패혈증 비브리오균에서 aerobactin 수용체 단백을 암호화하는 iutA 유전자의 발현 조절

Abstract

Regulatory Mechanism of the iutA Gene Encoding Aerobactin Receptor Protein in Vibrio vulnificus

The ferrophilic bacterium Vibrio vulnificus can utilize the siderophore aerobactin of Escherichia coli for iron acquisition via the specific receptor IutA. This siderophore piracy by V. vulnificus may contribute to its survival and proliferation, especially in mixed bacterial environments. This study was undertaken to determine the effects of glucose/Crp (cAMP-receptor protein), aerobactin/IutR (Gnt-like repressor) and iron/Fur (ferric uptake regulator) on iutA expression, and to detail the roles of Crp, IutR and Fur in the regulation of iutA expression under iron-deficient (ID) and iron-sufficient (IS) conditions. An in frame deletion mutation in crp severely repressed iutA expression under moderately ID conditions, and this change was recovered by in trans complementing wild-type crp. Under severely ID conditions, iutA expression was induced even in the absence of Crp, and iron increased iutA expression in the presence of Crp but repressed it in the absence of Crp. The presence of aerobactin increased iutA expression under moderately ID conditions. An in frame deletion mutation in fur de-repressed iron-repressible iutA expression under IS conditions, and this change was recovered by in trans complementing wild-type fur. Iron repressed iutA expression under moderately ID and IS conditions only in the presence of Fur but de-repressed it in the absence of Fur. Glucose repressed iutA expression under moderately ID conditions in the presence of Fur, but not in the absence of Fur. Aerobactin induced iutA expression under both ID and IS conditions and regardless of the absence or presence of Crp or Fur. These results indicate that (i) Crp is not essential for constitutional iutA expression, but is required to optimally induce iutA expression in response to glucose deprivation regardless of iron or aerobactin availability, (ii) IutR is not essential for iutA repression, but responds to aerobactin availability regardless of iron or glucose levels, (iii) Fur functions as a repressor of iutA expression in proportion to iron levels. Taken together, iutA expression is likely to be under the independent but cooperative control of Crp, IutR and Fur.