Variation in fatty acid composition of Arthrospira (Spirulina) strains

Abstract

A study of the fatty acid composition was made for 35 Arthrospira strains, concentrating on the most abundant fatty acids, the two polyunsaturated C18 acids, linoleic and γ -linolenic acid, and palmitic acid. When grown at 30 ◦ C and low irradiance (10 µmol photon m −2 s −1 ), these three acids together formed 88‐92% of total fatty acids. There were considerable differences in the composition of the two polyunsaturated acids. Depending on the strain, linoleic acid formed 13.1‐31.5% and γ -linolenic acid formed 12.9‐29.4% total fatty acids. In contrast, the range for palmitic acid was narrow: 42.3‐47.6% of total fatty acids. Repeat experiments on several strains under defined conditions led to closely similar results for any particular environment, suggesting that fatty acid composition can be used as an aid in differentiating between strains. Five additional strains, which had apparently originated from the same original stock cultures as 3 of the 35 in the main study, but from different culture collections, were also assayed. With four strains the results were similar, irrespective of culture source, but with one strain marked differences occurred, especially in the polyunsaturated C18 fatty acid fraction. These differences were independent of the age of the culture. In addition, straight morphotypes derived during repeat subcultures of four strains; each showed a similar fatty acid composition to that of the helical morphotypes of the same strains. A decrease in temperature from 30 to 20 ◦ C, an increase in irradiance (at 30 ◦ C) from 10 to 70 µmol photon m −2 s −1 and transfer to dark heterotrophy all favoured an increase in polyunsaturated C18 fatty acids. The highest γ -linolenic acid content of any conditions was found for three strains grown heterotrophically on glucose in the dark at 30 ◦ C. A comparative study of six strains of Spirulina confirmed a previous study showing the absence of γ -linolenic acid in all Spirulina strains, thus permitting the separation of these two genera.