We then proceeded to compare the monomer conversion, as well as the number-average molecular weight (Mn) and dispersity (Đ) of PPEGMA in different conditions. To this end, PPEGMA was detached from the proteins after PEGMA polymerization and characterized by gel permeation chromatography (Mn and Đ) and NMR spectroscopy (monomer conversion) (Table , SI Figure ). In the absence of surface-displayed HRP and initiator/CTA, monomer conversion was low (P1). When comparing ATRP and RAFT free in solution (1-step process, conjugation contemporary to polymerization) versus tethered to the surface (2-steps, polymerization after conjugation) (P2 and P3 vs P4 and P5, SI Figure ), the 2-step conjugation proved to achieve better conversion and lower dispersity. Cells performing ATRP also consistently showed a better viability (generally >70%) than cells subjected to RAFT polymerization (<50% viability) (SI Figure ). A control experiment with the initiator but without expressed HRP showed low -but non-negligible-monomer conversion (23%), suggesting residual activity on the surface of yeast (P6). To probe for polymerization between cells, HRP-displaying yeast were combined with yeast cells lacking HRP but possessing the ATRP initiator (SI Figure ). The monomer conversion remained low, showing that no inter-cell polymerization occurred (P7). Thus, the polymerization on the cell surface requires both the enzyme and the initiator on the same cell.