Young G M, Amid D, Miller V L
Department of Microbiology and Molecular Genetics, University of California, Los Angeles, 90095, USA.
J Bacteriol. 1996 Nov;178(22):6487-95. doi: 10.1128/jb.178.22.6487-6495.1996.
To infect a susceptible host, the gastrointestinal pathogen Yersinia enterocolitica must survive passage through the acid environment of the stomach. In this study, we showed that Y. enterocolitica serotype O8 survives buffered acidic conditions as low as pH 1.5 for long periods of time provided urea is available. Acid tolerance required an unusual cytoplasmically located urease that was activated 780-fold by low-pH conditions. Acid tolerance of Helicobacter species has also been attributed to urease activity, but in that case urease was not specifically activated by low-pH conditions. A ure mutant strain of Y. enterocolitica was constructed which was hypersensitive to acidic conditions when urea was available and, unlike the parental strain, was unable to grow when urea was the sole nitrogen source. Examination of other urease-producing gram-negative bacteria indicated that Morganella morganii survives in acidic conditions but Escherichia coli 1021, Klebsiella pneumoniae, Proteus mirabilis, Providencia stuartii, and Pseudomonas aeruginosa do not. Consistent with these results, biochemical evidence demonstrated that Y. enterocolitica and M. morganii ureases were activated in vitro by low pH with an unusually low activity optimum of pH 5.5. In whole cells activation occurred as medium values decreased below pH 3.0 for Y. enterocolitica and pH 5.5 for M. morganii, suggesting that in vivo activation occurs as a result of cytoplasmic acidification. DNA sequence analysis of portions of the M. morganii ure locus showed that the predicted primary structure of the enzyme structural subunits is most similar to those of Y. enterocolitica urease. One region of similarity between these two ureases located near the active site is distinct from most other ureases but is present in the urease of Lactobacillus fermentum. This region of similarity may be responsible for the unique properties of the Y. enterocolitica and M. morganii ureases since the L. fermentum urease also has been shown to have a low pH optimum for activity.
为了感染易感宿主，肠道病原体小肠结肠炎耶尔森氏菌必须在通过胃的酸性环境时存活下来。在本研究中，我们发现，只要有尿素，小肠结肠炎耶尔森氏菌O8血清型就能在低至pH 1.5的缓冲酸性条件下长时间存活。耐酸性需要一种特殊的位于细胞质中的脲酶，该脲酶在低pH条件下被激活780倍。幽门螺杆菌的耐酸性也归因于脲酶活性，但在那种情况下，脲酶不会被低pH条件特异性激活。构建了小肠结肠炎耶尔森氏菌的脲突变株，当有尿素时，该突变株对酸性条件高度敏感，并且与亲本菌株不同，当尿素是唯一氮源时无法生长。对其他产脲酶的革兰氏阴性菌的检测表明，摩根氏摩根菌能在酸性条件下存活，但大肠杆菌1021、肺炎克雷伯菌、奇异变形杆菌、斯氏普罗威登斯菌和铜绿假单胞菌则不能。与这些结果一致，生化证据表明，小肠结肠炎耶尔森氏菌和摩根氏摩根菌的脲酶在体外被低pH激活，其活性最佳pH值异常低，为5.5。在全细胞中，当小肠结肠炎耶尔森氏菌的培养基值降至pH 3.0以下，摩根氏摩根菌的培养基值降至pH 5.5以下时，激活发生，这表明体内激活是细胞质酸化的结果。对摩根氏摩根菌脲基因座部分的DNA序列分析表明，该酶结构亚基的预测一级结构与小肠结肠炎耶尔森氏菌脲酶的最为相似。这两种脲酶在活性位点附近的一个相似区域与大多数其他脲酶不同，但存在于发酵乳杆菌的脲酶中。这个相似区域可能是小肠结肠炎耶尔森氏菌和摩根氏摩根菌脲酶独特性质的原因，因为发酵乳杆菌脲酶的活性也已被证明具有低pH最佳值。
