State Key Laboratory of Microbial Technology, Shandong University, Qingdao, 266237, PR China.
State Key Laboratory of Biobased Material and Green Papermaking, Qilu University of Technology, Shandong Academy of Science, Jinan, 250353, PR China.
J Biotechnol. 2019 Apr 10;295:55-62. doi: 10.1016/j.jbiotec.2019.02.010. Epub 2019 Mar 7.
Endoglucanase, an important component of cellulases, is used as additives in ensiling of forage crops. However, its detailed role is unclear in ensilages. In the present study, two endoglucanases Cel5 and Cel9 produced by strain Paenibacillus panacisoli SDMCC050309, previously isolated from ensiled corn stover, were identified in the cultures by microcrystalline cellulose absorption coupled with zymogram analysis. After heterologously expressed in Escherichia coli DE3 and purified, these two proteins were biochemically characterized. Cel5 was 61 kDa and showed maximal activity at pH 7.0 and 45 °C, while the maximum activity was at pH 8.0 and 65 °C for Cel9 with 97 kDa in size. Both of them could degrade carboxymethyl cellulose into cellooligosaccharides, in which cellobiose and cellotriose could be used as substrates for the growth of homofermentative strains Lactobacillus plantarum CGMCC6888 and L. farciminis CCTCC AB2016237, but not for the heterofermentative strains L. brevis SDMCC050297 and L. parafarraginis SDMCC050300. Therefore, we concluded that the added endoglucanase contributed to enhance the growth of homofermentative lactic acid bacteria for high level of lactic acid production in ensilages.
内切葡聚糖酶是纤维素酶的重要组成部分，作为添加剂被用于青贮饲料作物的青贮过程中。然而，其在青贮中的详细作用尚不清楚。在本研究中，先前从青贮玉米秸秆中分离到的解淀粉芽孢杆菌 SDMCC050309 产生的两种内切葡聚糖酶 Cel5 和 Cel9 通过微晶纤维素吸收与同工酶分析相结合在培养物中被鉴定出来。在大肠杆菌 DE3 中异源表达并纯化后，对这两种蛋白质进行了生化特性分析。Cel5 分子量为 61kDa，在 pH7.0 和 45°C 时具有最大活性，而 Cel9 的最大活性在 pH8.0 和 65°C，分子量为 97kDa。这两种酶都可以将羧甲基纤维素降解为纤维寡糖，其中纤维二糖和纤维三糖可以作为同型发酵菌株植物乳杆菌 CGMCC6888 和 L. farciminis CCTCC AB2016237 的生长底物，但不能作为异型发酵菌株 L. brevis SDMCC050297 和 L. parafarraginis SDMCC050300 的生长底物。因此，我们得出结论，添加的内切葡聚糖酶有助于增强同型发酵乳杆菌的生长，从而在青贮过程中产生高水平的乳酸。
