Pre-pasteurization enhances the fermentation of wheat straw by Irpex lacteus: Chemical composition, enzymatic hydrolysis, and microbial community

Abstract

Pasteurization is an economical and convenient method to eliminate harmful microorganisms in raw materials for fermentation. However, the surviving species in pasteurized wheat straw and their potential effects on white rot fungi fermentation remain unclear. In this study, wheat straw was pasteurized at different temperatures (60–85 ℃) and fermented with Irpex lacteus for 28 days. At the end of fermentation, the acid-insoluble lignin (ADL) content decreased significantly in all pasteurized samples (P < 0.05). We found a negative correlation between ADL content and pasteurization temperature (R =0.992, P < 0.001). In enzymatic hydrolysis, the sugar yield of samples pasteurized at 80 ℃ (T80) was higher 39.9% than that at 60 ℃. Regarding microbial community, I. lacteus was the dominant fungus in T80 at an abundance of 93.4%, whereas the abundance of other fungi, such as Chaetomium and Aspergillus, was below 1.60%. Three bacteria, including Bacillus, Lysinibacillus, and Paenibacillus, had a combined abundance of 80.5% in T80, which could be attributed to their high-temperature tolerance and symbiosis with I. lacteus. Bacterial functions, such as nitrogen cycling, cellulolysis, chitinolysis, and methylotrophy, were enriched in T60 samples, but the functions and those related to human and animal pathogen reduced in T80 samples, which promoted the growth and degradation of I. lacteus. Overall, thermotolerant fungi and spore-forming bacterial species are the dominant microorganisms in wheat straw pasteurized above 80 ℃, which promotes the colonization and degradation of I. lacteus and improves the biosafety of treated wheat straw.