Decomposition of spruce wood and release of volatile organic compounds depend on decay type, fungal interactions and enzyme production patterns

Abstract

Effect of three wood-decaying fungi on decomposition of spruce wood was studied in solid-state cultivation conditions for a period of three months. Two white rot species (Trichaptum abietinum and Phlebia radiata) were challenged by a brown rot species (Fomitopsis pinicola) in varying combinations. Wood decomposition patterns as determined by mass loss, carbon to nitrogen ratio, accumulation of dissolved sugars and release of volatile organic compounds (VOCs) were observed to depend on both fungal combinations and growth time. Similar dependence of fungal species combination, either white or brown rot dominated, was observed for secreted enzyme activities on spruce wood. Fenton chemistry suggesting reduction of Fe3+ to Fe2+ was detected in the presence of F. pinicola, even in co-cultures, together with substantial degradation of wood carbohydrates and accumulation of oxalic acid. Significant correlation was perceived with two enzyme activity patterns (oxidoreductases produced by white rot fungi; hydrolytic enzymes produced by the brown rot fungus) and wood degradation efficiency. Moreover, emission of four signature VOCs clearly grouped the fungal combinations. Our results indicate that fungal decay type, either brown or white rot, determines the loss of wood mass and decomposition of polysaccharides as well as the pattern of VOCs released upon fungal growth on spruce wood.

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

“…Even though three putative genes for laccase have been annotated in the genome of F. pinicola [4,10], no extracellular laccase activity was observed on birch wood with the fungus. A similar absence of laccase activity was observed in our previous study adopting the same isolate, both on semi-solid liquid cultures and solid-state cultures on coniferous wood [17,22,27]. These observations indicate that the presence of certain genes is not necessarily an indication of fungal expression of the enzyme and production of extracellular activity on natural, solid lignocellulose substrates.…”

“…This effect may also be a consequence of more preferred growth on birch wood since the species has specificity of inhabitation and decomposition of dead deciduous wood in nature [28]. P. radiata also produced the highest MnP activities, and likewise observed previously on spruce wood, MnP production was occurring simultaneously with laccase activity [12,27,28]. On the carbohydrate-rich liquid ME medium, low laccase but distinct MnP activities were produced by P. radiata, demonstrating the stability of lignin-attacking oxidoreductase expression in the early phase of growth and decomposition processes.…”

“…These observations confirm that the fungus is a strong producer of laccase on solid wood lignocellulose substrates. However, a higher level of laccase activity was now observed on birch wood than previously attained on coniferous wood [12,22,24,27], suggesting potential promotion of laccase production by the lignocellulose substrate. This effect may also be a consequence of more preferred growth on birch wood since the species has specificity of inhabitation and decomposition of dead deciduous wood in nature [28].…”

“…Therefore, it was expected that the production of β-glucosidase activity by P. radiata would remain low during cultivations on birch wood, at the levels lower than 1 nkat mL −1 as was observed previously on spruce wood [24,27,28]. Regarding endoglucanase production, the enzyme activity profile was difficult to interpret due to interference in the assay method of a considerable accumulation of sugars released into the solution by fungal enzymatic activity, breaking wood cellulose and hemicelluloses into sugars [25,27]. However, some endoglucanase net activity could be observed after the third week on birch wood cultures of P. radiata, just after the peak of laccase and MnP activities.…”

“…White rot fungi are able to modify lignin and decompose wood cell wall polysaccharides leaving most of cellulose as a white residue [1][2][3][4][5]. Therefore, it was expected that the production of β-glucosidase activity by P. radiata would remain low during cultivations on birch wood, at the levels lower than 1 nkat mL −1 as was observed previously on spruce wood [24,27,28]. Regarding endoglucanase production, the enzyme activity profile was difficult to interpret due to interference in the assay method of a considerable accumulation of sugars released into the solution by fungal enzymatic activity, breaking wood cellulose and hemicelluloses into sugars [25,27].…”