Naturally occurring biomaterials grow bottom-up from cells into macroscale structures. Engineered living materials (ELMs) are composites of living cells incorporated into a biopolymer matrix. They are inspired by natural biomaterials but use synthetic biology to introduce tailored properties. While cells confer functionality to ELMs, the matrix defines their mechanical and physical properties. For this reason, the ability to engineer the collective self-organization of cells through a genetically encoded synthetic matrix has been a longstanding challenge in the ELM field. Previous to my work, most macroscopic ELMs either required significant processing to be assembled or were scarcely tunable. I addressed this limitation, by creating the first macroscopic de novo ELM, which grows from genetically-engineered bacteria. To achieve this goal, I engineered Caulobacter crescentus to display selfinteracting proteins by replacing the central crystallization domain of the native surface layer monomer (RsaA) with a structural domain made of elastin-like polypeptides. In this way, the hydrophobic C-termini of the RsaA become exposed and able to self-interact. I thus created a synthetic extracellular matrix that mediates cell-cell interactions. This protein was also found to be partially secreted, forming a matrix able to hierarchically organize cells over four orders of magnitude, resulting in the growth of centimeter-scale living materials. The mechanical properties of de novo ELMs can be tuned genetically over a 25-fold range by altering the structural domain of the matrix protein. I showed that these living materials can be also functionalized from complex enzyme mixtures allowing them to perform biological catalysis. Moreover, they can be employed to filter cadmium from contaminated solutions. De novo ELMs can be reshaped and used as cementing agents, they can be desiccated and reseeded to form new material. This study lays the foundation for growing ELMs with defined physical and mechanical properties, paving the way toward growing multifunctional, self-regenerating materials.

<i>De novo</i> matrix for macroscopic living materials from bacteria

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De novo matrix for macroscopic living materials from bacteria