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Microbiology 147 (2001), 239-246
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Microbiology (2001), 147, 239-246.
© 2001 Society for General Microbiology

Physiology and Growth

Morphological characterization of Aspergillus nidulans: growth, septation and fragmentation

Mhairi McIntyre1, Jens Dynesen1 and Jens Nielsen1

Centre for Process Biotechnology, Department of Biotechnology, Building 223, Technical University of Denmark, 2800 Lyngby, Denmark1

Author for correspondence: Jens Nielsen. Tel: +45 4525 2694. Fax: +45 4588 4148. e-mail: jn{at}ibt.dtu.dk

The influence of the sepA gene on the growth of Aspergillus nidulans has been investigated by characterizing and comparing the parental strain A28 (pabaA6 biA1) with the sepA null mutant (sepA4{Delta}Bm). The sepA gene is known to affect the septation process in A. nidulans, therefore the sepA4{Delta}Bm strain does not produce any septa during the first hours of growth. During batch cultivations sepA4{Delta}Bm shows an abrupt decrease in specific growth rate and more pronounced fragmentation (in response to elevated stirrer speed) than the parental strain. Higher specific fragmentation rates (qfrag) were obtained for the sepA4{Delta}Bm strain. The physiological reasons for the differences have been investigated by employing fluorescent stains. Computerized image analysis revealed that the more pronounced fragmentation in the mutant was due to the lower number and irregular spacing of septa (visualized by calcofluor white staining), which resulted in a weaker hyphal structure that is more vulnerable to shear stress and fragmentation than the parental strain. This led to a loss of active biomass (determined by Mag fura staining) from the hyphae of the mutant, which had failed to compartmentalize by formation of septa, in turn resulting in decreased specific growth rates for the culture.

Keywords: morphology, Aspergillus, septation, fragmentation, metabolic activity

Abbreviations: CFW, calcofluor white; DAPI, 4’,6-diamidino-2-phenylindole dihydrochloride






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Copyright © 2001 Society for General Microbiology.