High-Throughput Screening of Cyanobacterial PHB Production Using Fluorescence-Based Detection

Three different cultures of cyanobacteria: Synechocystis sp., Leptolyngbya sp., and a co-culture of both Synechocystis sp. and Synechococcus sp. were tested for their polyhydroxybutyrate (PHB) production potential under diverse conditions. High-throughput screening in a multi-well plate, using Nile blue fluorescence to estimate PHB accumulation, enabled simultaneous testing of multiple parameters without complex setups and faster PHB estimation compared to conventional gas chromatography. Fluorescence results indicated that the best conditions for PHB accumulation were nitrogen depletion under darkness at 30°C with acetate supplementation after 4 days of glycogen accumulation. Finally, these optimal conditions were validated in single-batch proof-of-concept photobioreactors (1 L working volume). The scale-up proved successful, yielding 7% PHB dry cell weight (dcw) for Synechocystis sp. and a promising 13% PHB dcw for Leptolyngbya sp. In addition, scale-up experiments in 1-L photobioreactors demonstrated that a dedicated glycogen pre-accumulation step is unnecessary, as PHB can be efficiently synthesized directly from acetate.