Enzymatic Bioweathering and Metal Mobilization From Black Slate by the Basidiomycete Schizophyllum commune

Abstract

Schizophyllum commune is a filamentous basidiomycete causing white-rot in many wood species with the help of a broad range of enzymes including multicopper oxidases such as laccases and laccase-like oxidases. Since these enzymes exhibit a broad substrate range, their ability to oxidatively degrade black slate was investigated. Both haploid monokaryotic, and mated dikaryotic strains were able to grow on black slate rich in organic carbon as sole carbon source. On defined media, only the monokaryon showed growth promotion by addition of slate. At the same time, metals were released from the slate and, after reaching a threshold concentration, inhibited further growth of the fungus. The proteome during decomposition of the black slate showed induction of proteins potentially involved in rock degradation and stress resistance, and the gene for laccase-like oxidase mco2 was up-regulated. Specifically in the dikaryon, the laccase gene lcc1 was induced, while lcc2 as well as mco1, mco3, and mco4 expression levels remained similar. Spectrophotometric analysis revealed that both life forms were able to degrade the rock and produce smaller particles.

Keywords: Schizophyllum commune; bioweathering; black slate; laccases; multicopper oxidases; proteome; rock.

FIGURE 1

Growth rate of Schizophyllum commune strains 4–39 and 12–43 × 4–39 in presence of black slate normalized to the corresponding control without black slate supplement. Positive values indicate a black slate induced burst of growth and negative values reveal a black slate induced inhibition of growth; dpi days after inoculation. Error bars represent standard deviation of three biological replicates.

FIGURE 2

S. commune growing in half diluted minimal medium without and with fractionized black slate (A), hyphal ball stained with Lactophenol Cotton Blue with inclusions of black slate (B), and hypha of monokaryon 4–39 with attached small black slate particles (C) 14 dpi.

FIGURE 3

Metal release from black slate into culture medium of black slate containing medium (BS) serving as control and black slate containing medium with fungal inoculum (BS + monokaryon); dpi days after inoculation. Missing data points are below the detection limit. Error bars represent standard deviation of three biological replicates.

FIGURE 4

Spectrophotometric analysis for measuring the degradation of black slate (BS) by S. commune; dpi days after inoculation. Error bars represent standard deviation of three biological replicates; ^∗p < 0.01, paired, two-tailed t-test.

FIGURE 5

FunCat annotated functions of proteins exclusively produced in presence (A) and absence (B) of black slate of S. commune strain 4–39.

FIGURE 6

FunCat annotated functions of proteins exclusively produced in presence (A) and absence (B) of black slate of S. commune strain 12–43 × 4–39.

FIGURE 7

Extracellular laccase activity in S. commune 12–43 × 4–39 growing without and with black slate (BS). Error bars represent standard deviation of three biological replicates; ^∗p < 0.05, paired, two-tailed t-test.

FIGURE 8

Relative expression of multicopper oxidases in S. commune 4–39 and 12–43 × 4–39 during black slate (BS) degradation, normalized by expression for treatments without black slate. Error bars represent standard deviation of three biological replicates.