2024
Context:
The membrane potential of living cells is a key element in the exchanges and communication between cells. It is essential in excitable cells such as neurons and contractile cells. However, its role in bacteria has only recently been investigated (see review by Benarroch and Asally, 2020). It has been implicated in cell division, bacterial movement, antibiotic resistance and possibly bacterial communication. Spontaneous variations in potential have been observed in isolated bacteria (Kralj et al., 2011), but this phenomenon is not well understood. In the laboratory, we have shown that these oscillations are linked to the physiological state of the bacteria and the stress they are undergoing.
In nature, bacteria mainly exist in the form of biofilms or microcolonies. Within these structures, they can acquire new properties. In particular, it has been shown that depolarisation waves involving potassium channels can occur inside a biofilm (Prindle et al., 2015). More recently, a hyperpolarisation wave has been observed in Neisseria gonorrhoeae colonies, starting from the center of the colony and propagating to its edges (Hennes et al., 2023). These observations therefore suggest the existence of cooperative phenomena involving the membrane potential.
Internship topic: We want to gain a better understanding of the dynamics of membrane potential in bacterial colonies, and in particular how their physical environment can affect it. We will use the bacteria Neisseria gonorrhoeae. The microcolonies will be formed in a more or less concentrated agar gel in order to control the physical constraints and rigidity of the medium. The addition of fluorescent probes (ThT, TMRM) will be used to monitor variations in potential across the colony. The idea is to link a physiological parameter representative of the colony to the physical/mechanical parameters of its environment. Mutants of pili, the structures involved in the transmission of mechanical forces within colonies, will also be used.
This work will involve microbiological experiments for bacterial culture, fluorescence microscopy to monitor membrane potential and image analysis. It is therefore aimed at a candidate with a Masters 2 degree at the interface between physics or physical chemistry and biology. However, a candidate with a strong motivation for interdisciplinarity will also be considered favorably.
The traineeship will be possibly followed by a PhD thesis.
Contact : frederic.joubert@sorbonne-universite.fr
Bibliographie :
Kralj et al., Science, Vol 333, 2011
Prindle et al., Nature, Vol 527, 2015
Benarroch and Asally, Trends in Microbiology, Vol 28(4), 2020
Hennes et al., Plos Biology, Vol 21(1), 2023