Protoplast fusion inAspergillus niger strains accumulating citric acid

Abstract

Auxotrophic strains of Aspergillus niger were obtained from citric-acid-producing strains of the fungus after irradiation with UV light. Protoplasts were isolated from young hyphae of the auxotrophic strains after treatment with snail enzyme and than treated with polyethylene glycol (30%, W/V), in a Ca2+ (10 mmol/L) solution. The pH value of the suspension was adjusted to 9.0. The frequency of the heterokaryons (related to the number of protoplasts reverting after PEG treatment) was 0.67%. Prototrophic heterozygous spores were isolated from a heterokaryon with the frequency of 1.2 x 10(-6). Citric acid production in the best heterozygous strains was about 15% higher than that of the high-production parent strain.

Polyploid Formation Between Aspergillus niger and Trichoderma viride For Enhanced Citric Acid Production From Cellulose

“…Protoplast fusion in filamentous fungi has proved to be a highly efficient procedure for obtaining hybrids such as heterokaryons and diploids [21,22]. Series of studies on the intraspecific protoplast fusion of A. niger, aiming to develop a new breeding system, have successfully obtained new strains with enhanced citric acid production or with some advantageous characters, different from those of the parental strains [23][24][25].…”