Bio uiddynamics of Lubricating Bacteria

Various bacterial strains exhibit colonial branching patterns during growth on thin poor substrates. The growth can be either diiusion-limited or kinetic-limited, according to the imposed growth conditions. We present experimental observations of patterns exhibited by the bacterial strains Paenibacillus dendritiformis and Paenibacillus vortex. All manners of branching patterns are observed, the three main being: 1) basic branching; 2)chiral branching; 3) vortex branching. We show that the following biological features can explain the spectrum of observed patterns: 1. Formation of a lubricating uid. 2. Food chemotaxis. 3. Attractive and repulsive chemotaxis signaling. 4. Flagella handed-ness. 5. Transition into pre-spore state. In the theoretical studies we employ knowledge drawn from branching patterning in non-living systems and the mathematical properties of reaction-diiusion models and atomistic models. The above can be used not just to describe existing biological understanding, but also to derive new understanding. For example, reaction-diiusion models which include bacterial density and nutrient concentration , can exhibit branching dynamics if the growth term is a meta-stable xed point or if the diiusion is state-dependent. We show that biologically the growth term has to be an unstable xed point, but that state-dependent diiusion can represent the lubrication uid excreted by the bacteria.