Simplified Transformation of Ostreococcus tauri Using Polyethylene Glycol

Abstract

<i>Ostreococcus</i><i>tauri</i> is an easily cultured representative of unicellular algae (class Mamiellophyceae) that abound in oceans worldwide. Eight complete 13-22 Mb genomes of phylogenetically divergent species within this class are available, and their DNA sequences are nearly always present in metagenomic data produced from marine samples. Here we describe a simplified and robust transformation protocol for the smallest of these algae (<i>O. tauri</i>). Polyethylene glycol (PEG) treatment was much more efficient than the previously described electroporation protocol. Short (2 min or less) incubation times in PEG gave >10⁴ transformants per microgram DNA. The time of cell recovery after transformation could be reduced to a few hours, permitting the experiment to be done in a day rather than overnight as used in previous protocols. DNA was randomly inserted in the <i>O. tauri</i> genome. In our hands PEG was 20-40-fold more efficient than electroporation for the transformation of <i>O. tauri</i>, and this improvement will facilitate mutagenesis of all of the dispensable genes present in the tiny <i>O. tauri</i> genome.