We published a new paper (link) showing that the material properties of dead cells impacts microbial social interactions.

How do antagonistic bacteria coexist in crowded biofilms? Most contact killing studies focus on cellular and sub-cellular events over short time scales, showing that the abundance of ‘target’ cells (i.e., cells that are susceptible to attack) can rapidly decrease. These observations reinforce the idea that contact killing is a highly potent antagonistic strategy. Thus, for killer and target cells to coexist, the current assumption is that target cells must possess strain-specific, genetically controlled defense mechanisms. However, we found that physical consequences of cell death prevent further lethal attacks from occurring. Dead cell debris accumulates at the interfaces between killer and target cells, contact a physical barrier. The barrier separates killer and target cells, preventing contact and thus preventing contact killing. Our results indicate that while very effective at reducing the population of competing cells on first contact, contact killing can actually help antagonistic bacteria coexist.

We have a new paper in eLife (link) in which we show that specialization may evolve more readily than previously thought.

The single most important benefit of multicellularity is the fact that organisms can evolve specialized cell types (i.e., being a brain or skin cell), but we know little about how specialization first evolved. It has long been assumed that specialization will evolve only if there is an accelerating, or convex, return on investment; for example, if twice the investment in a given task produces four times the yield. We have been studying the role of group structure in the evolution of specialization, using a minimal individual-based model. Surprisingly, we found that for a broad class of sparsely connected structures, specialization evolves even with saturating, or concave, returns on investment. Sparsely connected groups are able to connect many complementary specialists, which increases the benefit of specialization, without also connecting many like-specialists, which decreases the value of specialization. Our results remove a significant barrier to the evolution of specialization – the existence of accelerating returns on investment – and thus suggest that the evolution of specialization is even more favorable than previously thought

What do hacked connected cars have in common with biophysics and soft matter? Active and emergent phenomena! In a collaboration with Jesse Silverberg of Multiscale Systems, Inc., we find that the consequences of a large scale hack of connected cars could be dire – but are predicted through an extension of percolation theory! Paper here, and summary in Physics here.

Check out our new paper on the mechanics of hierarchical structures – and its relevance for evolution – published today in PNAS.

Also, a great write-up is available here.

In our previous paper on the evolution of multicellularity, we showed that mechanical stresses develop during growth, eventually fracture clusters of cells into two pieces. Now we ask: when faced with this mechanical challenge, what is the best way to evolve large size? In our new paper, selected as a Rapid Communication in PRE, we show increasing bond strength does little, but modify how cells pack does a lot!

Our new paper in PRL investigates an effective fluctuation response relationship in biofilms featuring death and reproduction. The fluctuation-dissipation theorem, derived by Harry Nyquist in the 1920’s, is essential to our understanding of equilibrium solids. The relationship between thermal fluctuations and mechanical responses provided a framework through which mechanical properties of solids were measurable and predictable. Our paper. The same may be possible for living films; we investigated it in collaboration with the Hammer lab, here  at Georgia Tech’s School of Biological Sciences. Our work builds on a beautiful paper from Risler, Peilloux, and Proust, which investigated a model of apoptosis and reproduction in tissues.

What do nascent multicellular organisms and colloidal particles have in common? Packing matters! Check out our new Nature Physics paper to learn more! Also, be sure to read the fantastic News&Views article on this work by Vernita Gordon!

Our new preprint investigates how coffee-ring-effect produces gradients in cell-density when a drop of liquid culture is dried. These initial conditions have a large impact on the subsequent competition between strains, and can even switch which strain wins. Thus, the coffee-ring effect may ultimately impact evolutionary outcomes.

Dhaivat Mehta was one of the grand award winners at this year’s Georgia Science & Engineering Fair! He has been working with us on his project “Modeling T6ss-Mediated Killing in Microbial Colonies.”

Check out our paper on a different form of active matter, whose activity is not due to mobility, but to death and reproduction! Published this week in Nature Communications, this interdisciplinary paper brought together classic physics, microbiology, ecology and more!