Isolation and characterisation of a novel antibacterial peptide from a native swine intestinal tract-derived bacterium

- A Bacillus strain was isolated from the intestinal tract of Tibetan swine, a China-native pig.
- A novel peptide (TP) was derived from the Bacillus strain.
- TP showed great antibacterial and antitumour properties with weak haemolytic activity.
- TP inhibits Escherichia coli by penetrating cells, combining with gDNA and promoting K+ outflow.

Antimicrobial peptides (AMPs) are highly associated with antipathogenic activity, without generating drug resistance in targeted bacteria. In this study, the existence of AMPs in the Tibetan swine, a China-native, cold-resistant and seldom-sick breed of pig, was investigated. A peptide secreted by a Tibetan swine intestinal tract-derived Bacillus strain was isolated using reversed-phase chromatography (RPC), ultrafiltration and reversed-phase high-performance liquid chromatography (RP-HPLC). The peptide was identified by mass spectrometry and was characterised for activity against Escherichia coli and Staphylococcus aureus. The 16-amino acid peptide (ASVVNKLTGGVAGLLK), named TP, had a molecular mass of 1568.919 Da and exhibited inhibitory activity against Gram-positive and Gram-negative bacteria [minimum inhibitory concentrations (MICs) of 2.5-5 µM and 10-20 µM for E. coli and S. aureus, respectively] as well as human MKN-45 and NB4 tumour cell lines [50% inhibitory concentration (IC50) = 4.686 µM and 11.479 µM, respectively]. TP also exhibited weak haemolytic activity. Furthermore, TP enhanced cell membrane permeability and K+ outflow, bound with E. coli genomic DNA in vitro and inhibited E. coli growth. Thus, TP represents a strong candidate as an antibacterial peptide.