High-yield production of coenzyme F420 in Escherichia coli by fluorescence-based screening of multi-dimensional gene expression space.
Coenzyme F420 is involved in bioprocesses such as biosynthesis of antibiotics by streptomycetes, prodrug activation in Mycobacterium tuberculosis, and methanogenesis in archaea. F420-dependent enzymes also attract interest as biocatalysts in organic chemistry. However, as only low F420 levels are produced in microorganisms, F420 availability is a serious bottleneck for research and application. Recent advances in our understanding of the F420 biosynthesis enabled heterologous overproduction of F420 in Escherichia coli, but the yields remained moderate. To address this issue, we rationally designed a synthetic operon for F420 biosynthesis in E. coli. However, it still led to the production of low amounts of F420 and undesired side-products. In order to strongly improve yield and purity, a screening approach was chosen to interrogate the gene expression-space of a combinatorial library based on diversified promotors and ribosome binding sites. The whole pathway was encoded by a two-operon construct. The first module (“core”) addressed parts of the riboflavin biosynthesis pathway and FO synthase for the conversion of GTP to the stable F420 intermediate FO. The enzymes of the second module (“decoration”) were chosen to turn FO into F420. The final construct included variations of T7 promoter strengths and ribosome binding site activity to vary the expression ratio for the eight genes involved in the pathway. Fluorescence-activated cell sorting was used to isolate clones of this library displaying strong F420-derived fluorescence. This approach yielded the highest titer of coenzyme F420 produced in the widely used organism E. coli so far. Production in standard LB medium offers a highly effective and simple production process that will facilitate basic research into unexplored F420-dependent bioprocesses as well as applications of F420-dependent enzymes in biocatalysis.