Advertisement

Applied Microbiology and Biotechnology

, Volume 55, Issue 1, pp 85–89 | Cite as

Carrier-mediated transport of riboflavin in Ashbya gossypii

Original Paper

Abstract.

The filamentous hemiascomycete Ashbya gossypii is used for industrial riboflavin production. We examined riboflavin uptake and excretion at the plasma membrane using riboflavin auxotrophic and overproducing mutants. The riboflavin uptake system had low activity [V max=20±4 nmol min–1 g–1 mycelial dry weight (dw)] and high affinity (K M=40±12 µM). Inhibitor studies with the analogs FMN and FAD revealed high specificity of the uptake system. Excretion of riboflavin was not the consequence of non-specific permeability of the plasma membrane. Excretion rates in the mid-production phase were determined to be 2.5 nmol min–1 g–1 dw for wild-type cells and 66.7 nmol min–1 g–1 dw for an overproducing mutant, respectively. Inhibition of the reverse reaction, riboflavin uptake, led to an increase in apparent riboflavin efflux in the early production phase, indicating the presence of a separate excretion carrier. Riboflavin accumulation in A. gossypii vacuoles leading to product retention was found to be a secondary transport process. To address the question of whether a flux from the vacuoles back into the cytoplasm is present, we characterized efflux in hyphae in which the plasma membrane was permeabilized with digitonin. Efflux kinetics across the vacuolar membrane were unaffected by the lack of vacuolar H+-ATPase activity and ATP, suggesting a passive mechanism. Based on the characterization of riboflavin transport processes in this study, the design of new production strains with improved riboflavin excretion may be possible.

Keywords

ATPase Activity Riboflavin Uptake System Digitonin Vacuolar Membrane 
These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

Preview

Unable to display preview. Download preview PDF.

Unable to display preview. Download preview PDF.

Copyright information

© Springer-Verlag 2000

Authors and Affiliations

  •  
    • 1
  •  
    • 1
  •  
    • 1
  1. 1.Institut für Biochemie, Universität zu Köln, Zülpicher Strasse 47, 50674 Cologne, Germany

Personalised recommendations