Analysis of biofilm expansion rate on agar substrates with different stiffness under limited nutrition

Abstract

In this study, we explore the growth of Bacillus subtilis biofilm on substrates with different agar concentrations, and obtain the area, morphology information and fluorescence intensity of biofilms by using optical imaging technologies. We find that expansion rate variations of biofilms growing on substrates with high and low agar concentration (1.5wt%, 2.0wt%,2.5wt%) are not in the same phase. In the first three days’ growth, the interaction stress between biofilm and each agar substrate increases, which makes the biofilm expansion rate decreases before wrinkle pattern IV (branches) comes up. After three days, in the later growth stage after wrinkle pattern IV appears, the biofilm has larger expansion rate growing on 2.0wt% agar concentration, which has the larger wrinkle distance in wrinkle pattern IV reducing energy consumption. The above findings are further verified through images of the fluorescence intensity of matrix producing cells of each biofilm. Our study shows that the stiff substrate does not always inhibit the biofilm expansion, although it does in the earlier stage, after that, mature biofilms acquire larger expansion rate by adjusting the growth mode through the wrinkle evolution even in nutrient extremely depletion.