Cyanobacterial secretion systems: understanding fundamental mechanisms toward technological applications

Cyanobacteria hold great promise as renewable and sustainable microbial cell factories for the production of several chemicals. In the past few years, great efforts have been employed to fine-tune metabolic pathways and fluxes toward product formation. However, focusing exclusively on the biosynthetic pathways of the target molecule, neglects two crucial aspects for the overall production capacity and process efficiency: availability of substrates and product secretion. In fact, the molecular mechanisms mediating substrate import and product export have been largely overlooked in cyanobacteria. In this context, secretion is particularly relevant, as compounds of interest may accumulate in the intracellular space, inhibiting production pathways and/or inducing toxic effects. In this chapter, we wish to raise awareness of the importance of secretion systems in cyanobacteria in the setting of biotechnological applications, highlighting what has been done in closely related bacteria, and identifying cyanobacterial candidates for improving efficient product export.