High density cultivation for efficient sesquiterpenoid biosynthesis in Synechocystis sp. PCC 6803

Cyanobacteria and microalgae are attractive photoautotrophic host systems for climate-friendly production of fuels and other value-added biochemicals. However, for economic applications further development and implementation of efficient and sustainable cultivation strategies are essential. Here, we present a comparative study on cyanobacterial sesquiterpenoid biosynthesis in Synechocystis sp. PCC 6803 using a commercial lab-scale High Density Cultivation (HDC) platform in the presence of dodecane as in-situ extractant. Operating in a two-step semi-batch mode over a period of eight days, volumetric yields of (E)-alpha-bisabolene were more than two orders of magnitude higher than previously reported for cyanobacteria, with final titers of 179.4 +/- 20.7 mg * L-1. Likewise, yields of the sesquiterpene alcohols (-)-patchoulol and (-)-alpha-bisabolol were many times higher than under reference conditions, with final titers of 17.3 +/- 1.85 mg * L-1 and 96.3 +/- 2.2 mg * L-1, respectively. While specific productivity was compromised particularly for (E)-alpha-bisabolene in the HDC system during phases of high biomass accumulation rates, volumetric productivity enhancements during linear growth at high densities were more pronounced for (E)-alpha-bisabolene than for the hydroxylated terpenoids. Together, this study provides additional insights into cell density-related process characteristics, introducing HDC as highly efficient strategy for phototrophic terpenoid production in cyanobacteria.