Effect of oxygen concentration on the protein content of Spirulina biomass

Research in progress in this laboratory on the outdoor mass culture of Spirulina platensis and S. maxima haveshown that the chemical composition of Spirulina biomass changes more or less markedly according to the type of reactor in which the organism is grown. For both species, the biomass grown in closed reactors made of 14 cm-diameter polyethylene tubes (total length 400 m), in which the culture suspension is circulated with a peristaltic pump at a speed of about 3 cm/s, has a protein content lower than biomass produced in open "raceway" ponds provided with paddle wheels for the circulation of the culture suspension. It was also observed that the protein content of Spirulina grown in closed tubular reactors increased somewhat when the circulation speed of the culture was increased or when the total length of the tubular circuit was decreased. In both cases the time required by the culture to cover the entire tubular circuit was lowered. Since during the stay inside the polyethylene tubes, photosynthetically produced oxygen accumulates in considerableamounts, the observations reported above led us to investigate the influence of oxygen tension on the protein content of Spirulina biomass.