Mineral Scaffolds Enable the Morphogenesis of Bacterial Biofilms

Biofilms, or surface-attached communities of cells encapsulated in an extracellular matrix, represent a common lifestyle for many bacteria. Within a biofilm, bacterial cells often exhibit altered physiology, including enhanced resistance to antibiotics and other environmental stresses. Here we reveal a novel mechanism maintaining Bacillus subtilis and Mycobacterium smegmatis biofilms, identify the active production of calcite scaffolds. We show the distribution of minerals in the biofilm using micro-computed tomography (microCT). The microCT provides high-resolution assessments of density, geometry and microarchitecture of mineralized tissues and calcification. Furthermore, we develop a calcium carbonate quantitative method within the biofilm that teaches us about the durability and rigidity of the bacteria colony and the amount of the calcium carbonate in each location within the colony. Those scaffolds provide resistance to environmental insults, an efficient strategy for carbon dioxide sequestration also increasing overall fitness of the community. Moreover, by using Environment Scanning Electron Microscopy (ESEM) we show that extracellular matrix mutants interfere with crystal growth within biofilms. Our study sheds light on that the formation of mineral plays a cardinal and conserved role in bacterial multi-cellularity.