Foster J W, Bearson B
Department of Microbiology and Immunology, College of Medicine, University of South Alabama, Mobile 36688.
J Bacteriol. 1994 May;176(9):2596-602. doi: 10.1128/jb.176.9.2596-2602.1994.
Salmonella typhimurium exhibits a low-pH-inducible acid tolerance response (ATR) that can protect the adapted cell from severe acid challenge (pH 3.3). It is a two-stage system, with some proteins induced at pH 5.8 (pre-acid shock) and others induced below pH 4.5 (acid shock). The genetics of acid resistance was investigated through the use of a new screening medium. The medium contained 200 microM dinitrophenol (DNP) and was adjusted to pH 4.7 to 4.8. The medium will lower the internal pH of cells to a lethal level. However, cells capable of mounting an ATR will survive longer on this medium than acid-intolerant cells. Using this DNP lethal screening strategy, we isolated several acid-sensitive insertion mutants. Some mutants were defective in the pre-acid shock ATR stage but exhibited a normal or nearly normal post-acid shock-induced acid tolerance (atrB and atrC). Others could not induce acid tolerance by using either pre- or post-acid shock strategies (atrD, atrF, and atrG). The atrB locus was found to be part of a regulon under the control of a trans-acting regulator, atbR. An insertion in atbR caused constitutive acid tolerance because of overexpression of the regulon. Mutations in atrD and atrF affected iron metabolism and, in a manner analogous to ferric uptake regulator (fur) mutations, diminished acid resistance. The atrF mutation mapped within the ent cluster, probably in a fep uptake locus. The atrD locus mapped near metC and may represent an insertion into the S. typhimurium homolog of the Escherichia coli exbB or exbD locus. The mutation in atrC caused extreme UV light sensitivity and proved to occur within the polA (DNA polymerase I) locus. The results support the concept of overlapping acid protection systems in S. typhimurium.
鼠伤寒沙门氏菌表现出一种低pH诱导的酸耐受反应（ATR），该反应可保护适应后的细胞免受严重酸胁迫（pH 3.3）。这是一个两阶段系统，一些蛋白质在pH 5.8（酸前休克）时被诱导，而其他蛋白质在pH 4.5以下（酸休克）时被诱导。通过使用一种新的筛选培养基研究了抗酸遗传学。该培养基含有200微摩尔二硝基苯酚（DNP），并将pH值调节至4.7至4.8。该培养基会将细胞内pH值降低至致死水平。然而，能够产生ATR的细胞在这种培养基上比不耐酸的细胞存活时间更长。使用这种DNP致死筛选策略，我们分离出了几个酸敏感插入突变体。一些突变体在酸前休克ATR阶段存在缺陷，但在酸休克后诱导的酸耐受方面表现正常或接近正常（atrB和atrC）。其他突变体则无法通过酸前或酸后休克策略诱导酸耐受（atrD、atrF和atrG）。发现atrB基因座是一个受反式作用调节因子atbR控制的调节子的一部分。atbR中的插入由于调节子的过表达而导致组成型酸耐受。atrD和atrF中的突变影响铁代谢，并且以类似于铁摄取调节因子（fur）突变的方式降低了酸抗性。atrF突变位于ent簇内，可能在一个fep摄取基因座中。atrD基因座位于metC附近，可能代表插入到鼠伤寒沙门氏菌中大肠杆菌exbB或exbD基因座的同源物中。atrC中的突变导致对紫外线极度敏感，并且被证明发生在polA（DNA聚合酶I）基因座内。这些结果支持了鼠伤寒沙门氏菌中重叠酸保护系统的概念。
