Identification and quantification of bacteria associated with cultivated Spirulina and impact of physiological factors

Master Thesis


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University of Cape Town

Research into the use of 'algal' biomass for human consumption is receiving increased attention due to their favourable nutritional value, photosynthetic efficiency, and lower requirement of land and fresh water as compared to terrestrial crops. The Spirulina species, also known as Arthrospira, is of particular interest due to its high protein content and nutritional value. Open raceway pond systems are popularly used for commercial industrial scale cultivation of microalgae due to their economic feasibility. These open cultivation systems are, however, susceptible to contamination by other microorganisms. This raises concerns relating to suitability for human ingestion and the need to control bacterial growth to prevent contamination by pathogens and to minimise the overall bacterial load. Further, bacterial contamination in processed (harvested and dried) Spirulina biomass has been reported, suggesting that some of these contaminants may end up in the market ready product where appropriate processing approaches are not used. This study sought to identify the microorganisms that typically contaminate Spirulina cultivation ponds, to understand their interaction with Spirulina biomass during cultivation and to evaluate the vulnerabilities of these contaminants, in order to generate strategies for controlling their populations during open pond cultivation. The main objectives of this study were therefore: • To quantify the bacterial load in processed Spirulina powder from a single pilot facility to ascertain the presence of the contaminant in the final product derived from the outdoor pond system used as a case study, and to quantify the bacterial load in the outdoor cultivation cultures. • To identify and characterize the bacteria associated with these Spirulina cultures and processed powder from a pilot operation carried out in Franschhoek, South Africa, with a particular focus on evaluating the likelihood for pathogens. • To establish the dynamics of the relationship between Spirulina and bacterial growth under different environmental conditions including pH, salinity and temperature. • To develop practical methods to control and minimize contamination.