Speaker: Prof. Mitsugu Matsushita
From: Department of Physics, Chuo University, Tokyo, Japan
Date/Room/Time: Monday, November 29, 2004 /126 DeBartolo Hall/ 4-5 PM
Tea begins at 3:30 PM in Room 257 of Hurley Hall

Title: Colony Formation of Bacteria - Experiments and Modeling

Abstract:
We present experimental results of colony formation of bacteria and argue modeling attempts for them. Bacterial species Bacillus subtilis is known to exhibit at least five distinctive types of colony patterns, such as DLA, densely branched and homogeneously expanding disk ones, depending on the substrate softness and nutrient concentration. We have established the morphological diagram of colony patterns, and then examined and characterized both macroscopically and microscopically how they grow. For instance, a concentric-ring colony grows cyclically with the interface repeating an advance (migration) and a stop (consolidation) alternately. Our experimental results suggest that macroscopically the most important factor for its repetitive growth is the cell population density, i.e., that there seem to be higher threshold of the cell population density to start migrating (initiation of migration phase) and lower one to stop migrating (initiation of consolidation phase). There have been quite a few phenomenological models to explain or reproduce observed patterns of bacterial colonies. A few of them are reviewed systematically and critically, based on our experimental results.