Development of Synechococcus sp. PCC 7002 as a cell factory

Cyanobacteria represent a trove of untapped potential for agricultural, medical, industrial and academic applications of primary productivity. They are a widespread group of photosynthetic prokaryotes and are known to produce a variety of polysaccharides, toxins and high-value pigments in response to environmental cues. These bacteria have been shown to monitor, adapt to, and even anticipate changes in the light and nutrient composition of the environment. There has been an increased interest for the commercial use of cyanobacteria due to their primary productivity and independence from arable land. In this study, I have contributed to the development of Synechococcus sp. PCC 7002, a fast-growing unicellular cyanobacterium with a high tolerance for salt and light, as a chassis for biotechnology via three approaches to boost high-value pigment yield: increasing growth rates/maximum cell density, enriching for specific pigments using nutrients as well as the characterization of stage-specific promoters for synthetic biology. I began by growing Synechococcus sp. PCC 7002 cultures under reduced concentrations of phosphate, nitrate, sulfate, magnesium, potassium or iron and showed previously uncharacterized changes in the maximum cell density. Finally, the activity of several candidate stage-specific heterologous promoters was tested in Synechococcus sp. PCC 7002. Several genes had previously been identified in Synechocystis PCC 6803 to have stage-specific expression based on an RNA sequencing study. The respective promoters were cloned into the pAQ1BB vector upstream of GFP and inserted into Synechococcus sp. PCC 7002 by natural transformation. In summary, the development of Synechococcus sp. PCC 7002 as a commercial organism to produce high-value compounds such as pigments was aided via a systematic investigation of growth rates and pigment composition in response to nutritional cues, as well as by characterizing the activity of heterologous candidate stage-specific promoters. This work can become foundation in the development of a tailored growth medium and novel parts for synthetic biology that may unlock the constraints to cyanobacterial productivity