Characterising the physiology of a Synechococcus strain engineered to produce squalene

Cyanobacteria are photosynthetic organisms capable of sustainable bioproduction of industrially relevant compounds, often through genetic engineering. One example is the production of squalene using engineered cyanobacteria. Squalene was traditionally harvested from shark livers and is used variously in pharmaceuticals and cosmeceuticals. This study compared the growth, transcription and production yields of a genetically modified squalene-producing cyanobacteria (Synechococcus elongatus strain BRT3-463) to its parental strain S. elongatus PCC7942. The strains were compared when grown in media with differing nitrogen and phosphate concentrations. This study observed that native regulatory networks (and in turn gene expression and cell health) were, directly or indirectly, impacted by genetic engineering. For example, ntcA, the gene encoding the global nitrogen regulator in the parental strain only had an increase in expression when grown in low nitrogen. The induced engineered strain however, downregulated ntcA under all conditions, which in turn effected the expression of NtcA-regulated phycobilisome genes nblA and cpcA. This study also revealed shortcomings of heterologous IPTG-inducible promoters which showed leaky expression and unexpectedly, variable expression in response to nutrients. The improved understanding on how native regulation is impacted by genetic engineering suggests avenues to explore for increased heterologous production yields by cyanobacteria in the future.