Desaturase genes in a psychrotolerant Nostoc sp. are constitutively expressed at low temperature

Antarctic psychrotolerant, Nostoc sp. (SO-36), when grown at 25 °C and then shifted to 10 °C, showed an increase in the tri-unsaturated fatty acid [C18:3(9,12,15)] at the expense of mono- [C18:1(9)] and di-unsaturated [C18:2(9,12)] fatty acids. These results indicate that the activities of the enzymes DesA and DesB are up-regulated, when cultures were grown at 10 °C or shifted to 10 °C from 25 °C. However, RT-PCR studies indicated a constitutive expression of desA, desB, desC, and desC2 genes when cultures grown at 25 °C were shifted to 10 °C. This constitutive expression of des genes is in contrast to that observed in mesophilic cyanobacteria, in which desA and desB are transcriptionally up-regulated in response to lowering of growth temperature.