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Impairment of cobalt-induced riboflavin biosynthesis in a Debaryomyces hansenii mutant

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Flavinogenic yeasts such as Debaryomyces hansenii overproduce riboflavin (RF) in the presence of heavy metals. Growth and RF production were compared between wild-type D.hansenii and a RF production-impaired metal-tolerant ura3 mutant in the presence of sublethal cobalt(II) concentrations. Debaryomyces hansenii (wild type) exhibits an extended lag phase with an increase in RF synthesis. Supplementation of exogenous uracil shortened the lag phase at the highest concentration of cobalt(II) used, suggesting that uracil has a possible role in metal acclimation. The D.hansenii ura3 mutant isolated by chemical mutagenesis exhibited a higher level of metal tolerance, no extended lag phase, and no marked increase in RF synthesis. Transformation of the mutant with the URA3 gene isolated from Saccharyomyces cerevisiae or D.hansenii did not restore wild-type characteristics, suggesting a second mutation that impairs RF oversynthesis. Our results demonstrate that growth, metal sensitivity, and RF biosynthesis are linked.

Les levures flavinogènes comme Debaryomyces hansenii produisent un surplus de riboflavine (RF) en présence de métaux lourds. La croissance et la production de RF de la souche D.hansenii sauvage ont été comparées à celle d’une souche mutante ura3, déficiente en production de RF et tolérante aux métaux en présence de concentrations sub-létales de cobalt(II). Debaryomyces hansenii sauvage présente une phase de latence prolongée et une augmentation de la synthèse de RF. La supplémentation en uracile exogène a diminué la phase de latence en présence de la plus forte concentration de cobalt(II) utilisée, ce qui suggère que l’uracile puisse jouer un rôle dans l’acclimatation aux métaux. Le mutant ura3 de D.hansenii isolé par mutagenèse chimique présentait un niveau plus élevé de tolérance aux métaux, sans phase de latence prolongée et sans synthèse marquée de RF. La transformation du mutant avec le gène URA3 isolé de Saccharomyces cerevisiae ou de D.hansenii n’a pas restauré les caractéristiques sauvages, ce qui suggère qu’une seconde mutation empêche le synthèse d’un surplus de RF. Nos résultats démontrent que la croissance, la sensibilité aux métaux et la biosynthèse de RF sont liées.

Document Type: Research Article

Publication date: 2007-11-01

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  • Published since 1954, this monthly journal contains new research in the field of microbiology including applied microbiology and biotechnology; microbial structure and function; fungi and other eucaryotic protists; infection and immunity; microbial ecology; physiology, metabolism and enzymology; and virology, genetics, and molecular biology. It also publishes review articles and notes on an occasional basis, contributed by recognized scientists worldwide.
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