Fig. 1: Schematic representation of the metabolic network of growth-coupled selection strains and their role as proxy for determining rate and yields.

Black circles represent essential intermediates that act as biomass precursors. a Selection strain, where gene deletions “slice” metabolism and microbial growth becomes dependent on the supplementation of external substrates (green boxes). b Possible use of selection strains for testing different types of metabolic modules. This representation condenses all module types that can (independently) rescue growth. Each arrow color represents a particular type of module that can be screened via this approach: (i) novel assimilation route (brown); (ii) metabolic bypass for avoiding a rate-limiting step (light blue); (iii) exploration of latent promiscuous enzymatic activities (purple); and (iv) (synthetic) pathway that also produces a compound of interest (red). c Module activities will result in growth of the selection strain; monitoring biomass formation provides information related to rates and yields.