Zinc ions stimulate electrofusion of Hansenula polymorpha protoplasts

Abstract

Electrofusion of protoplasts of two mutant strains of Hansenula polymorpha resulted in high fusion and hybrid yields when the calcium ions present in the conventional fusion medium replaced by zinc ions. The optimal fusion conditions were an alignment field of 0.4 kV cm−1 strength and 2 MHz frequency for 30 s, followed by two consecutive pulses of 12 kV cm−1 strength and 15 μs duration. With 0.05–0.1 mM zinc ions in the fusion medium an average clone number of 104–105 clones per 108 input cells was reached. The presence of about 0.6 mM magnesium ions in the zinc fusion medium was essential.