Dr. Tom Day
Postdoctoral Fellow, USC Marine & Environmental Biology

Transiently Multicellular Marine Bacteria:
Linking Patch Dynamics to Microbial Ecology

Tuesday, January 21
11:30 AM
AHF 153 (Torrey Webb Room)

Abstract: Bacteria often form transiently multicellular structures such as biofilms and fruiting bodies, which play important roles in ecological processes. For example, in marine environments with patchy resources, aggregates of heterotrophic bacteria clump into multicellular groups of microbial activity, where they cycle organic carbon into carbon dioxide or convert it into living biomass. In such a system, we can consider there to be both patches of resources and patches of bacteria. Yet, understanding how emergent multicellular states shape and interact with the ecology of a patchy marine environment remains an outstanding challenge in marine microbial ecology. One important factor that is altered by bacteria clumping into large groups is the rate at which they encounter particulate debris, nutrients, viruses, and each other. Here, we combine experiments leveraging the model marine bacterium Vibrio splendidus with empirical models to characterize how geometric encounters between various patches (both resources and bacterial aggregates) scale and fluctuate with patch sizes, concentrations, and fluid properties. We find that bacterial aggregates can become large enough to approach finite-inertia regimes of fluid flow, meaning that empirical encounter rate scaling relationships can differ from predicted scaling derived from zero-inertia considerations. We further find that when nutrients are scarce, the size of multicellular structures is inversely related to both the mean and variance of the per-capita cell-resource encounter rate. Thus, while encountering resources more consistently, cells in large multicellular aggregates receive less resource per capita. This suggests a trade-off between the consistency with which bacteria encounter resources, and the maximum amount of resource per capita. We explore the conditions under which this tradeoff may lead to coexisting ‘strategies’ through which bacteria forage for resources. Altogether, we indicate ways in which the landscape of particle encounters may inform a fitness landscape, thus connecting marine biophysical processes to broader ecological dynamics.