Synergy between pretreatment lignocellulose modifications and saccharification efficiency in two brown rot fungal systems

Brown rot wood-degrading fungi distinctly modify lignocellulose and completely hydrolyze polysaccharides (saccharification), typically without secreting an exo-acting glucanase and without removing lignin. Although each step of this two-step approach evolved within the same organism, it is unknown if the early lignocellulose modifications are made to specifically facilitate their own abbreviated enzyme system or if enhancements are more general. Because commercial pretreatments are typically approached as an isolated step, answering this question has immense implication on bioprocessing. We pretreated spruce and pine blocks with one of two brown rot fungi, Gloeophyllum trabeum or Fomitopsis pinicola. Wood harvested at weeks 1, 2, 4, and 8 showed a progression of weight loss from time zero due to selective carbohydrate removal. Hemicellulose losses progressed faster than cellulose loss. This “pretreated” material was then saccharified with commercially relevant Trichoderma reesei cellulases or with cellulases from the brown rot fungi responsible for degrading the wood to test for synergy. With increased decay, a significant increase in saccharification efficiency was apparent but not limited to same-species enzyme sources. We also calculated total sugar yields, and calculations that compensate for sugars consumed by fungi suggest a shorter residence time for fungal colonization than calculations based solely on saccharification yields.