Rigorous screening of a cyanobacterium for production of PHB in a closed photo-bioreactor
Significant challenges are faced concerning the selection of suitable species of microalgae for culture in photo-bioreactor systems. The selected species must meet certain criteria, depending on the culture system being considered or available. This paper presents the screening and selection of a species of cyanobacteria for production of poly-beta-hydroxybutyrate (PHB) in a closed photo-bioreactor (PBR). Six species of cyanobacteria were subjected to gross screening to determine (i) ability to produce PHB and (ii) propensity for effective culturing. The three species Anabaena solitaria, Microcystis aeruginosa and Microcystis flos-aquae survived this screening process. They were then rigorously screened under various growth conditions for maximal growth rate and PHB concentration. Each species was grown phototropically, mixotropically, and in nitrate and phosphate deficient conditions, as these were identified as the primary factors affecting PHB accumulation. All species were grown under 200 micromol/m2.s of white light, bubbled with air enriched with CO2. Growth and PHB accumulation were monitored. PHB quantification was determined using methanolasis and GC determination. Anabaena solitaria was identified as the best species for growth in the closed PBR, accumulating 4mg/L under phototropic conditions. Furthermore Anabaena solitaria performed best mixotropically and in nitrate deficient conditions.