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The beast and its Achilles heel:
A novel target to fight multi-resistant pathogenic bacteria
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Our project:
Our project is aimed at the development of a simple screening system, which allows the rapid identification and characterization of substances that disturb c-di-AMP homeostasis in pathogenic bacteria.
The principle of how such a screening system could look like is illustrated in Figure 1. The screening system will be established in the non-pathogenic bacterium E. coli.
First, we want to construct a promoter-reporter gene fusion which allows us to monitor the activity of a transcription factor that only binds to a specific DNA sequence (operator) in the presence of c-di-AMP. The operator sequence will be placed between a constitutively active promoter and a reporter gene, such as lacZ and gfp encoding the -galactosidase and the green-fluorescent protein (GFP), respectively.
The activity of either of the two proteins is very easy to detect. Then, we will evaluate whether binding of the transcription factor and thus inhibition of the promoter-reporter gene fusion can be controlled by exogenous c-di-AMP.
Finally, we want to express a diadenylate cyclase from B. subtilis to inhibit the promoter reporter gene fusion by endogenously synthesized c-di-AMP. There are two big advantages of using E. coli as a host for the development of a screening system to identify antibacterial compounds that interfere with c-di-AMP homoeostasis in Gram-positive pathogenic bacteria.
First, c-di-AMP is not synthesized in E. coli. Thus, compounds that inhibit c-di-AMP synthesis will specifically inhibit growth of Gram-positive bacteria. Second, the use of a nonpathogenic E. coli strain, which is easy to cultivate will keep the costs very low.
We are confident that our screening system will facilitate the identification of novel antibacterial substances because any change in the activity of the c-di-AMP-dependent promoter-reporter gene fusion, either by inhibition of c-di-AMP synthesis or by activation of DNA-binding activity of the transcription factor will indicate perturbation of c-di-AMP homeostasis.
