Alteration of low-temperature susceptibility of the cyanobacterium Synechococcus sp. PCC 7002 by genetic manipulation of membrane lipid unsaturation

Cyanobacteria acclimate to low temperature by desaturating their membrane lipids. Mutant strains of Synechococcus sp. PCC 7002 containing insertionally inactivated desA (Δ12 acyl-lipid desaturase) and desB (ω3 acyl-lipid desaturase) genes were produced, and their low-temperature susceptibility was characterized. The desA mutant synthesized no linoleic acid or α-linolenic acid, and the desB mutant did not produce α-linolenic acid. The desA mutant grew more slowly than the wild-type at 22°C and could not grow at 15°C. The desB mutant could not continuously grow at 15°C, although no observable phenotype appeared at higher temperatures. It has been shown that expression of the desA gene occurs at 38°C and is up-regulated at 22°C, and that the desB gene is only expressed at 22°C. These results indicate that the expression of the desA and desB genes occurs at higher temperatures than those at which a significant decline in physiological activities is caused by the absence of their products. The temperature dependency of photosynthesis was not affected by these mutations. Since chlorosis and inability to grow at 15°C with nitrate was suppressed by the substitution of urea as a nitrogen source, it is very likely that the chilling susceptibility of the desaturase mutants is attributable to nutrient limitation.