Table 123

Fatty Acid Composition of S. platensis Powder

Fatty acid Fatty acids (%)

(C14) Myristic acid 0.23

(C16) Palmitic acid 46.07

(C16:1)A9 Palmitoleic acid 1.26

(C18:1)A9 Oleic acid 5.26

(C18:2)A9-12 Linoleic acid 17.43

(C18:3)A9'12'15 y-Linolenic acid 8.87

Others 20.88

Source: From Otles and Pire, 2001104.

natural pigments, and essential fatty acids, particularly y -linolenic acid, a precursor of the body's prostaglandins.89-92 It has also been reported that some cyanobacteria produce substances that can either promote or inhibit microbial growth.93-95

The fatty acid composition of Arthrospira (Spirulina) is influenced by the environmental factors and growth phase.96-98 Although the total lipid content has been shown to decrease with decrease in temperature,99 the proportion of desaturated fatty acids increases.100-102 The predominant acids of Spirulina cultures grown under standard conditions of 30°C and low irradiance (10 ^mol photon/m2/s) werepalmitic, linoleic, and y-linolenic acids (Table 12.3), which together may account for 88-92% total fatty acids.103

A decrease in temperature from 30 to 20°C, an increase in irradiance (at 30°C) from 10 to 70 ^mol photon/m2/s and transfer to dark heterotrophy all favored an increase in polyunsaturated C18 fatty acids. The highest y -linolenic acid content of any conditions was found for three strains grown heterotrophically on glucose in the dark at 30°C (Mühling et al., 2005). This is an adaptive response similar to that found in higher plants, where a temperature decrease generally leads to an increase in fatty acid desaturation of membrane lipids which is thought to compensate for the decrease in membrane fluidity at low temperatures,105 thus providing the pho-tosynthetic machinery with the ability to tolerate temperature stress (Wada et al., 1994). The desaturation to y -linolenic acid involves three different desaturation enzymes, A9, A12, and A6 desaturases that are encoded by the desC, desA, and desD genes, respectively.106 The A9 and A12 desaturases catalyze the desaturation of the first two double bonds in the fatty acids. Although it was thought that the amount of di-unsaturated fatty acids influences most the physiology of membranes at low temperatures107 it has later been shown for Arthrospira strain C1 that the expression of desC and desA was almost constant within a temperature range of 22-40°C.108 In contrast, the expression of the desD gene was strongly up-regulated upon a temperature shift from 35 to 22°C and led to an increase of y-linolenic acid.108

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