Molecular genetic manipulation of the diatom Thalassiosira pseudonana (Bacillariophyceae)

Here, we describe the first system for genetic transformation of Thalassiosira pseudonana (Hustedt) Hasle et Heimdal, the only diatom for which a complete genome sequence is presently available. This method is based on microparticle bombardment followed by selection of transformants using the antibiotic nourseothricin. It exhibits the highest transformation efficiency compared with transformation systems for other diatom species. To achieve the high transformation efficiency, it is important to allow recovery of the bombarded T. pseudonana cells in non-selective suspension culture before spreading on nourseothricin containing agar plates. It is demonstrated that T. pseudonana is readily susceptible to co-transformation allowing for the simultaneous introduction of a non-selective gene together with the selection marker gene. Both introduced genes are stably inherited even in the absence of the antibiotic selection pressure. We have developed two T. pseudonana-specific expression vectors that can drive constitutive expression (vector pTpfcp) and inducible expression (vector pTpNR) of introduced genes. In combination with the available genome data the T. pseudonana transformation system is expected to provide a powerful tool for functional genomics in diatoms.