Nature produces materials with remarkable properties. Starting from single cells, organisms can proliferate and direct the conversion and accumulation of simple raw materials to form large structures. Following pre-programmed genetic rules, the cells that orchestrate the synthesis of these materials exert an incredible degree of control over the morphology of the structures they form. Over the course of evolution, natural biological materials have acquired a staggering range of properties – from electrical conductivity to strong underwater adhesion to thermoplasticity. Lastly, natural biological materials are not inert. The cells that produce these materials and remain associated with them are able to sense and respond to changes in their environment. However, in their natural form, the utility of these materials for applications in human industry and society is limited. Might it be possible to genetically-program living cells to create entirely new and useful biological materials? The emerging field of engineered living materials (ELMs) aims to address this question by recreating and engineering the natural processes of biological material assembly.
Here we explore two distinct strategies for the development of genetically-programmable biological ELMs. Firstly, motivated by a desire to create a modular platform for de novo ELM assembly, we developed a strategy enabling extracellular conjugation of proteins secreted by the Gram-positive bacterium, Bacillus subtilis. We demonstrate the utility of this system, not only for ELM development, but more generally for the synthetic biology and biotechnology research communities. Secondly, we developed a novel co-culture approach to produce growable bacterial cellulose (BC) materials with genetically-programmed functional properties. Specifically, inspired by the pseudo-natural microbial community of fermented kombucha tea, we recreated kombucha-like co-cultures between an engineerable BC-producing bacterium Komagataeibacter rhaeticus and the model organism and synthetic biology host Saccharomyces cerevisiae. These approaches therefore lay the groundwork for the development of an entirely new class of materials, ELMs.