鼠傷寒沙門氏菌FimZ 蛋白質可調控不同生理功能

Abstract

鼠傷寒沙門氏菌會產生第一型線毛，第一型線毛的產生對於鼠傷寒沙門氏菌在定殖上扮演重要的角色。在鼠傷寒沙門氏菌中第一型線毛的表現，主要是藉由fim 基因組內的 fimZ、 fimY、 stm0551、fimW和fimU作為調控因子。其中FimZ屬於two-component regulatory system的反應調控蛋白，能夠活化第一型線毛主要次單位fimA基因的表現。在細菌體內，這類的調控蛋白並不罕見，他們除了能夠影響同源基因外，也可能會調控其他基因的表現。因此在本研究中想探討鼠傷寒沙門氏菌的FimZ除了參與第一型線毛的調控之外，對於其他生理功能是否也有影響。過去實驗室已在S. Typhimurium LB5010與ATCC 14028菌株，利用同源基因交換方法建構出fimZ基因剔除突變株。而在轉錄基因體學的分析上得知，S. Typhimurium LB5010 fimZ的剔除，會造成氧化緊迫相關基因cpxP、soxS以及第一型線毛相關基因fimA-fimF與 fimW表現下降；卻使plasmid-encoded fimbriae、菌株的趨化性、鞭毛還有毒力相關基因virK表現上提升。利用紙錠擴散試驗的方法來進行氧化緊迫反應的分析，相較於parental strain，fimZ突變株對於 H2O2 及paraquat 更具敏感性。在互補試驗中，利用陰溝腸桿菌的fimZ基因片段，卻無法在fimZ突變株回復氧化緊迫反應和第一型線毛的表現。LB5010及ATCC 14028的fimZ突變株均顯示低於parental strains的生長能力。ATCC 14028的fimZ突變株接種在soft agar中展現較強的移動能力，而接種LB5010 fimZ突變株沒有觀察到移動增加的情形。利用Caco-2 細胞株進行黏附試驗評估，發現LB5010或ATCC14028個別菌株的parental strain吸附細胞的能力都比其fimZ突變株來得強。而在Caco-2細胞株入侵試驗結果顯示，fimZ基因的缺損與否並無法造成顯著性的影響。我們的研究顯示fimZ基因產物可能會調控第一型線毛的表現及其他的生理功能。fimZ與其他標的基因交互作用的機制值得更進一步探討。

Salmonella enterica serovar Typhimurium produces type 1 fimbriae and such appendages play a significant role in colonization for S. Typhimurium. Expression of type 1 fimbriae in S. Typhimurium is primarily mediated by fimZ, fimY, stm0551, fimW, and fimU within the fim gene cluster. FimZ belongs to the response regulator of the two-component regulatory system in bacteria and has been shown to activate the expression of the fimbrial major subunit gene fimA. It is not uncommon that those regulatory proteins in bacteria regulate other target genes besides their cognate ones. Therefore, this study would like to investigate if FimZ affects other physiological functions other than type 1 fimbrial regulation. A fimZ mutant in S. Typhimurium LB5010 and ATCC 14028 were constructed by allelic exchange previously and were subjected to transcriptomic analysis by microarray. Our results revealed that the stress response related gene cpxP, soxS and type 1 fimbriae related genes fimA-fimF, and fimW were down-regulated, whereas plasmid-encoded fimbriae, chemotaxis, flagella associated genes and virulence genes like virK were up-regulated in the fimZ mutant strain. Oxidative stress response assay was performed with disc diffusion method and indicated that the fimZ mutant was more sensitive to H2O2 and paraquat than its parental strain. However, a homologue of fimZ from Enterobacter cloacae could not complement the fimZ mutant in the oxidative stress response and type 1 fimbrial expression. Both fimZ mutants in LB5010 and ATCC14028 exhibited decreased growth rate than their parental strains. Elevated motility phenotype on the soft agar was observed in ATCC 14028 fimZ mutant, but not in LB5010 fimZ mutant. Adhesion assays was evaluated by infecting Caco-2 cells with bacteria. The LB5010 and ATCC 14028 exhibited better adherent ability than their respective fimZ mutant strains. However, the absence or presence of fimZ gene did not affect the invasion ability of those strains to Caco-2 cells. Our study may indicate that fimZ gene product of S. Typhimurium could regulate type 1 fimbrial expression and other physiological functions as well. The mechanisms pertinent to cross-talk between fimZ and other target genes warrant further study.