16 June 2023
Srividya Iyer-Biswas
Department of Physics
Purdue University
Homeostasis — the holding "constant" of key physiological variables — is so important a phenomenon as to be considered an organizational principle in physiology. Yet, despite being of outstanding interest, what mathematical frameworks govern the best-studied homeostatic state variables — cell size — of the simplest organism — a bacterial cell — has remained controversial. In this talk I will highlight our effort to address this gap by reconceptualizing homeostasis from an inherently stochastic, intergenerational perspective. We have charted organismal biographies precisely via high-precision dynamic experiments using our SChemostat technology. I will first show how we established that individual cells indeed maintain homeostasis of their characteristic sizes! Next, the organizational principles extracted from these data: an intergenerational scaling law and other "emergent simplicities", which facilitate a principled route to dimensional reduction of the problem. Then the definitive theory of intergenerational homeostasis of individual bacterial cells by using the observed emergent simplicities as essential building blocks. By fitting parameter-free data for multiple organisms to the theory, we establish that the framework indeed is the apposite one for capturing the basic systems physics of stochastic homeostasis. Finally, we show the extension to time-varying growth conditions, new emergent simplicities, and the generalization to stochastic intergenerational allostasis of the instantaneous single-cell growth rate.