Detection and preliminary characterization of a narrow spectrum bacteriocin produced by lactobacillus pentosus K2N7 from Thai traditional fermented shrimp (Kung-Som)

A total of 48 lactic acid bacteria (LAB) exhibited antagonistic activity against Lactobacillus sakei subsp. sakei JCM 1157 or Staphylococcus aureus DMST 8840. Only strain K2N7 was selected for characterization of bacteriocin activity. It was identified as Lactobacillus pentosus based on 16S rDNA analysis. The maximum bacteriocin production was detected in early stationary phase of growth. It was found to be sensitive to proteolytic enzymes (trypsin, proteinase K, pronase E and α-chymotrypsin). The bacteriocin K2N7 was heat stable (2 h at 100ºC) and retained activity over a wide pH range (2.0-12.0). Bacteriocin K2N7 has a narrow inhibitory spectrum restricted to genus Lactobacillus including Lactobacillus plantarum D6SM3, a bacterial strain known to cause overfermentation in Kung-Som. The peptide was purified by 60% ammonium sulphate precipitation followed by sequential cation exchange chromatography and hydrophobic interaction characteristic. The molecular mass of bacteriocin K2N7 (2.017 kDa) was determined by matrix-assisted laser desorption/ionization time-offlight mass spectrometry analysis (MALDI-TOF MS).