C-13-NMR STUDY OF LACTATE METABOLISM IN PROPIONIBACTERIUM-FREUDENREICHII SUBSP SHERMANII

The adaptation to osmotic stress in Propionibacterium freudenreichii s ubsp. shermanii was investigated by using natural-abundance C-13 nucle ar magnetic resonance spectroscopy. Cells incubated either in a standa rd laboratory medium or in a medium designed to simulate the physicoch emical conditions of Swiss-type cheese were found to accumulate differ ent levels of osmotic-stress-protectant molecules. Proline, betaine, t rehalose 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 f or adaptation in a cheese environment. The possible involvement of suc h a type of metabolite accumulation in the main cheese-ripening bacter ia in Swiss-type cheeses is discussed.