lacticin Q

Lactococcus lactis QU 5 isolated from corn produces a novel bacteriocin, termed lacticin Q. By acetone precipitation, cation-exchange chromatography, and reverse-phase high-performance liquid chromatography, lacticin Q was purified from the culture supernatant of this organism, and its molecular mass was determined to be 5,926.50 Da by mass spectrometry. Subsequent analyses of amino acid and DNA sequences revealed that lacticin Q comprised 53 amino acid residues and that its N-terminal methionine residue was formylated. In contrast to most bacteriocins produced by gram-positive bacteria, lacticin Q had no N-terminal extensions such as leader or signal sequences. It showed 66% and 48% identity to AucA, a hypothetical protein from Corynebacterium jeikeium plasmid pA501, and aureocin A53, a bacteriocin from Staphylococcus aureus A53, respectively. The characteristics of lacticin Q were determined and compared to those of nisin A. Similar to nisin A, lacticin Q exhibited antibacterial activity against various gram-positive bacteria. Lacticin Q was very stable against heat treatment and changes in pH; in particular, it was stable at alkaline pH values, while nisin A was inactivated. Moreover, lacticin Q induced ATP efflux from a Listeria sp. strain in a shorter time and at a lower concentration than nisin A, indicating that the former affected indicator cells in a different manner from that of the latter. The results described here clarified the fact that lacticin Q belongs to a new family of class II bacteriocins and that it can be employed as an alternative to or in combination with nisin A.

Lacticin Q, a lactococcal pore-forming bacteriocin, shows activity toward Gram-positive bacteria but not Gram-negative bacteria. Lacticin Q did not induce permeability of the outer membrane of Gram-negative bacteria. Experiments using model membranes containing outer membrane components suggested that lacticin Q binds to the outer membrane of Gram-negative bacteria but is unable to penetrate it. The lack of activity of lacticin Q was attributed to physicochemical features of the outer membrane components.

Lacticin Q is a 53-amino acid Class II bacteriocin produced by Lactococcus lactis QU 5. It shows antibacterial activity comparable to that of nisin A in terms of both spectrum and intensity. Moreover, it remains stable at alkaline pH values, while nisin A was inactivated. It may possibly be employed as an alternative to or in combination with nisin A. The objective of this study was to express lacticin Q extracellularly with Small ubiquitin-related modifier (SUMO) fusion technology in Bacillus subtilis. Secretory SUMO-lacticin Q fusion protein was efficiently produced in B. subtilis WB600 transformed with the recombinant expression plasmid and accounted for 19% of the culture supernatant proteins. Fusion SUMO-lacticin Q was purified by nickel nitrilotriacetate (Ni-NTA) affinity chromatography and digested with SUMO protease to release lacticin Q. Lacticin Q was further purified by Ni-NTA chromatography to yield about 2.5 mg of lacticin Q with more than 93% purity from 1L of supernatant of fermentation culture. An activity assay indicated that the recombinant bacteriocin exhibited excellent antimicrobial activity against indicator strains. The results obtained suggest that the secretory lacticin Q was efficiently expressed using SUMO fusion technology in B. subtilis. The expression and purification system could promote the application of lacticin Q in food and medicine.