Abstract: This study aimed to isolate and identify antagonistic bacteria from traditional smoked bacon, to determine the bacteriostatic activity of one selected isolate, and to purify and identify lipopeptide from its fermentation broth for the purpose of providing a theoretical basis for the application of the antimicrobial lipopeptide in food preservation. The inhibition zone method was adopted for screening the antagonistic strains. The antimicrobial lipopeptide was isolated and purified using a simple three-step procedure involving acid precipitation, silica gel column chromatography and reversed-phase high performance liquid chromatography (RP-HPLC), and it was identified by Fourier transform infrared spectroscopy (FT-IR) and matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF-MS). A total of 12 bacterial isolates were obtained, including XLP27, which had obvious antifungal and antibacterial effects on both Gram-positive and Gram-negative strains as well as one yeast strain and four mould strains. The antagonistic strain XLP27 was identified as Bacillus pumilu. The antibacterial substances produced by strain XLP27 were synthesized mainly in the stationary growth phase and the maximum yield was reached after 60 h of culture. One antimicrobial compound was purified from the fermentation broth and identified as lipopeptide iturin A, which had five isoforms with protonated masses of m/z 1 046.182, 1 060.213, 1 074.198, 1 088.201 and 1 102.175, representing fatty acid chain length of C14–C18. The lipopeptide was extremely heat stable (30 min at 40–100 ℃), remained active over a wide pH range (4–10) and was found to be resistant to all proteolytic enzymes tested. Iturin A had broad-spectrum antibacterial activity and good stability, and thus could have the potential to be an alternative to traditional antibacterial agents in the fields of food preservation and agricultural biological control.

Key words: lipopeptide; Bacillus pumilus; iturin; antifungal