title: Overexpression of the riboflavin biosynthetic pathway in Pichia pastoris.
abstract: BACKGROUND
  High cell density cultures of Pichia pastoris grown on methanol tend to develop yellow colored supernatants, attributed to the release of free flavins. The potential of P. pastoris for flavin overproduction is therefore given, but not pronounced when the yeast is grown on glucose. The aim of this study is to characterize the relative regulatory impact of each riboflavin synthesis gene. Deeper insight into pathway control and the potential of deregulation is established by overexpression of the single genes as well as a combined deregulation of up to all six riboflavin synthesis genes.
  
  
  RESULTS
  Overexpression of the first gene of the riboflavin biosynthetic pathway (RIB1) is already sufficient to obtain yellow colonies and the accumulation of riboflavin in the supernatant of shake flask cultures growing on glucose. Sequential deregulation of all the genes, by exchange of their native promoter with the strong and constitutive glyceraldehyde-3-phosphate dehydrogenase promoter (PGAP) increases the riboflavin accumulation significantly.
  
  
  CONCLUSIONS
  The regulation of the pathway is distributed over more than one gene. High cell density cultivations of a P. pastoris strain overexpressing all six RIB genes allow the accumulation of 175 mg/L riboflavin in the supernatant. The basis for rational engineering of riboflavin production in P. pastoris has thus been established.
authors.affiliation: Institute of Applied Microbiology, Department of Biotechnology, BOKU - University of Natural Resources and Applied Life Sciences, Muthgasse 18, 1190, Wien, Austria. diethard.mattanovich@boku.ac.at.
authors.forename: Hans
authors.initials: H
authors.lastname: Marx
authors.forename: Diethard
authors.initials: D
authors.lastname: Mattanovich
authors.forename: Michael
authors.initials: M
authors.lastname: Sauer