The Cyanophyte Arthrospira Fusiformis in African Waters - Eco-Physiology and Potential Use in Tropical Aquaculture

Abstract: The cyanoprokaryote (blue-green algae) genus Arthrospira occurs in saline, alkaline tropical waters of Africa, Asia, and Central America. Traditionally Arthrospira has been used as a food supplement by the Kanembu tribe of Lake Chad and Aztecs living in the valley of Mexico City. It is presently cultivated in large scale throughout the world and sold as a health food supplement due to its nutritional value and potential therapeutic effects. During the past years, the genus Arthrospira has received considerable scientific and commercial attention. The purpose of the present study was to improve our understanding of the taxonomy, as well of relevant physiological and toxicological aspects of this genus by investigating Arthrospira isolated from waters from Mozambique. Further, the nutritional value of Arthrospira was also investigated, with the objective of including it as a food supplement in aquaculture. These studies were based on laboratory experiments and on in vivo bioassays. The phenotypic analysis of the isolated Arthrospira strains revealed that the two strains could be classified as A. maxima and A. fusiformis. However, molecular characterization using the sequences of the Internally Transcribed Spacer (ITS) between the 16S and 23S rRNA genes revealed that the two strains, one with a tightly coiled and the other a loosely coiled trichome and also the variant with a straight trichome (that arose from the two former strains) belonged to the ITS-cluster type I.A and were identical for the partial sequence determined. The same cluster was previously reported for Arthrospira strains isolated from other African locations. In experiments to test the adaptation of the isolated Arthrospira strains to seawater I found that the strains grow well, although at lower a rate, than in standard Zarrouk medium. I also found that proline concentration increased in cultures with high salinity, which is an indication that proline might act as an organic osmolyte whenArthrospira is exposed to high salinity. The Arthrospira strains used in the present study revealed that they produced neither microcystins nor anatoxin-a under the experimental conditions of this study. Also the mcyE gene, part of the operon encoding microcystin synthetase, was not detected, which agrees with results obtained by ELISA and HPLC. However, in the same strains I found high levels of lipopolysaccharide endotoxins (LPS). Finally, when testing Arthrospira as feed for Artemia I found that mortality of Artemia was higher on a diet of Arthrospira than on other microalgal diets, namely Isochrysis galbana and Tetraselmis suecica used as reference diets. Interestingly, although Artemia survival was lower on the Arthrospira diet, equivalent growth and faster ontogenetic development were observed for the surviving Artemia larvae as on the other microalgal diets. Possibly Arthrospira might have a positive effect on Artemia with respect to its nutritional value but some other factors such as digestion resistance and the presence of LPS might have caused the high mortality observed. These findings open an avenue for cultivation of Arthrospira in seawater in countries such as Mozambique with a long coast and great potential for aquaculture development.