Louis Cortes
Department of applied engineering physics, Lambert Lab, Cornell University, Ithaca, New York
https://www.louiscortes.science/
The physics of gene regulation in bacteria: new insights from single cell dynamics of the lac operon
In favourable conditions, bacteria undergo exponential growth by duplicating their genomic DNA (deoxyribonucleic acid) and translating genes into proteins, which carry out essential biological functions. The regulation of gene expression is vital for cell functionality, adaptation, and survival. A classic example of gene expression in bacteria is the lac operon, a gene network responsible for lactose metabolism and uptake. Due to its well-studied nature and relative simplicity, the lac operon continues to serve as a model system for developing quantitative theories on gene regulation.
This presentation introduces fundamental concepts and quantitative models relevant to the physics of the lac operon, focusing first on repression and induction. Repression involves the lac repressor binding near the lac promoter region to prevent expression, while induction describes how allosteric inducer molecules can release the repressor, allowing gene expression. We explain how this mechanisms, coupled with active feedback, create an all-or-none switch behaviour. The switching is further introduced in the light of recent work emphasising the role of stochasticity.
In the remainder of the talk, we present video-microscopy experiments monitoring the dynamics of the lac operon in bacteria trapped in a microfluidic chemostat. Engineered strains of bacteria with overexpressed lac repressor are used, and the dynamics are tracked with a reporter protein controlled by the lac repressor. Calibration of the system aligns well with prior work, suggesting a slightly different repression mechanism. As anticipated, stochastic switching is observed, and switching rates follow expected trends. Interestingly, our findings indicate that growth conditions can influence the nature of the switch in our system.