FlhA influences Bacillus thuringiensis PlcR-regulated gene transcription, protein production, and virulence
FlhA influences Bacillus thuringiensis PlcR-regulated gene transcription, protein production, and virulence
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DOI：
10.1128/aem.71.12.8903-8910.2005
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发表时间：
2005-12-01
影响因子：
4.4
通讯作者：
Nielsen-LeRoux, C
中科院分区：
文献类型：
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作者：
Bouillaut, L;Ramarao, N;Nielsen-LeRoux, C
苏云金芽孢杆菌和蜡状芽孢杆菌关系密切。B。苏云金杆菌因其昆虫病原特性而众所周知，这主要是由于质粒编码的晶体毒素的合成。B。蜡样芽胞杆菌似乎是一种新兴的机会性人类病原体。B。苏云金杆菌和B.蜡状芽孢杆菌产生许多推定的毒力因子，这些毒力因子受多效性转录调节因子PlcR的正调控。plcR的失活降低但不消除毒力，表明其他因素如鞭毛可能有助于致病性。因此，我们进一步分析了突变体（B.苏云金杆菌407 Cry（-）Delta flhA）先前被描述为在鞭毛装配和运动性以及溶血素BL和磷脂酶的产生方面存在缺陷。通过二维电泳分析获得了分泌蛋白的大图片，其显示鞭毛蛋白不分泌，并且在flhA突变体中减少了几种毒力相关因子的产生。此外，我们定量了FlhA对plcA和hblC基因转录的影响。结果显示flhA突变导致plcA和hblC转录的显著降低。这些结果表明，几个PlcR调控的毒力因子的转录与鞭毛器协调。一致地，flhA突变体也显示出对HeLa细胞的细胞毒性和对大蜡螟幼虫经口和血腔内接种后的毒力的强烈降低。毒力的降低可能是由于缺乏鞭毛和分泌因子的产量降低。因此，FlhA似乎是具有多效性作用的重要毒力因子。
Bacillus thuringiensis and Bacillus cereus are closely related. B. thuringiensis is well known for its entomopathogenic properties, principally due to the synthesis of plasmid-encoded crystal toxins. B. cereus appears to be an emerging opportunistic human pathogen. B. thuringiensis and B. cereus produce many putative virulence factors which are positively controlled by the pleiotropic transcriptional regulator PlcR. The inactivation of plcR decreases but does not abolish virulence, indicating that additional factors like flagella may contribute to pathogenicity. Therefore, we further analyzed a mutant (B. thuringiensis 407 Cry(-) Delta flhA) previously described as being defective in flagellar apparatus assembly and in motility as well as in the production of hemolysin BL and phospholipases. A large picture of secreted proteins was obtained by two-dimensional electrophoresis analysis, which revealed that flagellar proteins are not secreted and that production of several virulence-associated factors is reduced in the flhA mutant. Moreover, we quantified the effect of FlhA on plcA and hblC gene transcription. The results show that the flhA mutation results in a significant reduction of plcA and hblC transcription. These results indicate that the transcription of several PlcR-regulated virulence factors is coordinated with the flagellar apparatus. Consistently, the flhA mutant also shows a strong decrease in cytotoxicity towards HeLa cells and in virulence against Galleria mellonella larvae following oral and intrahemocoelic inoculation. The decrease in virulence may be due to both a lack of flagella and a lower production of secreted factors. Hence, FlhA appears to be an essential virulence factor with a pleiotropic role.