Sweet sorghum is a promising crop for a warming, drying African climate, and basic information is lacking on conversion pathways for its lignocellulosic residues (bagasse). Brown rot wood-decomposer fungi use carbohydrate-selective pathways that, when assessed on sorghum, a grass substrate, can yield information relevant to both plant biomass conversion and fungal biology. In testing sorghum decomposition by brown rot fungi (Gloeophyllum trabeum, Serpula lacrymans), we found that G. trabeum readily degraded sorghum, removing xylan prior to removing glucan. Serpula lacrymans, conversely, caused little decomposition. Ergosterol (fungal biomarker) and protein levels were similar for both fungi, but S. lacrymans produced nearly 4x lower polysaccharide-degrading enzyme specific activity on sorghum than G. trabeum, perhaps a symptom of starvation. Linking this information to genome comparisons including other brown rot fungi known to have a similar issue regarding decomposing grasses (Postia placenta, Fomitopsis pinicola) suggested that a lack of CE 1 feruloyl esterases as well as low xylanase activity in S. lacrymans (3x lower than in G. trabeum) may hinder S. lacrymans, P. placenta, and F. pinicola when degrading grass substrates. These results indicate variability in brown rot mechanisms, which may stem from a differing ability to degrade certain lignin-carbohydrate complexes.
Bibliographical noteFunding Information:
This work was funded in part by the US Department of Energy (DOE) Office of Science (Early Career Grant DESC0004012 to Jonathan S. Schilling, from the Office of Biological and Ecological Research (BER), and BER Grant DE-SC0012742 to Jonathan S. Schilling). This work was also funded by the National Science Foundation Graduate Research Fellowship Programs under Grant no. 00039202 to Gerald N. Presley, an international travel allowance through the Graduate Research Opportunities Worldwide (GROW), and a United States Agency for International Development Research and Innovations Fellowship through the US Global Development Lab (Grant no. AID-LAB-T-15-00002) to Gerald N. Presley.