AN ESCHERICHIA-COLI CHROMOSOMAL ARS OPERON HOMOLOG IS FUNCTIONAL IN ARSENIC DETOXIFICATION AND IS CONSERVED IN GRAM-NEGATIVE BACTERIA
AN ESCHERICHIA-COLI CHROMOSOMAL ARS OPERON HOMOLOG IS FUNCTIONAL IN ARSENIC DETOXIFICATION AND IS CONSERVED IN GRAM-NEGATIVE BACTERIA
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DOI：
10.1128/jb.177.8.2050-2056.1995
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发表时间：
1995-04-01
影响因子：
3.2
通讯作者：
DUBOW, MS
中科院分区：
文献类型：
--
作者：
DIORIO, C;CAI, J;DUBOW, MS
砷是一种有毒的类金属，其三价和五价离子能抑制许多生物化学过程。在革兰氏阳性菌和革兰氏阴性菌的多拷贝质粒中都发现了编码砷抗性的操纵子，抗性机制由单个操纵子编码，该操纵子通常由调节砷酸盐还原酶和内膜相关的亚砷酸盐输出系统的表达的亚砷酸盐离子诱导的阻遏物组成。使用lacZ转录基因融合库，我们已经确定了大肠杆菌操纵子，其表达诱导细胞暴露于浓度低至5微克/升的亚砷酸钠。该染色体操纵子被克隆，测序，并发现由三个顺反子，我们命名为arsR，arsB和arsC，因为它们的强同源性质粒携带的ars操纵子。发现染色体ars操纵子中的突变体对砷酸钠和亚砷酸盐暴露的敏感性比野生型大肠杆菌高约10至100倍。coli，而野生型E.发现含有克隆在ColE 1质粒上的操纵子的大肠杆菌对砷酸钠和亚砷酸盐的抗性至少高2到10倍。此外，Southern印迹和高严格性杂交，这操纵子与染色体DNA从一些细菌物种之间的家庭肠杆菌科的成员显示同源序列，杂交是可检测的，即使在铜绿假单胞菌。这些结果表明，染色体ars操纵子可能是质粒携带的操纵子的进化前体，因为多拷贝质粒位置将允许操纵子被扩增，其产物赋予对这种有毒类金属的抗性增加。
Arsenic is a known toxic metalloid, whose trivalent and pentavalent ions can inhibit many biochemical processes. Operons which encode arsenic resistance have been found in multicopy plasmids from both gram-positive and gram-negative bacteria, The resistance mechanism is encoded from a single operon which typically consists of an arsenite ion-inducible repressor that regulates expression of an arsenate reductase and inner membrane-associated arsenite export system. Using a lacZ transcriptional gene fusion library, we have identified an Escherichia coli operon whose expression is induced by cellular exposure to sodium arsenite at concentrations as low as 5 mu g/liter. This chromosomal operon was cloned, sequenced, and found to consist of three cistrons which we named arsR, arsB, and arsC because of their strong homology to plasmid-borne ars operons. Mutants in the chromosomal ars operon were found to be approximately 10- to 100-fold more sensitive to sodium arsenate and arsenite exposure than wild-type E. coli, while wild-type E. coli that contained the operon cloned on a ColE1-based plasmid was found to be at least 2 - to 10-fold more resistant to sodium arsenate and arsenite. Moreover, Southern blotting and high-stringency hybridization of this operon with chromosomal DNAs from a number of bacterial species showed homologous sequences among members of the family Enterobacteriaceae, and hybridization was detectable even in Pseudomonas aeruginosa. These results suggest that the chromosomal ars operon may be the evolutionary precursor of the plasmid-borne operon, as a multicopy plasmid location would allow the operon to be amplified and its products to confer increased resistance to this toxic metalloid.