Fiber Digestion by Rumen Ciliate Protozoa
Fiber Digestion by Rumen Ciliate Protozoa
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DOI：
10.1264/jsme2.19.203
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发表时间：
2004-09
影响因子：
2.2
通讯作者：
A. Takenaka;K. Tajima;M. Mitsumori;H. Kajikawa
中科院分区：
文献类型：
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作者：
A. Takenaka;K. Tajima;M. Mitsumori;H. Kajikawa
对瘤胃纤毛虫纤维分解酶的研究相对滞后于瘤胃细菌和真菌。近年来，分子生物学的发展加强了对瘤胃原虫的研究，积累了大量的信息。本文综述了各种瘤胃纤毛虫无细胞提取物的纤维素分解活性。大的Ophyroxecidae，如Epidinium，Polyplastron和Eudiplodinium具有较高水平的内切葡聚糖酶和木聚糖酶活性。另一方面，内甲藻属（Entodinium spp.）只有微弱的活性来降解植物纤维。主要内切葡聚糖酶的分子量似乎小于40 k道尔顿，并且内切葡聚糖酶具有结合纤维素的能力。从尾甲藻（Epidiniumcaudatum）和多囊多膜藻（Polyplastronmultivesuculatum）的cDNA文库中克隆了8个纤溶酶基因，并在GenBank中注册。这8个克隆中有4个与糖苷水解酶家族5内切葡聚糖酶（GHF 5）基因具有高度同源性。其余4个与木聚糖酶基因（GHF 10和GHF 11）具有同源性。原生动物基因的鸟嘌呤（G）+胞嘧啶（C）含量（mol%）约为30%，密码子使用具有特异性，与其他微生物的内切葡聚糖酶或木聚糖酶基因不同。与瘤胃细菌（25%）和真菌基因（27%）中的赖氨酸密码子不同，原虫ORF中的赖氨酸密码子主要（约90%）为AAA。第5家族内切葡聚糖酶的系统发育树显示，4种纤毛虫的内切葡聚糖酶亲缘关系较近，形成一个簇。另一方面，这些纤毛虫的木聚糖酶似乎更密切相关的木聚糖酶从革兰氏阳性细菌，如瘤胃球菌和梭菌比其他木聚糖酶的真核生物来源。
The study of fibrolytic enzymes of rumen ciliate protozoa has lagged behind that of rumen bacteria and fungi. However, molecular biology has enhanced the investigation of rumen protozoa, and significant information has been accumulated in the last decade. The cellulolytic activities of cell-free extracts from each species of rumen ciliate protozoa have been summarized. Large Ophyroscolecidae such as Epidinium, Polyplastron, and Eudiplodinium have higher levels of endoglucanase and xylanase activity. On the other hand, Entodinium spp. have only weak activity to degrade plant fibers. The molecular weight of the main endoglucanase appears to be less than 40k Daltons, and the endoglucanases have the ability to bind cellulose. A total of eight fibrolytic enzyme genes have been cloned from cDNA libraries of Epidinium caudatum and Polyplastron multivesuculatum, and have been registered in GenBank. Four of these 8 clones have high homology with glycoside hydrolase family 5 endoglucanase (GHF5) genes. The remaining four have homology with xylanase (GHF10 and GHF11) genes. The guanine (G)+cytocine (C) content (mol%) of protozoal genes is about 30% and the codon usage is specific and different from that of the endoglucanase or xylanase genes originating from other microorganisms. The codon for Lys in the protozoal ORF is mainly (about 90%) AAA, unlike the Lys codons in rumen bacteria (25%) and the fungal gene (27%). The phylogenetic tree for family 5 endoglucanases shows that the endoglucanases of four ciliates are closely related to each other and form a cluster. On the other hand, the xylanases of these ciliates appear more closely related to xylanases from gram-positive bacteria such as Ruminococcus and Clostridium than to other xylanases of eukaryotic origin.