Involvement of an N-acetylglucosaminidase in autolysis of Propionibacterium freudenreichii CNRZ 725

• Published in: Applied and Environmental Microbiology Vol. 60; no. 12; pp. 4351 - 4358
• Main Authors: LEMEE, R, LORTAL, S, CESSELIN, B, VAN HEIJENOORT, J
• Format: Journal Article
• Language: English
• Published: Washington, DC American Society for Microbiology 01.12.1994
• Subjects: actividad enzimatica; activite enzymatique; Bacteria; Bacteriology; Biological and medical sciences; Cellular biology; Cheese; cultivos iniciadores; culture starter; Ecology, environment; enzymic activity; Food industries; Food Microbiology; Fundamental and applied biological sciences. Psychology; Life Sciences; Milk and cheese industries. Ice creams; Propionibacterium freudenreichii; starter cultures; Cheese ripening; Temperature; Enzyme; Environmental factor; Propionibacterium freudenreichii; Cell wall; Autolysis; α-N-Acetylglucosaminidase; Glycosidases; Morphology; Propionibacteriaceae; Microorganism culture; pH; Bacteria; Hydrolases; Actinomycetes; O-Glycosidases; Swiss cheese
• ISSN: 0099-2240; 1098-5336
• DOI: 10.1128/aem.60.12.4351-4358.1994

Propionibacterium freudenreichii plays an important role in Swiss cheese ripening (it produces propionic acid, acetic acid, and CO2). Moreover, autolysis of this organism certainly contributes to proteolysis and lipolysis of the curd because intracellular enzymes are released. By varying external factors, we determined the following conditions which promoted autolysis of both whole cells and isolated cell walls of P. freudenreichii CNRZ 725: (i) 0.1 M potassium phosphate buffer (pH 5.8) at 40 degrees C and (ii) 0.05 to 0.1 M KCl at 40 degrees C. We found that early-exponential-phase cells possessed the highest autolytic activity. It should be emphasized that the pH of Swiss cheese curd (pH 5.5 to 5.7) is near the optimal pH which we determined. Ultrastructural observations by electron microscopy revealed a 16-nm-thick homogeneous cell wall, as well as degradation of the cell wall that occurred concomitantly with cell autolysis. In the presence of 0.05 M potassium chloride, there was a great deal of isolated cell wall autolysis (the optical density at 650 nm decreased 77.5% +/- 7.3% in 3 h), and one-half of the peptidoglycan material was released. Finally, the main autolytic activity was due to an N-acetylglucosaminidase activity.