A photobioreactor was constructed using either anchored polyurethane foam strips (1 x 1 x 40 cm, PU-strips) fixed on a stainless-steel ring to prevent flotation, or free-floating polyurethane foam blocks (1 x 1 x 1 cm, PU-blocks) as biomass supporting materials (BSM). The cyanobacterium, Scytonema sp. TISTR 8208, which produces an antibiotic, was immobilized onto PU-strips or -blocks. The free-floating PU-blocks could immobilize only about 70% of the total cells, while the anchored PU-strips could immobilize as much as 97%. PU-strips were chosen as the BSM and we named this type of reactor, seaweed-type bioreactor (STB). Optimal physical conditions for antibiotic production were determined in the STB. Inoculum density was 0.4 g l(-1) and cells were sparged with air containing 5% CO2 circulated at the gas flow rate of 250 ml min(-1) and illuminated at a light intensity of 200 mu mol photon m(-2) s(-1). The production of antibiotic could be increased 3-fold.
