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Development of morphological heterogeneity in glucose-limited chemostat cultures of Aspergillus oryzae

1994; Cambridge University Press; Volume: 98; Issue: 1 Linguagem: Inglês

10.1016/s0953-7562(09)80345-6

1469-8102

Julie M. Withers, Marilyn G. Wiebe, Geoffrey D. Robson, Anthony P. J. Trinci,

Microbial Metabolic Engineering and Bioproduction

Aspergillus oryzae was grown for 39 d at 34 °C in a glucose-limited chemostat culture at a dilution rate of ca 0·18 h −1 (doubling time of ca 3·85 h). During this time the parental strain was displaced and the culture became morphologically heterogeneous. Four morphological mutants were recognized: a non-sporing flat mutant, a densely sporing semi-colonial mutant, a colonial mutant and a fluffy mutant. On agar medium the flat mutant (hyphal growth unit length, G = 273 m) was more sparsely branched than the parental strain ( G = 192 m), and the densely sporing semi-colonial mutant ( G = 62 m) was more highly branched than the parental strain. The parental strain was initially displaced from the culture by the flat mutant, then by the densely sporing semi-colonial mutant, and at the end of the experiment the flat and densely sporing semi-colonial mutants made up ca 65% and ca 35% of the population respectively. Some of the morphological heterogeneity observed may have been derived from biomass which periodically accumulated on the internal surfaces of the vessel, but under the prevailing environmental conditions the densely sporing semi-colonial mutant had a selective advantage (selection coefficient = 0·04 h −1 ) over the parental strain. A second chemostat inoculated with mycelium derived from uv-irradiated conidia initially showed greater morphological heterogeneity than the one inoculated with non-irradiated conidia, but eventually this chemostat also was dominated by a non-sporing flat mutant which formed 75–80% of the population.