Interactions affect hyphal growth and enzyme profiles in combinations of coniferous wood-decaying fungi of Agaricomycetes

Abstract

Fomitopsis pinicola is a species of Polyporales frequently encountered in Nordic temperate and boreal forests. In nature, the fungus causes destructive brown rot in wood, colonizing tree trunks often occupied by other Basidiomycota species. We mimicked these species-species interactions by introducing F. pinicola to five white rot species, all common saprotrophs of Norway spruce. Hyphal interactions and mycelial growth in various combinations were recorded, while activities of lignocellulose-acting CAZymes and oxidoreductases were followed in co-cultures on two different carbon-source media. Of the species, Phlebia radiata and Trichaptum abietinum were the strongest producers of lignin-modifying oxidoreductases (laccase, manganese peroxidase) when evaluated alone, as well as in co-cultures, on the two different growth media (low-nitrogen liquid medium containing ground coniferous wood, and malt extract broth). F. pinicola was an outstanding producer of oxalic acid (up to 61 mM), whereas presence of P. radiata prevented acidification of the growth environment in the liquid malt-extract cultures. When enzyme profiles of the species combinations were clustered, time-dependent changes were observed on wood-supplemented medium during the eight weeks of growth. End-point acidity and production of mycelium, oxalic acid and oxidoreductase activities, in turn clustered the fungal combinations into three distinct functional groups, determined by the presence of F. pinicola and P. radiata, by principal component analysis. Our findings indicate that combinations of wood-decay fungi have dramatic dynamic effects on the production of lignocellulose-active enzymes, which may lead to divergent degradative processes of dead wood and forest litter.

Fig 1. Fungal mycelial interactions recorded after 4, 7 and 17 days of growth on agar media.

Co-cultures of three fungal species, F. pinicola (Fp), P. radiata (Pr), and J. luteoalba (Jl) on (A) malt extract agar, and (B) ABTS agar.

Fig 2

Effect of F. pinicola Fp on laccase activities produced in single-species and co-cultures of P. radiata Pr and Trichaptum abietinum Ta during eight weeks of cultivation on (A) semi-solid wood-supplemented LNAS, and (B) malt extract liquid medium. Mean average values (n = 3, three parallel cultures) with standard deviation are presented at each time point. Fungal abbreviations and combinations, see Table 1 and Table 2.

Fig 3

Effect of F. pinicola Fp on manganese peroxidase (MnP) activities produced by Ta, Pr and Pf, in single-species and co-cultures during eight weeks on (A) semi-solid wood-supplemented LNAS, and (B) malt extract medium. Mean average value (n = 3, three parallel cultures) with standard deviation is presented at each time point. Fungal abbreviations and combinations, see Table 1 and Table 2.

Fig 4

β-glucosidase activities (A) and endo-β-1,4-xylanase activities (B) in single-species and co-cultures during eight weeks on ground wood-supplemented LNAS medium. Species abbreviations and combinations, see Table 1 and Table 2. Mean values of three replicate cultures are presented with standard deviation (error bars).

Fig 5. Principal component analysis including clustering of the CAZyme and oxidoreductase activities (xylanase, xyl; β-glucosidase, bglu; laccase, lac; manganese peroxidase, mnp) of single-species and co-cultures produced at each time point on ground wood-supplemented LNAS medium during eight weeks of cultivation.

Fungal abbreviations and combinations, see Table 1 and Table 2.

Fig 6. Principal component analysis of acidity (poh), concentration of oxalic acid (oa), production of mycelial mass (dry weight, dw), laccase activity (lac) and manganese peroxidase activity (mnp) determined from co-cultures after eight weeks of cultivation on malt extract liquid medium.

Distinct clusters are marked: red circle, Fp single and co-cultures without Pr; orange circle, single-species cultures of Pr and Pf together with co-cultures including Pr—except combination FpPrPf; green circle, white-rot single-species cultures of Ta, Pc, Pf, Jl, and combination FpPrPf. Fungal abbreviations and combinations, see Table 1 and Table 2.