Sequential Polydopamine/Polyethylenimine Deposition Converts <i>Escherichia coli</i> into Gravity-Sedimenting Engineered Living Materials for Biocatalysis

Microbial whole-cell biocatalysis is frequently bottlenecked by physical handling and downstream separation rather than by intrinsic biochemistry. Conventional immobilization strategies struggle to reconcile these challenges: bulk matrices incur severe mass-transfer limitations, while single-cell nanocoatings preserve diffusion but fail to confer macroscopic handling properties. Here, we report a bottom-up engineered living material strategy that converts planktonic cells into macroscopic, gravity-sedimenting granules via the sequential deposition of polydopamine (PDA) and branched polyethylenimine (bPEI). This cross-linking process requires polymer loadings of approximately 0.2 wt %, relying on the cells themselves to serve as the structural scaffold. The resulting conformal coating imposes a physical constraint that induces targeted growth arrest, an engineered outcome that eliminates substrate competition for biomass proliferation whilepreserving the metabolic, transcriptional, and hydrolytic activities. We demonstrate that these granular ELMs are easily separated by gravity, allowing for direct reuse across multiple batch cycles and enabling operation as a self-retaining catalytic bed in continuous-flow reactors without external support matrices. Furthermore, we establish the generality of this platform by applying an identical coating protocol to Escherichia coli, industrially relevant yeasts, and the cyanobacterium Synechocystis. This minimal-coating system bridges the gap between single-cell catalytic efficiency and bulk material handleability for intensified bioprocessing.