13C-NMR study of lactate metabolism in Propionibacterium freudenreichii subsp. shermanii
Résumé
The adaptation to osmotic stress in Propionibacterium freudenreichii subsp. shermanii was investigated by using natural-abundance 13C nuclear magnetic resonance spectroscopy. Cells incubated either in a standard laboratory medium or in a medium designed to simulate the physicochemical conditions of Swiss-type cheese were found to accumulate different levels of osmotic-stress-protectant molecules. Proline, betaine, trehalose and glutamate were found simultaneously. Moreover, two types of polysaccharides were in evidence in this strain. Lactate catabolism was not mainly directed towards cell growth requirements and organic acid production but also towards biosynthesis of osmolytes requested for adaptation in a cheese environment. The possible involvement of such type of metabolite accumulation in the main cheese-ripening bacteria in Swiss-type cheeses is discussed.