Loss of genes involved in lignin degradation: an energetic advantage for brown rot fungi responsible for the persistence of lignin in forest soil?

Dr Nicolas Valette1,2, Pr Eric Gelhaye2, Dr Gry Alfredsen3, Pr Barry Goodell4, Dr Delphine Derrien1

1INRA, Biogeochemistry of Forest Ecosystems, Nancy, France, 2INRA-Lorraine University, Interactions Arbres Micro-organismes, Nancy, France, 3Norwegian institute of bioeconomy reseach, As, Norway, 4University of Massachusetts, Departement of microbiology, Amherst, USA

Forest soils represent a third of the terrestrial area and have a key role in carbon cycle and climate mitigation, as they store between 50 and 80% of the global stock of soil organic carbon (SOC). The major precursor of forest SOC is the dead wood. It is mainly composed by three polymers (cellulose, hemicellulose and lignin), which are attacked by saprophytic fungi represented by two main groups: brown rot fungi and white rot fungi. Both of them mineralize the wood polysaccharides into CO2. However, only white rot fungi are able to mineralize lignin thanks to their specific enzymatic systems. Brown rot simply modify the lignin chemically using hydroxy radicals in a mediated-Fenton reaction. The brown rot fungi have evolved from ancestral white rot fungi in processes accompanied by a loss of the genes coding for enzymes involved in lignin degradation. Despite this event being a relatively recent event, brown rot fungi dominate coniferous forest ecosystems. We hypothesize that the imbalance between the energy gained from organic substrate degradation and the energy expended to produce degradation agents provides an advantage to brown rot fungi compared to white rot fungi. To test this hypothesis, we inoculated wood sawdust either with Gloeophyllum trabeum a brown rot fungus or Trametes versicolor a white rot fungus. CO2 production, microbial biomass, change in substrate chemistry and enzyme production were monitored over time to compare the energy costs and gains associated with the wood sawdust biodegradation. The data generated were fitted in a mathematical model, which computed the energy budget for the two root degradative pathways to provide new insights on the persistence of lignin in soil.

Biography: To be confirmed.

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