Collective membrane potential dynamics in bacterial colonies

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Structured populations of Bacillus subtilis coordinate their metabolism by electrical communication. Currently, it is unknown, whether other bacterial species synchronize their electrochemical behavior. We found that within spherical colonies formed by Neisseria gonorrhoeae, bacteria hyperpolarize at the center and subsequently, a shell of hyperpolarized cells travels radially towards the periphery of the colony. This hyperpolarization is followed by depolarization at the colony center. In this proposal, we aim at discovering triggers for hyperpolarization, the mechanism of collective propagation of hyperpolarization, and its relation to growth arrest and related consequences on population fitness. Specifically, we will correlate growth arrest at the colony center with membrane potential. To this end, we will combine our recently established method for characterizing the growth rate with spatio-temporal resolution with tools for characterizing the membrane potential. Then, we aim at investigating two putative triggers of hyperpolarization. We will assess whether depletion of oxygen or a nutrient causes hyperpolarization. Furthermore, we will test the hypothesis that build-up of mechanical pressure at the center of the colony limits growth and causes hyperpolarization. We will vary the pressure by tuning the attractive force between gonococci in the colony. Attractive forces will be tuned by genetically modifying type 4 pili and characterized by laser tweezers. Finally, we will address the question whether cell-to-cell communication is required for the propagation of hyperpolarization. To this end, we will investigate the spatio-temporal dynamics of the hyperpolarization wave in different colony structures. In the long term, it will be important to identify the ion channels responsible for hyperpolarization and to address the fitness effects of collective changes in membrane potential.