中文摘要：

为了了解次黄嘌呤核苷酸脱氢酶（IMPDH）对猪链球菌2型GN061215致病力的影响机制，利用同源重组技术，敲除猪链球菌2型GN061215的impdh基因，重组后的GN061215命名为GN061215（△IMPDH），比较GN061215与GN061215（△IMPDH）培养特性、生化特性、致病力以及基因转录水平差异。结果显示impdh基因敲除后，引起GN061215生长曲线迟缓期延长，降低了GN061215生长曲线平台期OD600峰值，同时截短了GN061215菌株成链长度；GN061215、GN061215（△IMPDH）对46种代谢底物利用能力一致，对2种代谢底物利用存在差异；GN061215（△IMPDH）对Balb／c小鼠的致病力较GN061215菌株有一定程度的下降。SDS-PAGE显示GN061215（△IMPDH）菌体的粗提蛋白质条带较GN061215有显著减少；基因芯片比较GN061215、GN061215（△IMPDH）基因转录差异发现，下调基因中存在36个关联核糖体大、小亚基合成的基因，而在上调基因中不存在该类基因，表明impdh基因的丢失影响了GN061215菌株核糖体大、小亚基的合成，进而显著减少了GN061215菌株菌体蛋白质的表达，这可能与GN061215菌株毒力的下降有关。

英文摘要：

To study the mechanism of inosine monophosphate dehydrogenase （IMPDH） on the pathogenicity of Streptococcus suis serotype 2 （SS2）, impdh gene in SS2 strain GN061215 was replaced with cat gene via homologous recombination, and the recombinant SS2 was named GN06t215 （△IMPDH）. To assess the effects of the impdh gene in GN061215, the growth features, biochemical characteristics, virulence in Balb/c mice and differences in the level of gene transcription were compared between the GN061215 （△IMPDH） and GN061215. The results showed that impdh knockout prolonged the lag phase in the growth curve of GN061215, lowered peak of OD6oo in stationary phase, and truncated the chain length of GN061215. Except for two other substrates, the utilization of 46 substrates by GN061215 （ △IMPDH）and GN061215 was identical. SDS- PAGE demonstrated GN061215 （△IMPDH） expressed significantly less cell protein compared with GN061215. Results of microarray revealed 487 genes were down-regulated in GN061215 （ △ IMPDH）, and among which 36 genes were associated with ribosomal large and small units. However, there was no up-regulated gene associated with ribosomal large and small u- nits in GN061215 （ △IMPDH）. These phenomena gave a hypothesis knocking out impdh gene inhibited expression of ribosomal large and small units in GN061215, and consequently reduced the expression of cell protein in GN061215, leading to the decline of the virulence of GN061215.