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Applied and Environmental Microbiology, March 2006, p. 2155-2162, Vol. 72, No. 3
0099-2240/06/$08.00+0 doi:10.1128/AEM.72.3.2155-2162.2006
Copyright © 2006, American Society for Microbiology. All Rights Reserved.
Institut National de la Recherche Agronomique, Unité Mixte de Recherches Génie et Microbiologie des Procédés Alimentaires, CBAI, 78850 Thiverval-Grignon, France
Received 5 October 2005/ Accepted 12 December 2005
Tracing experiments were carried out to identify volatile and nonvolatile L-methionine degradation intermediates and end products in the yeast Geotrichum candidum and in the bacterium Brevibacterium linens, both of which are present in the surface flora of certain soft cheeses and contribute to the ripening reactions. Since the acid-sensitive bacterium B. linens is known to produce larger amounts and a greater variety of volatile sulfur compounds (VSCs) than the yeast G. candidum produces, we examined whether the L-methionine degradation routes of these microorganisms differ. In both microorganisms, methanethiol and
-ketobutyrate are generated; the former compound is the precursor of other VSCs, and the latter is subsequently degraded to 2,3-pentanedione, which has not been described previously as an end product of L-methionine catabolism. However, the L-methionine degradation pathways differ in the first steps of L-methionine degradation. L-Methionine degradation is initiated by a one-step degradation process in the bacterium B. linens, whereas a two-step degradation pathway with 4-methylthio-2-oxobutyric acid (MOBA) and 4-methylthio-2-hydroxybutyric acid (MHBA) as intermediates is used in the yeast G. candidum. Since G. candidum develops earlier than B. linens during the ripening process, MOBA and MHBA generated by G.candidum could also be used as precursors for VSC production by B. linens.
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