Fig. 4.

Process of bacteria confinement in 3D hydrogel beads with desired shell thickness. Alginate polymer networks with hydrogel swelling enhance diffusion of essential substrates. Microcolony formation is noted at all depths of the core, and chemical gradients lead to unequal growth from the center to the periphery of hydrogel beads. Small substrates to support growth and viability would be preferentially consumed by the cells located at the periphery regions. The EPS components including biomass and proteins accumulate to inhibit oxygen and nutrient diffusion towards the center. The heterogenous growth leads to high local cell density contributing to considerable compression, or rupture of the hydrogel matrix. Bacteria dispersion from the beads could occur due to complex interactions with the surroundings and degradation of hydrogel-shell layer. Pattern of bacteria dispersion varies, depending on both species and environmental factors. Such lifestyle of the formed structures could be altered to tolerate exogenous stresses and adverse environments for long-term survival.