Clocking out and letting go to unleash green biotech applications in a photosynthetic host
Cyanobacteria are attractive hosts for producing pharmaceuticals, renewable fuels, and chemicals due to their ability to use sunlight as their energy source. Despite the application of traditional genetic tools such as the identification of strong promoters to enhance the expression of heterologous genes, however, cyanobacteria have lagged behind other microorganisms such as E.coli and yeast as economically efficient bioreactors. The previous approaches have ignored large-scale constraints within cyanobacterial metabolic networks on transcription, predominantly the pervasive control of gene expression by the circadian (daily) clock. Here we adopt a novel strategy and show that reprogramming gene expression within cyanobacteria by inactivation of the circadian oscillator coupled with release of circadian repressor elements in the transcriptional regulatory pathways enables a dramatic enhancement of expression in cyanobacteria of heterologous genes encoding both catalytically active enzymes and polypeptides of biomedical significance. Overall design: To investigate the potential of the genes labA and kaiA in enhancing production of bioproducts, we created strains of the cyanobacterial model Synechococus elongatus PCC 7942 in which i) labA had been knocked-out, ii) kaiA had been overexpressed through a Zinc-induced promoter or iii) both modifications were done, and perfomed RNAseq on cultures that were given a 12h dark pulse and were collected after 12h in LL.