Validated Nuclear-Based Transgene Expression Regulated by the Fea1 Iron-Responsive Promoter in the Green Alga Chlamydomonas reinhardtii.

Microalgae are in the focus for the production of recombinant proteins in research and potential commercial application. Inducible promoters represent important tools that potentially allow the expression of recombinant proteins at higher rates. In general, they are used to separate the culture growth phase from the production phase by initiating product formation after high cell densities have been achieved. This potentially offers a higher space-time yield, consequently improving the economics of a process. In the case of the green micro alga Chlamydomonas reinhardtii, a controlled switch between activation and deactivation of gene expression is possible by changes in cultivation parameters. In this work, parameters of induction and deactivation of the iron-responsive Fea1 promoter were analyzed over time in C. reinhardtii. The results presented for the strain CC4351 validate our previous findings presented for strain CC 400. The Fea1 promoter was successfully deactivated upon transferring the cells to medium containing 10 and 20 µM Fe. Within 120 h, cells showed only 1.7-6% of the initial fluorescence. Activation of the Fea1 promoter occurred promptly and prominently when cells were transferred to iron-deplete medium. In general, both strains showed a pronounced difference between the active and the inactive states of the Fea1 promoter.