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Cyclic nucleotide signalling in the human pathogen Listeria monocytogenes

Periodic Reporting for period 1 - a-Sign (Cyclic nucleotide signalling in the human pathogen Listeria monocytogenes)

Reporting period: 2016-05-01 to 2018-04-30

a-Sign looks into how bacteria use intracellular signals to sense and adapt to their surroundings. It focuses on small molecules called cyclic nucleotides, which can play a role in relaying information to change a bacterium's behavior upon sensing of different stimuli.

The bacterium used in this study was Listeria monocytogenes, one of the most virulent foodborne pathogens, causing febrile gastroenteritis and listeriosis, and affecting pregnant women, newborns, immunocompromised individuals, and the elderly.

To understand how L. monocytogenes survives to the environment is important because the population of the Western countries is ageing and the elderly are a risk group. Since 2012, the number of listeriosis cases has been in constant increase.

In this project, the cyclic nucleotides (cAMP, cGMP, c-di-AMP and c-di-GMP) and their regulatory function (including virulence and antimicrobial resistance), were investigated.
The project was to investigate the presence of cAMP and cGMP in extracts of L. monocytogenes and screened a collection of deletion mutants in two-component systems to look for strains with an altered cyclic nucleotide profile.

It was observed that L. monocytogenes extracts have cAMP levels similar to those in Escherichia coli extracts. The cAMP molecule was detected in bacteria grown aerobically in rich or chemically defined medium, and levels were higher in exponential phase than in stationary phase. The cGMP molecule was detected but levels were considered residual.

In the screen, four deletion mutants were found to have an altered cyclic nucleotide profile. One of them displayed low levels of c-di-GMP and was associated with a higher tolerance to ethanol, higher sensitivity to ampicillin and hypervirulent phenotype.

The results of this project were presented at a Gordon Conference in the USA (as oral and poster presentations), the i3S post-doc seminar, and the i3S annual meting. My topic of research was also presented in 3 schools, to a total of 150 pupils aged 13-17. A manuscript for publication in a peer-reviewed international journal is in preparation.
At the start of the project it was known that L. monocytogenes uses c-di-AMP and c-di-GMP signalling networks to control various biological functions. This work laid the first stepping-stone to the study of cAMP signalling in L. monocytogenes. In addition, it identified five new putative cyclic nucleotide dependent signalling cascades, some of which seem to be responsible to control tolerance to cell envelope-related stresses. Further investigations may allow us to understand better processes such as antibiotic resistance and L. monocytogenes pathogenesis and, eventually, find new targets for drug development.

By bringing expertise acquired at other institutions/countries to i3S and designing my own project, I introduced a new line of research in the group of Dr Didier Cabanes and I set up a new technique in the lab. Peers in the lab and from a neighbouring group were able to take advantage of this technique and, reciprocally, I was able to gain new expertise from them.

I supervised three BSc students who developed their final year reports based on work from this project, and therefore concluded their first higher education degree. I continued managing and promoting school visits implemented by Native Scientist and I attended two international conferences.

Finally, during the time of this project I was elected Post-doc representative of the host institution, which meant that I have actively engaged with my peers, participated in executive meetings, organised three events on career development and designed a strategy to raise funds for science in society.
Overview of the Project Aims