# Breaking the cell wall for efficient DNA delivery to diatoms

## TL;DR

Researchers improved DNA delivery methods for diatoms, enabling efficient genetic engineering and assembly of DNA in algal cells.

## Contribution

The study introduces optimized electroporation and PEG methods for DNA delivery and a new in vivo DNA assembly process in diatoms.

## Key findings

- Transformants can be recovered using as little as 1 ng of DNA.
- Episomes up to 55.6 kb in size can be successfully introduced into diatoms.
- DNA pieces can be assembled directly in algal cells through repair mechanisms.

## Abstract

Diatoms produce 20% of the world’s fixed organic carbon yet remain underutilized as cell factories due to limited genetic engineering tools. Here, we present optimized electroporation and polyethylene glycol (PEG) transformation methods for the model diatom Phaeodactylum tricornutum, enabling delivery of DNA and Cas9 ribonucleoprotein complexes with high efficiency. Transformants are recovered with as little as 1 ng of DNA, and linear or circular episomes as large as 55.6 kb are successfully introduced. The optimized electroporation protocol also reveals an unexpected capability: episomes can be assembled directly in the algal cell through non-homologous or homology-driven repair mechanisms, a process we term diatom in vivo assembly (DIVA). In addition, the PEG approach is adapted to successfully transform Thalassiosira pseudonana, demonstrating the applicability of our methods for engineering other diatom species. These tools could be used to accelerate diatom synthetic biology projects and, therefore, the development of sustainable technologies.

Diatoms are critical for carbon fixation and have strong biotechnology potential. Here, the authors optimized DNA and protein delivery methods for the model diatom Phaeodactylum tricornutum, also showing that DNA pieces can be stitched together directly in algal cells.