ABSTRACT

Fundamental genetic analysis of the imperfect fungus Cephalosporium acremonium was undertaken following fusion between protoplasts of nutritionally complementary strains. Protoplasts were obtained in high yields from strains of C. acremonium using the commercial enzymes Cellulase CP or Novozym 234. Other factors affecting protoplast release were investigated to maximise the effectiveness of these enzymes. Optimal conditions for the reversion and fusion of protoplasts were also established.

Haploid recombinants were isolated directly from the fusion plates after plating PEG-treated protoplasts onto a variety of selective media. To minimise any adverse effects caused by the presence of an osmotic stabilizer in the medium a method was developed using cellophane discs to transfer the developing colonies onto normal media as soon as they had become resistant to osmotic shock. Using these techniques mutations at thirteen gene loci were assigned to eight different linkage groups.

The primary colonies obtained on the fusion plates were heterogeneous consisting of haploid segregants and unstable heterozygotes (aneuploids and possible diploids). Overall the results suggest that recombination in C. acremonium occurs by a similar process to that found in other fungi with a parasexual cycle.

This work has demonstrated the value of protoplast fusion methodology in genetic investigations with this fungus. Hybridization between strains of C. acremonium and Cephalosporium chrysogenum was also achieved although these are probably identical species. However, attempts to hybridize the more distantly related species, C. acremonium and Emericellopsis minima, proved unsuccessful.

Note: Cephalosporium acremonium (now known as Acremonium chrysogenum) is used commercially to produce the ß-lactam antibiotic cephalosporin C.