Characterization and partial purification of a bacteriocin produced by Leuconostoc carnosum LA44A

Abstract

Twenty Leuconostoc strains isolated from vacuum packaged Vienna-type sausages were screened for antagonistic activity against various Gram-positive organisms (including Listeria spp.). One of the three strains exhibiting inhibitory activity was chosen for further investigation. This strain was identified as Leuc. carnosum and the inhibitory substance produced was named carnosin. Carnosin was inactivated by trypsin but not by catalase or other non-proteolytic enzymes tested. Carnosin retained activity after heating at 100°C for 20 min, whereas heating at 121°C for 15 min resulted in complete loss of activity. Carnosin was active at pH values ranging from 2 to 9. Carnosin activity was not detectable until cells were in the late log-phase of growth. At low temperatures (4°C), higher cell densities were required before carnosin activity could be detected. Carnosin was active against various lactic acid bacteria, Enterococcus faecalis and Enterococcus faecium and against Listeria spp. Difficulties in purification were reduced by growing Leuc. carnosum in a modified MRS medium, having 50% of the normal peptone concentration and no Tween or meat extract. Sodium dodecyl sulphate polyacrylamide gel electrophoresis of partially purified carnosin indicated that it has a molecular mass between 2510 and 6000 Da. Yet, retention of activity after exhaustive dialysis suggested a molecular mass > 14kDa. It is hypothesized that carnosin forms large active complexes which can be dissociated to small (active) components.