Experimental Investigation on the Formation of Dense-Branching-Morphology-Like Colonies in Bacteria

We have investigated experimentally the pattern formation of bacterial colonies. We have especially examined DBM (dense-branching-morphology)-like colonies of bacterial species Bacillus subtilis . It was found from microscopic observations that many active bacterial cells collect and make a group on the tip of each growing branch. Branches repel each other and split sometimes as they grow outward. It was confirmed macroscopically that both averaged branch width < w i d t h > and averaged branch gap < g a p > decrease systematically when increasing the nutrient concentration C n , while their ratio remains unchanged with the approximate value of one. It was also found that the distribution of branch lengths is very close to exponential, suggesting that the tip-splitting of branches takes place at random.