In this study we exploited a modified photosynthetic electron-transfer chain (PET) in the
model cyanobacterium Synechococcus PCC 7002, where electrons derived from watersplitting
are used to power reactions catalyzed by a heterologous cytochrome P450
(CYP1A1). A simple in vivo fluorescent assay for CYP1A1 activity was employed to
determine the impact of rationally engineering of photosynthetic electron flow. This showed
that knocking out a subunit of the type I NADH dehydrogenase complex (NDH-1), suggested
to be involved in cyclic photosynthetic electron flow (∆ndhD2), can double the activity of
CYP1A1, with a concomitant increase in the flux of electrons from photosynthesis. This also
resulted in an increase in cellular ATP and the ATP/NADPH ratio, suggesting that
expression of a heterologous electron sink in photosynthetic organisms can be used to
modify the bioenergetic landscape of the cell. We therefore demonstrate that CYP1A1 is
limited by electron supply and that photosynthesis can be re-engineered to increase
heterologous P450 activity for the production of high-value bioproducts. The increase in
cellular ATP achieved could be harnessed to support metabolically demanding heterologous
processes. Furthermore, this experimental system could provide valuable insights into the
mechanisms of photosynthesis.  

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