Describing Myxococcus xanthus Aggregation Using Ostwald Ripening Equations for Thin Liquid Films

Abstract

When starved, a swarm of millions of Myxococcus xanthus cells coordinate their movement from outward swarming to inward coalescence. The cells then execute a synchronous program of multicellular development, arranging themselves into dome shaped aggregates. Over the course of development, about half of the initial aggregates disappear, while others persist and mature into fruiting bodies. This work seeks to develop a quantitative model for aggregation that accurately simulates which will disappear and which will persist. We analyzed time-lapse movies of M. xanthus development, modeled aggregation using the equations that describe Ostwald ripening of droplets in thin liquid films, and predicted the disappearance and persistence of aggregates with an average accuracy of 85%. We then experimentally validated a prediction that is fundamental to this model by tracking individual fluorescent cells as they moved between aggregates and demonstrating that cell movement towards and away from aggregates correlates with aggregate disappearance. Describing development through this model may limit the number and type of molecular genetic signals needed to complete M. xanthus development, and it provides numerous additional testable predictions.

Plastic multicellular development ofMyxococcus xanthus: genotype-environment interactions in a physical gradient

“…To our knowledge, mechanisms behind this organizational level have not been explored, although, it is known that mechanical forces and living matter interact in a bidirectional way giving rise to robust patterns [7,8]. Based in our results and taking into consideration both the influence of substrate fibers in colony formation [12] and the surfacetension driven coarsening process of aggregation [23], we can suggest that the mechanical properties of the medium constitute a key element when thinking about environment at the microscale.…”

Interplay of mesoscale physics and agent-like behaviors in the parallel evolution of aggregative multicellularity

“…During predation, cells align and move concertedly into ripple-like traveling waves [62]. Once development has started, M. xanthus aggregation is largely driven by entropy minimization through reduction of the surface area on which the collective cell population contacts the substratum [63]. This is a comparable behavior to that of liquid droplets, where individual subunits or clusters move into larger droplets of larger volume but smaller contact area with the surface.…”

An Evo‐Devo Perspective on Multicellular Development of Myxobacteria

“…During aggregative development, motion and organization of individual cells are affected by different physicochemical aspects such as medium viscosity, cell–medium adhesion, diffusion of intercellular signals, and hydrodynamic forces (Persat et al., ). In fact, the movement of myxobacteria during the aggregation stage has been empirically compared to the behavior of liquids in a thin layer, following the so‐called Ostwald dynamics (Bahar et al., ). Under these dynamics, particles, and arguably aggregating cells, tend to minimize the surface area contacting the media by reducing the number of aggregates and increasing the aggregate volume.…”

“…Under these dynamics, particles, and arguably aggregating cells, tend to minimize the surface area contacting the media by reducing the number of aggregates and increasing the aggregate volume. With this in mind, Bahar and collaborators () were able to predict the position and fate of nascent aggregates during the early stages of M. xanthus development. However, this model fails to predict the collective dynamics for later stages possibly due to the fact that their study did not consider changes occurring as a consequence of development, like cell differentiation.…”