Affiliation:
1. Departamento de Microbiología, Facultad de Ciencias, Universidad de Extremadura, 06071 Badajoz
2. Spanish Type Culture Collection, Universidad de Valencia, 46100, Burjassot, Valencia
3. Centro de Investigaciones Biológicas, Consejo Superior de Investigaciones Científicas, 28006 Madrid, Spain
Abstract
ABSTRACT
Cork taint is a musty or moldy off-odor in wine mainly caused by 2,4,6-trichloroanisole (2,4,6-TCA). We examined the role of 14 fungal strains isolated from cork samples in the production of 2,4,6-TCA by O methylation of 2,4,6-trichlorophenol (2,4,6-TCP). The fungal strains isolated belong to the genera
Penicillium
(four isolates);
Trichoderma
(two isolates); and
Acremonium
,
Chrysonilia
,
Cladosporium
,
Fusarium
,
Mortierella
,
Mucor
,
Paecilomyces
, and
Verticillium
(one isolate each). Eleven of these strains could produce 2,4,6-TCA when they were grown directly on cork in the presence of 2,4,6-TCP. The highest levels of bioconversion were carried out by the
Trichoderma
and
Fusarium
strains. One strain of
Trichoderma longibrachiatum
could also efficiently produce 2,4,6-TCA in liquid medium. However, no detectable levels of 2,4,6-TCA production by this strain could be detected on cork when putative precursors other than 2,4,6-TCP, including several anisoles, dichlorophenols, trichlorophenols, or other highly chlorinated compounds, were tested. Time course expression studies with liquid cultures showed that the formation of 2,4,6-TCA was not affected by a high concentration of glucose (2% or 111 mM) or by ammonium salts at concentrations up to 60 mM. In
T. longibrachiatum
the O methylation of 2,4,6-TCP was catalyzed by a mycelium-associated
S
-adenosyl-
l
-methionine (SAM)-dependent methyltransferase that was strongly induced by 2,4,6-TCP. The reaction was inhibited by
S
-adenosyl-
l
-homocysteine, an inhibitor of SAM-dependent methylation, suggesting that SAM is the natural methyl donor. These findings increase our understanding of the mechanism underlying the origin of 2,4,6-TCA on cork, which is poorly understood despite its great economic importance for the wine industry, and they could also help us improve our knowledge about the biodegradation and detoxification processes associated with chlorinated phenols.
Publisher
American Society for Microbiology
Subject
Ecology,Applied Microbiology and Biotechnology,Food Science,Biotechnology
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