大肠杆菌O141 O-抗原基因簇的破译及进化分析

对大肠杆菌O141 O-抗原基因簇进行测序，序列全长15601bp，用生物信息学的方法进行序列分析，共发现12个基因：鼠李糖合成酶基因(rmlB，rmlD，rmlA，rmlC)、甘露糖合成酶基因(manB，manC)，糖基转移酶基因(orf6，orf7，orf9，orf10)、O-抗原转运酶基因(wzx)和O-抗原聚合酶基因(wzy)。用PCR的方法筛选出了针对大肠杆菌O141的特异基因，可以用于基因芯片或PCR方法对大肠杆菌O141的快速检测。通过对大肠杆菌O141的O-抗原基因簇及甘露糖和鼠李糖合成酶基因的进化分析发现：大肠杆菌O141 O-抗原基因簇是低GC含量的片段，仅O-抗原特异的基因才出现在O-抗原基因簇；并且这些基因可能介导了O-抗原基因簇间的重组及以O141 O-抗原基因簇的形成。

Sequence of Escherichia coli O141 O-antigen Gene Cluster and Analyses of Its Evolutionary History

Lipopolysaccharide(LPS) is one of the major components of the outer membrane of gram-negative bacteria .It is an amphipathic molecule compose of lipid A ,a core oligosaccharide and an O-specific antigen.O-antigen,which is a repeat-unit polysaccharide,is a major contribution to the antigenic variability of the bacterial cell surface.The genes of O-antigen gene cluster are responsible for the synthesis of the O-antigen.The O-antigen gene cluster of E.coli O141 was sequenced and found to contain the genes rmlBDAC and manBC for the biosynthesis of nucleotide sugars dTDP-rhamnose and GDP-mannose,respectively,encoding genes for Ounit flippase(wzx),O-antigen polymerase(wzy) and potential transferase genes.The possible biosynthesis pathway for O-antigen of E.coli O141 was proposed.Two genes specific to E.coli O141 were identified.This work provides the basis for a sensitive test by PCR for the rapid detection of E.coli O141.Phylogenetic trees for the rmlB,rmlD,rmlA,and rmlC genes and manB,manC genes were generated and the comparisons were made among different strains.We find that these genes are typical E.coli genes and might have been involved in recombination events between O-antigen gene clusters.