In every biotechnological production process, the ultimately crucial question is how much of the invested nutrient resources such as carbon, nitrogen, sulfur, or phosphate sources goes into the product and how much goes into production of cell mass. Even though in selected cases other considerations might be similarly important (such as product formation per time), this fundamental question determines whether a process will be successful or not. In this proposal, we suggest a completely novel approach of identifying genes and networks of central importance for allocating increasing fractions of a substrate flux to an industrial model product, vitamin B2 (riboflavin). Specifically, we propose to systematically vary, one by one and in combination, the translation levels of proteins belonging to the core metabolism of Escherichia coli as a model production organism and subsequently to evaluate the (millions of) resulting different strains for channeling steadily increasing substrate fluxes to product formation instead of growth. Due to the application of a novel nanoliter reactor technology, the evaluation of variant strains can be performed in ultra-high throughput mode (several millions per week) under substrate-limiting conditions, which is the most accurate reflection of the physiological challenges of producer cells in industrially relevant settings. This ability to screen large numbers of variant strains under substrate limiting conditions is fundamentally different from most other screening procedures and certainly unique at this level of throughput.
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