Stewart Natalee, Feng Jingyang, Liu Xiaoping, Chaudhuri Devyani, Foster John W, Drolet Marc, Tse-Dinh Yuk-Ching
Department of Biochemistry and Molecular Biology, New York Medical College, Valhalla, NY 10595, USA.
Department of Microbiology and Immunology, University of South Alabama College of Medicine, Mobile, AL 36688, USA.
Microbiology (Reading). 2005 Aug;151(Pt 8):2783-2791. doi: 10.1099/mic.0.28022-0.
Acid resistance (AR) in Escherichia coli is important for its survival in the human gastrointestinal tract and involves three systems. The first AR system is dependent on the sigma factor RpoS. The second system (the GAD system) requires the glutamate decarboxylase isoforms encoded by the gadA and gadB genes. The third system (the ARG system) requires the arginine decarboxylase encoded by adiA. Loss of topoisomerase I function from topA deletion or Tn10 insertion mutations lowered the resistance to killing by pH 2 or 2.5 treatment by 10-fold to >100-fold. The RpoS and GAD systems were both affected by the topA mutation, but the ARG system of AR was not affected. Northern blot analysis showed that induction of gadA and gadB transcription in stationary phase and at pH 5.5 was decreased in the topA mutant. Western blot analysis showed that the topA mutation did not affect accumulation of RpoS, GadX or GadW proteins. Topoisomerase I might have a direct influence on the transcription of AR genes. This influence does not involve R-loop formation as the overexpression of RNase H did not alleviate the decrease of AR caused by the topA mutation. The effect of the topA mutation could be suppressed by an hns mutation, so topoisomerase I might be required to counteract the effect of H-NS protein on gene expression, in addition to its influence on RpoS-dependent transcription.
大肠杆菌中的耐酸性（AR）对其在人体胃肠道中的存活至关重要，且涉及三个系统。第一个AR系统依赖于σ因子RpoS。第二个系统（GAD系统）需要由gadA和gadB基因编码的谷氨酸脱羧酶同工型。第三个系统（ARG系统）需要由adiA编码的精氨酸脱羧酶。因topA缺失或Tn10插入突变导致拓扑异构酶I功能丧失，使对pH 2或2.5处理的杀伤抗性降低了10倍至>100倍。RpoS和GAD系统均受topA突变影响，但AR的ARG系统不受影响。Northern印迹分析表明，在topA突变体中，稳定期和pH 5.5时gadA和gadB转录的诱导减少。Western印迹分析表明，topA突变不影响RpoS、GadX或GadW蛋白的积累。拓扑异构酶I可能对AR基因的转录有直接影响。这种影响不涉及R环形成，因为RNase H的过表达并未减轻topA突变引起的AR降低。topA突变的影响可被hns突变抑制，因此拓扑异构酶I除了影响RpoS依赖性转录外，可能还需要抵消H-NS蛋白对基因表达的影响。
