稻草微贮早期真菌群落演变及其木质纤维素降解酶的预测

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

摘要:

【背景】 木质纤维素的难降解性是导致稻草资源产量丰富却难以广泛用于牲畜饲料的根本原因。【目的】 研究稻草微贮早期发酵过程中真菌群落演变过程及真菌对木质纤维素的降解作用。【方法】 以1.2×10⁶ CFU/g-DM的地衣芽孢杆菌复合5×10⁶ CFU/g-DM的植物乳杆菌添加进行稻草微贮。于不同时间节点(1、3、7和15 d)进行internal transcribed spacer (ITS)真菌群落分析。【结果】 稻草微贮的第7天真菌群落多样性最高。发酵过程中的优势菌门依次为子囊菌门(Ascomycetes) (64.2%)和担子菌门(Basidiomycota) (30.2%)。与第1天相比，子囊菌门相对丰度分别在第7天和第15天均极显著升高(P<0.001)；担子菌门相对丰度在第7天和第15天均极显著降低(P<0.001)。优势菌属依次为汉纳菌属(Hannaella) (11.6%)、伊萨菌属(Issatchenkia) (8.1%)、哈萨克斯坦菌属(Kazachstania) (6.3%)、酿酒酵母属(Saccharomyces) (6.2%)、线黑粉酵母菌属(Filobasidium) (5.1%)。枝顶孢属(Acremonium) (2.4%)和曲霉属(Aspergillus) (2.2%)是发酵过程中的次优菌属。与第1天相比，汉纳菌属相对丰度在第15天极显著降低(P<0.001)；枝顶孢属和曲霉属相对丰度均在第7天极显著升高(P<0.001)。PICRUSt预测结果表明：β-葡萄糖苷酶、漆酶、α-半乳糖苷酶和β-甘露糖苷酶是丰度最高的木质纤维素降解酶。Spearman相关性分析结果表明，担子菌门与β-甘露糖苷酶有显著正相关关系(P<0.05)。汉纳菌属与β-葡萄糖苷酶和β-甘露糖苷酶有显著正相关关系(P<0.05)。枝顶孢属和曲霉属均与β-葡萄糖苷酶、β-甘露糖苷酶、漆酶和α-半乳糖苷酶有极显著正相关关系(P<0.001)。【结论】 在稻草微贮过程中，真菌对木质纤维素有降解作用。本文为真菌在微贮过程中的有效利用以及木质纤维素的生物降解提供了理论依据。

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.