嗜热链球菌谷氨酸脱羧酶基因及其侧翼区序列分析

Sequence Analysis of Glutamate Gecarboxylase Gene and Flanking Regions from Streptococcus thermophilus Y-2

从嗜热链球菌Streptococcus thermophilus Y-2的谷氨酸脱羧酶基因(gadB)及其两侧旁邻序列出发,在GenBank中分别用Blastn、Blastx搜索同源序列。gadB在核酸水平上无法找到同源序列,在蛋白质水平上与多种细菌的谷氨酸脱羧酶同源。根据谷氨酸脱羧酶的氨基酸序列构建系统发育树,菌株Y-2与具核梭杆菌Fusobacterium nucleatumsubsp.polymorphum ATCC10953的亲缘关系最近。gadB的上游侧翼区与嗜热链球菌LMG18311的插入序列IS1216转座酶基因具有很高的相似性。gadB的下游侧翼区在核酸水平上未找到同源序列,在蛋白质水平上与谷氨酸/γ-氨基丁酸转运蛋白有很高的相似性。菌株Y-2的gadB、gadC排列方式与大肠杆菌、弗氏志贺菌的相同,而与乳酸乳球菌、短小乳杆菌的相反。在已完成全基因组测序的3个模式株Streptococcus thermophilus LMG18311、CNRZ1066、LMD-9中均含有插入序列IS1216,但未发现谷氨酸脱羧酶基因gadB、谷氨酸/γ-氨基丁酸转运蛋白基因gadC。

The glutamate decarboxylase gene （gadB） and its flanking regions from Streptococcus thermophilus Y-2 were investigated by homologous search in GenBank with Blastn and Blastx. There was no any other gene showing significant similarity with gadB, while the protein product of gadB had high similarity with several bacterial glutamate decarboxylases. Phylogenetic tree based on glutmamte decarboxylase sequences indicated that Fusobacterium nucleatum subsp, polymorphum ATCC 10593 showed the closest relationship with S. thermophilus Y-2. The upstream flanking region ofgadB was homologous to bacterial transposases, while the downstream flanking region of gadB encoding a putative protein was similar to bacterial glutamate/y-aminobutyric acid antiporters （GadC）. The order of gadB and gadC in S. thermophilus Y-2 genome was similar to that of E. coli and Shigellaflexneri, but different from that of Lactococcus lactis and Lactobacillus brevis. Insertion sequence IS 1216 was present in genomes of S. thermophilus LMG 18311, CNRZ1066, and LMD-9, but not gadB or gadC.