Expression of the Gene for the Delta 9 Acyl-Lipid Desaturase in the Thermophilic Cyanobacterium

A single-copy gene resembling the gene for the Delta 9 acyl-lipid desaturase (desC) was cloned from the thermophilic cyanobacterium Synechococcus vulcanus. Expression of desC in Escherichia coli confirmed that it encodes the Delta 9 desaturase. The nucleotide sequence of the desC was characterized by high G+C content that is typical of the sequences of thermophilic bacteria. The deduced amino acid sequence exhibited low Cys content and high Arg/Lys ratio that are the attributes of thermostable enzymes. A low level of the desC mRNA was detected in the cells grown at 55 degree C, the optimum growth temperature for S. vulcanus. About a 10-fold increase was observed in the levels of the transcript and the protein during the shift in temperature from 55 to 45 degree C. At 35 degree C the amount of the desC mRNA and of the enzyme accumulated in the cells, was 3 to 4 times smaller than at 45 degree C. At both temperatures, however, lipids were desaturated at similar rates. These results suggest that in S. vulcanus the conversion of stearic acid into oleic acid may be controlled not only by the de novo synthesis of the Delta 9 desaturase but, possibly, by the activation of the pre-existing enzyme.