大肠埃希菌Ⅰ型菌毛fimA基因的克隆和序列比较分析

Cloning,sequencing and comparision analysis of Escherichia coli type Ⅰ fimbriae fimA gene

通过设计1对fimA全基因通用引物,对已知不同人、动物源的17株大肠埃希菌菌株的Ⅰ型菌毛fimA基因进行PCR扩增、克隆和测序,并与GenBank中9株菌株序列进行同源性比较分析,探讨I型菌毛宿主嗜性。结果表明：17株菌株均能扩增出约549bp的预期大小目的片段。克隆和序列分析显示,26株不同来源的大肠埃希菌fimA基因的核苷酸同源性为88.7%-100%,推导氨基酸同源性为88%-100%,其中出现差异的31个易发生突变的位点多为中性氨基酸,其中10株菌的fimA序列于第26个氨基酸位置连续插入了脯氨酸和苏氨酸,且80%为猪源大肠埃希菌,因此提示I型菌毛在大肠埃希菌的进化过程中可能具备一定的宿主嗜性。

In this study,apair of primers was designed for PCR-amplification of fimAgene,sequentially PCR products from nine different E.coli strains were cloned and sequenced.Sequenced data was aligned and analyzed with eight other sequences of different strains from GenBank data.The results showed that a 549 bp positive PCR product could be amplified and confirmed from all nine strains.Further analysis showed that the nucleotide homology of fimA gene in26 different E.coli strains from various origins were between 88.7%-100%,and the homology of amino acid encoded by fimAof various strains were between 88.0%-100%.Among these,31 easily mutated loci were mostly neutral amino acids.Interestingly,we found that the 10 strains of the genes fimAsequences had two amino acids,proline and threonine,inserted at the 26 th AA position.80% of the E.coli strains was from porcine origin,implying that the type I fimbriae in the course of the evolution of E.coli may be related to host tropism,but its specific mechanism of action remains to be further studied.