Competitive growth of Bacillus subtilis biofilms

Abstract

Competition for existence exists everywhere in nature. Competition includes competition between different species and competition between the same species. In this paper, Bacillus subtilis which is cultured on 1.5 wt% agar gel containing minimal salts glutamate glycerol (MSgg) medium is taken as the research object to explore the competitive behavior of the same Bacillus subtilis in the process of biofilm formation. Wide-field fluorescence microscopy is used to observe the competition of biofilms, which helps us obtain the evolvement of the edge features of the biofilm in the competition region and the distribution of different phenotypes. We find that the premature formation of the chain structure of the matrix producing cells in the competitive region restrict the outward expansion of the motile cells and thus result in the unique competition between the biofilms of Bacillus subtilis. Based on the microscopic experimental analysis of cell population collective motion during the biofilm growth, a cellular automata model of biofilm growth and evolvement is constructed. We simulate different behaviors of biofilm competition by adjusting the inoculation distance and parameters characterizing environmental pressure. The results show that the competition phenomenon of biofilm is due to the fact that matrix producing cells appear in the competition area in advance and form a barrier structure to prevent the movement and expansion of motile cells to the competition area.