Marine snow, organic solute plumes, and optimal chemosensory behavior of bacteria

Leaking organic solutes form an elongated plume in the wake of a sinking ag gregate. These solutes may both be assimilated by suspended bacteria and gu ide bacteria with chemokinetic swimming behavior toward the aggregate. We u sed modifications of previously published models of the flow and concentrat ion fields around sinking aggregates and of chemokinetic behavior of bacter ia to identify the behavior that optimizes aggregate colonization and plume utilization. The optimal solution is governed by physical constraints and is a trade off between a high sensitivity to chemical signals and a long si gnal integration time. For a run-and-tumble swimming behavior, the predicte d tumbling frequency is between 1 and 10 s(-1), similar to that reported fo r marine bacteria. The predicted optimal sensitivity to chemical signals is similar to or greater than that known for Escherichia coli. The optimal be havior was used to examine the potential contribution of aggregate-generate d solute plumes for water column bacteria] production. Despite occupying on ly a small volume fraction, the plumes may provide important growth habitat s for free bacteria and account for a significant proportion of water colum n bacterial production at typical concentrations of marine snow aggregates.