Temperature-independent and -dependent expression of desaturase genes in filamentous cyanobacterium Spirulina platensis strain C1 (Arthrospira sp PCC9438)

The alteration of the degree of unsaturated fatty acids in membrane lipids has been shown to be a key mechanism in the tolerance to temperature stress of living organisms. The step that most influences the physiology of membr anes has been proposed to be the amount of di-unsaturated fatty acids in me mbrane lipids. In this study, we found that the desaturation of fatty acid to yield the di-unsaturated fatty acid 18:2(9,12), in Spirulina platensis s train C1, was not regulated by temperature. As shown by the fatty acid comp osition and gene expression patterns, the levels of 18:1(9) and 18:2(9,12) remained almost constant either when the cells were grown at 35 degrees C ( normal growth temperature) or 22 and 40 degrees C. The expression of desC ( Delta 9) and desA (Delta 12) genes, a which are responsible for the introdu ction of first and second double bonds into fatty acids, respectively, was not affected by the temperature shift from 35 to 22 degrees C or to 40 degr ees C. Only the expression and mRNA stability of the desD gene (Delta 6) th at is responsible for the introduction of a third double bond into fatty ac ids were enhanced by a temperature shift from 35 to 22 degrees C, but not t he shift from 35 to 40 degrees C. The increase in the level of desD mRNA el evated the desaturation of fatty acid from 18:2(9,12) to 18:3(6,9,12) at 22 degrees C. However, the increased level of 18.3(6,9,12) was observed after 36 h of incubation at 22 degrees C, indicating a slow response to temperat ure of fatty acid desaturation in this cyanobacterium. These findings sugge st that the desaturation of fatty acids might nor be a key mechanism in the response to the temperature change of S. platensis strain C1. (C) 2000 Fed eration of European Microbiological Societies. Published by Elsevier Scienc e B.V. All rights reserved.