Temperature regulation of the heme transport system in Escherichia coli
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Temperature regulation of the heme transport system is important, as it allows the microorganism to sense that it has entered the mammalian host environment of 37° C and adjust the expression of its iron-transport and virulence genes accordingly. It is known that expression of shuA, a gene encoding the outer membrane receptor that binds heme, is regulated by the amount of iron in the environment, yet little is known about the role of temperature in the regulation of this system. To study the effect of temperature on the activity of the shuA promoter, E. coli was transformed with a plasmid containing the shuA promoter fused to the reporter gene lacZ and transformed cultures were assayed for ß-galactosidase activity as an indirect measure of shuA promoter activity. Results suggest that shuA promoter activity is temperature regulated, with increased activity at 37° C compared to 30° C. The histone-like nucleoid structuring protein (H-NS) is a global regulator in E. coli, and it has been shown to respond to environmental signals, including osmolarity, temperature, and pH. To test the hypothesis that H-NS is mediating shuA promoter activity, gene expression was measured in an hns mutant and wild-type strain. Results indicate that H-NS is partially, but not solely, responsible for the temperature regulation of shuA. In a separate investigation, the possibility of exploiting the presence of heme transport systems in pathogenic bacteria to deliver toxic compounds to the pathogen was tested. The toxicity of MGd and MGd-18-crown-6 texaphyrin compounds to E. coli expressing the heme transport system was examined. Results suggest that texaphyrin compounds are not toxic to E. coli growth.