A Model for Mechanical Stress Limited Bacterial Growth and Resporulation in Confinement

In this study, we propose a self-limiting growth model for Bacillus subtilis spores confined within porous polyacrylamide (PA) hydrogels. We observed that B. subtilis spores germinate into vegetative cells within the hydrogel matrix, forming spherical colonies. These colonies expand until the mechanical stress they exert on their environment surpasses the yield stress of the hydrogel, leading to formation of a nonpermeable layer that halts nutrient diffusion and forces the bacteria to resporulate. These novel observations suggest a model to explain why bacterial growth in confined environments and material interfaces may be limited, providing insight for natural phenomena and biotechnological applications involving bacterial encapsulation.