Identification and production of a bacteriocin from Enterococcus mundtii QU 2 isolated from soybean

Aims: Identification of the bacteriocin produced by Enterococcus mundtii QU 2 newly isolated from soybean and fermentative production of the bacteriocin. Methods and Results: The bacteriocin produced by Ent. mundtii QU 2 inhibited the growth of various indicator strains, including Enterococcus, Lactobacillus, Leuconostoc, Pediococcus and Listeria. The bacteriocin activity was stable at wide pH range and against heat treatment, but completely abolished by proteolytic enzymes. The bacteriocin was purified from the culture supernatant by the three-step chromatographic procedure. Mass spectrometry, amino acid sequencing and DNA sequencing revealed that the bacteriocin was similar to class IIa bacteriocins produced by other Ent. mundtii strains. The bacteriocin production decreased in the absence of glucose, nitrogen sources, or Tween 80 in MRS medium. Additionally, it was strongly suppressed by addition of Ca ²⁺ (CaCO₃ or CaCl₂). In pH-controlled fermentations, the highest bacteriocin production was achieved at pH 6.0 whereas the highest cell growth was obtained at pH 7.0. Conclusions: Ent. mundtii QU 2 produced a class IIa bacteriocin. Some growth factors (e.g. Ca²⁺ and pH) influenced the bacteriocin production. Significance and Impact of the Study: A new soybean isolate, Ent. mundtii QU 2 was found to be a class IIa bacteriocin producer. Factors influencing the bacteriocin production described herein are valuable for applications of the bacteriocins from Ent. mundtii strains.