Biophysics & Development Seminar: Kerwyn C. Huang, Stanford University

Presenter:
Kerwyn C. Huang, Ph.D.
Professor of Bioengineering and of Microbiology and Immunology
Stanford University

Title: Biophysics of bacterial cell growth and evolution

Abstract: Bacterial cells constantly face complex environmental changes in their natural habitats. While steady-state cell size correlates with nutrient-determined growth rate, it remains unclear how cells regulate their morphology during rapid environmental changes. We quantified cellular dimensions throughout passage cycles of stationary-phase cells diluted into fresh medium and grown back to saturation and found that cells exhibited characteristic dynamics in surface area to volume ratio (SA/V). SA/V dynamics were conserved across many genetic/chemical perturbations, as well as across species and growth temperatures. We developed a model with a single fitting parameter, the time delay between surface and volume synthesis, that quantitatively explains our SA/V observations and showed that this time delay was indeed due to differential expression of volume and surface-related genes. The first division after dilution occurred at a tightly controlled SA/V, a previously unrecognized size-control mechanism highlighting the relevance of SA/V. Finally, our time-delay model successfully predicted the quantitative changes in SA/V dynamics due to altered surface area synthesis rates or time delays from translation inhibition. Our minimal model thus provides insight into how rod-shaped cells regulate their morphologies through differential regulation of surface area and volume synthesis and potentiates deep understanding of the connections between growth rate and cell shape in dynamic environments. Time permitting, I will also discuss our efforts to dissect selection and transmission in animal models using barcoded bacterial strains.