Liu Gongwei, Zhang Ke, Gong Hanxuan, Yang Kaiyao, Wang Xiaoyu, Zhou Guangchen, Cui Wenyuan, Chen Yulin, Yang Yuxin
College of Animal Science and Technology, Northwest A&F University, Yangling, 712100, Shaanxi, China.
Qinling Giant Panda Breeding Research Center, Shaanxi Academy of Forestry Sciences, Zhouzhi, 710402, Shaanxi, China.
Biotechnol Biofuels Bioprod. 2023 Aug 19;16(1):130. doi: 10.1186/s13068-023-02375-3.
Lignocellulosic biomass is the most abundant and renewable terrestrial raw material for conversion into bioproducts and biofuels. However, the low utilization efficiency of lignocellulose causes environmental pollution and resource waste, which limits the large-scale application of bioconversion. The degradation of lignocellulose by microorganisms is an efficient and cost-effective way to overcome the challenge of utilizing plant biomass resources. This work aimed to screen valuable cellulolytic bacteria, explore its molecular mechanism from genomic insights, and investigate the ability of the strain to biodegrade wheat straw.
Bacillus subtilis (B. subtilis) RLI2019 was isolated from the intestine of Reticulitermes labralis. The strain showed comprehensive enzyme activities related to lignocellulose degradation, which were estimated as 4.06, 1.97, 4.12, 0.74, and 17.61 U/mL for endoglucanase, β-glucosidase, PASC enzyme, filter paper enzyme, and xylanase, respectively. Whole genome sequencing was performed to better understand the genetic mechanism of cellulose degradation. The genome size of B. subtilis RLI2019 was 4,195,306 bp with an average GC content of 43.54%, and the sequence characteristics illustrated an extremely high probability (99.41%) as a probiotic. The genome contained 4,381 protein coding genes with an average GC content of 44.20%, of which 145 genes were classified into six carbohydrate-active enzyme (CAZyme) families and 57 subfamilies. Eight cellulose metabolism enzyme-related genes and nine hemicellulose metabolism enzyme-related genes were annotated by the CAZyme database. The starch and sucrose metabolic pathway (ko00500) was the most enriched with 46 genes in carbohydrate metabolism. B. subtilis RLI2019 was co-cultured with wheat straw for 7 days of fermentation, the contents of neutral detergent fiber, acid detergent fiber, hemicellulose, and lignin were significantly reduced by 5.8%, 10.3%, 1.0%, and 4.7%, respectively. Moreover, the wheat straw substrate exhibited 664.9 μg/mL of reducing sugars, 1.22 U/mL and 6.68 U/mL of endoglucanase and xylanase activities, respectively. Furthermore, the fiber structures were effectively disrupted, and the cellulose crystallinity was significantly reduced from 40.2% to 36.9%.
The complex diversity of CAZyme composition mainly contributed to the strong cellulolytic attribute of B. subtilis RLI2019. These findings suggest that B. subtilis RLI2019 has favorable potential for biodegradation applications, thus it can be regarded as a promising candidate bacterium for lignocellulosic biomass degradation.
木质纤维素生物质是转化为生物产品和生物燃料最丰富且可再生的陆地原料。然而，木质纤维素的低利用效率导致环境污染和资源浪费，限制了生物转化的大规模应用。微生物降解木质纤维素是克服植物生物质资源利用挑战的一种高效且经济有效的方法。本研究旨在筛选有价值的纤维素分解菌，从基因组层面探索其分子机制，并研究该菌株对小麦秸秆的生物降解能力。
从黄胸散白蚁肠道中分离出枯草芽孢杆菌（B. subtilis）RLI2019。该菌株表现出与木质纤维素降解相关的综合酶活性，内切葡聚糖酶、β-葡萄糖苷酶、对硝基苯-β-D-纤维二糖酶、滤纸酶和木聚糖酶的活性分别估计为4.06、1.97、4.12、0.74和17.61 U/mL。进行全基因组测序以更好地理解纤维素降解的遗传机制。枯草芽孢杆菌RLI2019的基因组大小为4,195,306 bp，平均GC含量为43.54%，序列特征表明其作为益生菌的概率极高（99.41%）。该基因组包含4,381个蛋白质编码基因，平均GC含量为44.20%，其中145个基因被归类到六个碳水化合物活性酶（CAZyme）家族和57个亚家族中。CAZyme数据库注释了八个与纤维素代谢酶相关的基因和九个与半纤维素代谢酶相关的基因。淀粉和蔗糖代谢途径（ko00500）在碳水化合物代谢中富集程度最高，有46个基因。枯草芽孢杆菌RLI2019与小麦秸秆共培养7天进行发酵，中性洗涤纤维、酸性洗涤纤维、半纤维素和木质素的含量分别显著降低了5.8%、10.3%、1.0%和4.7%。此外，小麦秸秆底物表现出664.9 μg/mL的还原糖，内切葡聚糖酶和木聚糖酶活性分别为1.22 U/mL和6.68 U/mL。此外，纤维结构被有效破坏，纤维素结晶度从40.2%显著降低至36.9%。
CAZyme组成的复杂多样性主要促成了枯草芽孢杆菌RLI2019强大的纤维素分解特性。这些发现表明枯草芽孢杆菌RLI2019在生物降解应用方面具有良好潜力，因此可被视为木质纤维素生物质降解的有前景候选菌株。
