Abstract:

Viruses that infect bacteria—known as phages—are the most numerous biological entities on Earth, yet their success depends not only on molecular strategies but also on where and when they encounter their hosts. In this seminar, I will show how spatial structure and chance events strongly influence the dynamics of phage–bacteria ecosystems.
In the first part, we show through modelling that local viral attacks on bacterial aggregates can trigger dramatic boom–bust cycles while simultaneously suppressing global predator–prey oscillations, leading to self-organized patterns with aggregate sizes following a power-law distribution [1].
In the second part, we consider systems where bacteria expand by consuming nutrients, thereby creating nutrient gradients and biasing their motion up those gradients (chemotaxis). This process generates advancing growth fronts. Previous experiments revealed complex local collapse patterns when phages were introduced into such systems [2]. Our model addresses the regime in which bacterial chemotactic expansion outpaces phage diffusion, and shows how rare and stochastic events—in which a few infected cells reach the front, burst, and release new phages—can account for key features of the experimentally observed patterns [3].
Together, these results emphasize that microbial ecosystems cannot be understood without accounting for spatial structure and stochasticity.
 
[1] Yadav A, Mitarai N, Sneppen K. Self-organized coexistence of phage and a population of host colonies. Physical Review Letters. 2025 Mar 28;134(12):128402.
[2] Ping D, Wang T, Fraebel DT, Maslov S, Sneppen K, Kuehn S. Hitchhiking, collapse, and contingency in phage infections of migrating bacterial populations. The ISME Journal. 2020 Aug;14(8):2007-18.
[3] Bergamaschi L and Mitarai N, manuscript in preparation.

Speaker: Dr. Namiko Mitarai (Niels Bohr Institute, Univ. of Copenhagen)
 

 
Host: Tetsuhiro Hatakeyama, ELSI.

Date: Wed. 1 Oct 16:00-17:00 JST

Venue: Mishima Hall, ELSI (hybrid)