Progressive transitional studies of engineered Synechococcus from laboratory to outdoor pilot-scale cultivation for production of ethylene

Cyanobacterial research is impeded by the substantial discrepancies between laboratory studies and outdoor performances, despite successful demonstrations of genetically engineered strains for array of compounds. Therefore, evaluation of adaptive responses is necessary to achieve outdoor scale-up cultivation of cyanobacteria. Under current study, cyanobacterium Synechococcus elongatus PCC7942 engineered for ethylene biosynthesis, was gradually acclimatised, ensuring sustained and progressive transition from laboratory to outdoor conditions. Bubble size of 4.9 +/- 0.2 mm and air-flow rate of 0.05 vvm in BG11 supplemented with 5 g/L bicarbonate giving mass transfer coefficient (K(L)a) of 10.48 h(-1) yielded highest specific growth rate (0.24 h(-1)) with the transformants. At the 100 L photobioreactor scale, ethylene productivity of 1.5 mL.L-1.h(-1) was achieved. A comprehensive investigation on photosynthetic responses of the transformants adapted to the outdoor conditions exhibited interesting photosynthetic electron transport regulations, involving antenna density modulation in response to diurnal and dynamic light transitions, indicating successful transition.