A note on crossing experiments with Aspergillus niger for the production of calcium gluconate

A strong calcium gluconate-producing strain of Aspergillus niger (MN181) was obtained by way of mutagenic treatment. Its growth was very slow with moderate sporulation. The strain was treated with N-methyl-N'nitro-N-nitrosoguanidine (MNNG) and some auxotrophic mutants were obtained. All were less productive than the parent strain in producing calcium gluconate. The reduced yield was corrected in the heterokaryons and diploids derived by crossing sister strains. One diploid strain (D4), heterozygous for auxotrophy and conidial colour markers was grown in the presence of 4% alcohol and 31 segregants were isolated which included both haploid and diploid strains. Their yields were studied and some recombinants were obtained which, in spite of the same yield of MN181, showed improvement in giving fast growth and abundant sporulation.