Institute for the Physics of Living Systems


IPLS Seminar - Prof. Suckjoon Jun (University of California)

15 April 2019, 11:00 am–12:00 pm

Suckjoon Jun

Title: Mechanistic origin of cell-size control and homeostasis in bacteria

Event Information

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2nd Floor Seminar Room (2.30), LMCB
MRC Building
Gower Street

Abstract: Evolutionarily divergent bacteria share a common phenomenological strategy for cell-size homeostasis under steady-state conditions. In the presence of inherent physiological stochasticity, cells following this recently (re)discovered “adder” principle gradually return to their steady-state size by adding a constant volume between birth and division regardless of their size at birth. However, the mechanism of the adder has been unknown despite intense efforts. Based on our new data and modeling, I will explain that the adder is a direct consequence of two general processes in biology: (1) threshold -- accumulation of initiators and precursors required for cell division to a respective fixed number, and (2) balanced biosynthesis -- maintenance of their production proportional to volume growth. This mechanism is naturally robust to static growth inhibition, but also allows us to “reprogram” cell-size homeostasis in a quantitatively predictive manner in both Gram-negative Escherichia coli and Gram-positive Bacillus subtilis. By generating dynamic oscillations in the concentration of the division protein FtsZ, we were able to oscillate cell size at division and systematically break the adder. In contrast, periodic induction of replication initiator protein DnaA caused oscillations in cell size at initiation, but did not alter division size or the adder. Finally, we were able to restore the adder phenotype in slow growing E. coli, the only known steady-state growth condition wherein E. coli significantly deviates from the adder, by repressing active degradation of division proteins. Together these results show that division and replication are independently controlled, and that division processes exclusively drive cell-size homeostasis in bacteria.

About the Speaker

Prof. Suckjoon Jun

at University of California, San Diego

More about Prof. Suckjoon Jun