GroEL/S helps purge deleterious mutations and reduce genetic diversity during adaptive protein evolution

We study how the bacterial chaperone GroE (GroEL + GroES) affects the evolution of green fluorescent protein (GFP). To this end we subjected GFP to multiple rounds (generations) directed evolution in four replicate E. coli populations, and studied its evolutionary dynamics through high-throughput sequencing. We evolved GFP both under stabilizing selection for its ancestral (green) phenotype (phase 1), and to directional selection for a new (cyan) phenotype (phase 2). We did so both under low (G-) and high (G+) expression of GroE.