Accelerated development of phototrophic bioprocesses : a conceptual framework

Phototrophic systems regained interest as feedstocks for bio-economy but their industrial exploitation mostly fails for economic reasons until today. Due to lacking high throughput photobioreactors and supporting methodologies, especially early stage screening suffers from low efficiency. In this context, a framework for accelerated phototrophic process development was designed. Focusing lipid production by Chlorella vulgaris as a microalgal model process, the full spectrum from strain maintenance, via cultivation and analytics to experimental design was addressed while parallelized cultivation was focused as a key technology.Contrary to well-established serial subculturing, strain maintenance was done by cryopreservation of glucose-adapted cells. Thus, an easy-to-use protocol was set up and optimized. According to specially developed growth pattern analysis, post-thawing viabilities of 63 ± 2 % were achieved and phototrophic pre-cultivation lead to highly reproducible adaptation to light.Enabling elevated throughput cultivation, a 48-well microtiter plate-based micro-photobiore-actor was designed and growth was precisely and non-invasively monitored via scattered light. Strictly controlled conditions permitted a high comparability along the wells of a plate (± 5%) while small scale and fast mixing ensured excellent light supply of the cultures. The system was shown to offer good scalability to established laboratory scale photobioreactors.To handle samples from microscale cultivation, a dye-based assay was set up and assay conditions were optimized towards efficient and precise quantification of Chlorella vulgaris’ intracellular lipid accumulation. Assay automation resulted in minimal hands-on-times while errors due to fluctuating performance of manual operators could be excluded.These technologies were merged into a framework for the accelerated development of phototrophic processes while Kriging-assisted experimental design was used to take full advantage of the improved experimental capacity. Within as little as four experimental rounds, the volumetric productivity of the model lipid production process was approximately tripled solely via medium optimization and synergistic multi-parameter interaction could be revealed.Though this framework was suitable to accelerate phototrophic process development, it may only be seen as an initial blueprint. Future improvement of the micro-photobioreactor and intensified robotic integration will enable more complex processes and thus extend the range of application from screening tasks to the acquisition of kinetic data concerning metabolism of phototrophic microorganisms or even simulation of dynamic environmental conditions