De Novo Engineered Living Materials from Bacteria

Engineered living materials – ELMs – are composites of living cells embedded into a biopolymer matrix. They are inspired by naturally occurring living materials, such as bones, wood, and biofilms, but use synthetic biology to introduce tailored non-natural properties to function as living sensors, therapeutics, biomanufacturing platforms, electronics, energy converters, and structural materials. While cells confer functionality to ELMs, the matrix assembles the material and defines its mechanical and physical properties, by controlling the bulk material composition, structure, and function. 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. Prior to my work, most macroscopic ELMs either required significant processing to be assembled, or were based on natural biomaterials, such as the bacterial nanocellulose, and hence minimally tunable. Here, I present the first macroscopic de novo ELM, which grows from genetically engineered bacteria. I achieved this goal by engineering Caulobacter crescentus<i> </i>to display self-interacting proteins. In this way, I created a synthetic extracellular matrix that mediates the hierarchical organization of cells over four orders of magnitude, resulting in the growth of centimeter-scale living materials. The most remarkable and unique feature of the de novo ELMs is that their mechanical properties can be controlled through genetic modifications. I showed that this living material can be functionalized from complex enzyme mixtures, allowing it to perform biological catalysis. Moreover, it retained the natural ability of single C. crescentus<i> </i>cells to bind cadmium from contaminated solutions, demonstrating the potential to be a much more useful tool for heavy metal removal than a suspension of single cells by virtue of being macroscopic, solid materials. De novo ELMs can be reshaped and used as cementing agents, forming hard hybrid materials; they can also be desiccated at room temperature and reseeded into fresh medium to form new material, facilitating their transport and storage. This study lays the foundation for growing ELMs with defined physical and mechanical properties, thus paving the way toward growing multifunctional, self-regenerating materials.