Rice straw in early stage of microbial fermentation: fungal community dynamics and lignocellulose-degrading enzymes

Abstract:

[Background] Despite the abundant production, rice straw is rarely used as animal feed because of the difficulty in degrading lignocellulose. [Objective] To investigate the fungal community dynamics in rice straw over time and the degradation of lignocellulose by fungi in the early stage of microbial fermentation.[Methods] Rice straw was inoculated with 1.2×10⁶ CFU/g-DM of Bacillus licheniformis and 5×10⁶ CFU/g-DM of Lactobacillus plantarum for microbial fermentation. The ITS sequencing was performed to analyze the fungal community on days 1, 3, 7, and 15. [Results] The highest fungal diversity was observed on day 7. The dominant phyla during fermentation were Ascomycetes (64.2%) and Basidiomycota (30.2%). Compared with that on day 1, the relative abundance of Ascomycota increased on day 7and day 15 (P<0.001), and that of Basidiomycota decreased on day 7 and day 15 (P<0.001). The dominant genera included Hannaella (11.6%), Issatchenkia (8.1%), Kazachstania (6.3%), Saccharomyces (6.2%), Filobasidium (5.1%), Acremonium (2.4%), and Aspergillus (2.2%). Compared with that on day 1, the relative abundance of Hannaella decreased on day 15 (P<0.001) and that of Acremonium and Aspergillus increased on day 7 (P<0.001). PICRUSt predictions indicated that β-glucosidase, laccase, α-galactosidase, and β-mannosidase were the most abundant lignocellulose-degrading enzymes. The results of Spearman correlation analysis showed that Ascomycota had a positive correlation with β-mannosidase (P<0.05). Hannaella was positively correlated with β-glucosidase and β-mannosidase (P<0.05). In addition, both Acremonium and Aspergillus showed strong positive correlations with β-glucosidase, β-mannosidase, laccase, and α-galactosidase (P<0.001). [Conclusion] During the microbial fermentation of rice straw, fungi degrade the lignocellulose. This paper presents theoretical underpinnings for the efficient use of fungi in the microbial fermentation and the biodegradation of lignocellulose.