Novel antimicrobial activities of a peptide derived from a Japanese soybean fermented food, Natto, against Streptococcus pneumoniae and Bacillus subtilis group strains

We recently isolated a tumoricidal peptide from Natto, a Japanese traditional fermented food. In the present study, antimicrobial activity of the Natto peptide was examined. The peptide consisted of 45 amino acid residues, and its structure was predicted to be rich in α-helix. It excreted antimicrobial activity only against Streptococcus pneumoniae and Bacillus subtilis group (B. subtilis, Bacillus pumilus, and Bacillus licheniformis). Lesser antimicrobial activity was observed for Streptococcus species other than S. pneumoniae. Hemolysate or hemin was required for the antimicrobial activity of the peptide. The Natto peptide damages the cell membrane of B. subtilis. On the other hand, chain morphology was induced in S. pneumoniae, which is naturally diplococcus, during the early phases of the Natto peptide treatment; following that the cells were rapidly lysed. This suggested that the Natto peptide displayed a novel narrow spectrum of bactericidal activity and inhibited cell separation during cell division of S. pneumoniae.