Jiggling genes and dancing bacteria: two problems in biologically-inspired hydrodynamics
Michael Graham
Department of Chemical and Biological Engineering
University of Wisconsin-Madison
Abstract:
Emerging micro- and nanofluidic approaches to single molecule analysis of genomic DNA have fueled considerable interest in the structure and dynamics of solutions of long-chain polymers in confined geometries. In the first part of this talk we describe simulation, theory and experimental studies of the hydrodynamics of solutions of long DNA molecules in microchannels. A key feature of this problem is the cross-stream migration of the large molecules—migration has been widely observed in polymer solutions but heretofore poorly understood. We elucidate the various mechanisms that drive migration: the dominant effect arises from the fluid motion induced by a DNA molecule as it tumbles around in the flow, and cannot be captured if the hydrodynamic effects of confinement are ignored.
The second part of this talk describes very recent work motivated by observations that populations of swimming bacteria exhibit a fascinating variety of flow phenomena, whose mechanisms are not understood. We propose a simple model of a swimming organism that is amenable to direct simulations of large populations, and show that cases exist in which the swimming motion generates dramatically enhanced transport in the fluid. This transport is coupled to the existence of long-range correlations of the fluid motion. Furthermore, the mode of swimming matters in a qualitative way: microorganisms pushed from behind by their flagella are predicted to exhibit enhanced transport and long-range correlations, while those pulled from the front are not. Thus these two classes of swimmers have very different effects on the transport of nutrients or chemoattractants in their environment; this observation may be related to the evolution of different modes of swimming.