We have established a high-efficiency method for transforming the unic
ellular, green alga Chlamydomonas reinhardtii by electroporation. Elec
troporation of strains CC3395 and CC425, cell wall-less mutants devoid
of argininosuccinate lyase (encoded by ARG7), in the presence of the
plasmid pJD67 (which contains ARG7) was used to optimize conditions fo
r the introduction of exogenous DNA. The conditions that were varied i
ncluded osmolarity, temperature, concentration of exogenous DNA, volta
ge and capacitance. Following optimization, the maximum transformation
frequency obtained was 2 x 10(5) transformants per mu g of DNA; this
frequency is two orders of magnitude higher than obtained with the cur
rent standard method using glass beads to introduce exogenous DNA. The
electroporation procedure described in this article is of general uti
lity, and makes it feasible to isolate genes by direct complementation
of Chlamydomonas reinhardtii mutants.