3 months of growth on birch wood, only the white rot fungus P. radiata produced high laccase and MnP activities. The brown rot fungus F. pinicola demonstrated notable production of xylanase activity up to 43 nkat/mL on birch wood, together with moderate β-glucosidase and endoglucanase cellulolytic activities. The intermediate rot fungus S. commune was the strongest producer of β-glucosidase with activities up to 54 nkat/mL, and a notable producer of xylanase activity, even up to 620 nkat/mL, on birch wood. Low lignin-attacking but moderate activities against cellulose and hemicellulose were observed with the litter-decomposer C. cinerea on barley straw. Overall, our results imply that plant cell wall decomposition ability of taxonomically and ecologically divergent fungi is in line with their enzymatic decay strategy, which is fundamental in understanding their physiology and potential for biotechnological applications.

Keywords: Basidiomycota; biodegradation; carbohydrate active enzymes; enzyme activity assays; laccase; lignocellulose; manganese peroxidase; organic acids; oxalic acid; wood decay fungi.

Figure 1

Laccase activities produced by (a) the WR fungus P. radiata; (b) the BR fungus F. pinicola; (c) the GR fungus S. commune; and (d) the LDF species C. cinerea. Fungal cultivations on birch wood (blue line with spheres), on barley straw (black line with spheres) and on liquid ME medium (orange line with spheres). Values from control incubations of birch wood (blue triangles), barley straw (black triangles) and liquid ME medium (orange triangles) without fungi are included. Mean value (n = 3) is presented at each week time point. Bars indicate the standard error. * statistically significant changes between time points. Notice different scales in the y axis. For information on the fungi, see Table 1.

Figure 2

Manganese peroxidase (MnP) activities produced by (a) the WR fungus P. radiata; (b) the GR fungus S. commune; and (c) the LDF species C. cinerea. Fungal cultivations on birch wood (blue line with spheres), barley straw (black line with spheres) and liquid ME medium (orange line with spheres). Values from control incubations of birch wood (blue triangles), barley straw (black triangles) and liquid ME medium (orange triangles) without fungi are included. Mean value (n = 3) is presented at each week time point. Bars indicate the standard error. * statistically significant value between the time points. For information on the fungi, see Table 1.

Figure 3

β-glucosidase activities produced by (a) the WR fungus P. radiata; (b) the BR fungus F. pinicola; (c) the GR fungus S. commune; and (d) the LDF species C. cinerea. Fungal cultivations on birch wood (blue line with spheres), on barley straw (black line with spheres) and on liquid ME medium (orange line with spheres). Values from control incubations of birch wood (blue triangles), barley straw (black triangles) and liquid ME medium (orange triangles) without fungi are included. Mean value (n = 3) is presented at each week time point. Bars indicate the standard error. * statistically significant changes between time points. Notice different scales in the y axis. For information on the fungi, see Table 1.

Figure 4

Endoglucanase activities produced by (a) the WR fungus P. radiata; (b) the BR fungus F. pinicola; (c) the GR fungus S. commune; and (d) the LDF species C. cinerea. Fungal cultivations on birch wood (blue line with spheres) and on barley straw (black line with spheres). Values from control incubations of birch wood (blue triangles) and barley straw (black triangles) without fungi are included. Net activity values are also shown (green dotted lines) after subtracting the control activity. Mean value (n = 3) is presented at each week time point. Bars indicate the standard error. Notice different scales in the y axis. For information on the fungi, see Table 1.

Figure 5

Xylanase activities produced by (a) the WR fungus P. radiata; (b) the BR fungus F. pinicola; (c) the GR fungus S. commune; and (d) the LDF species C. cinerea. Fungal cultivations on birch wood (blue line with spheres) and on barley straw (black line with spheres). Values from control incubations of birch wood (blue triangles) and barley straw (black triangles) without fungi are included. (a,d) Net activity values are also shown (green dotted lines) after subtracting the control activity. Mean value (n = 3) is presented at each week time point. Bars indicate the standard error. Notice different scales in the y axis. *, + statistically significant changes between time points. For information on the fungi, see Table 1.

Figure 6

pH values recorded during 12 weeks of lignocellulose solid-state cultivations and 4 weeks on ME liquid medium, cultures of (a) WR fungus P. radiata; (b) BR fungus F. pinicola; (c) “GR” fungus S. commune; (d) LDF C. cinerea. Fungal cultivations were performed on birch wood (blue line with spheres) or barley straw (black line with spheres), and on liquid ME medium (orange line with spheres). Values from control incubations of birch wood (blue triangles, dotted line), barley straw (black triangles, dotted line) and liquid ME medium (orange triangles, dotted line) without fungi are included. Mean value (n = 3) is presented at each week time point. Bars indicate the standard error.

Figure 7

Accumulation of organic acids in the fungal solid-state cultures on lignocellulose substrates at weekly time points. Organic acids were measured by HPLC analysis of culture fluid samples. W1–W12; cultivation week 1–12. Concentration of fumaric acid in the cultures of C. cinerea on barley straw was lower than the detection limit (<0.5 mM) and thereby invisible in the figure. Mean value (n = 3) is presented at each week time point. Bars indicate the standard error. n.d., not detected; WR, white rot; BR, brown rot; GR, grey rot, intermediate decay type; LDF, litter-decomposing fungus.