Difference between revisions of "Part:BBa K1887002"

Revision as of 03:43, 12 October 2016

NSR

Nisin is a 34-residue antibacterial peptide and a widely used food preservative because of its potent bactericidal activity against a variety of food spoilage bacteria. However, the bactericidal efficacy of nisin has been compromised by the occurrence of nisin resistance in various bacteria. Nisin resistance in the nisin nonproducer L. lactis subsp. diacetylactis DRC3 was reported to be conferred by a specific nisin resistance gene (nsr).

Sequence and Features

Usage and Biology

Background Nisin immunity genes and nisin resistant genes Besides as the NICE system inducer, nisin is also a 34-residue antibacterial peptide produced by L. lactis that is active against a wide range of gram-positive bacteria and is therefore extensively used in the food industry as a preservative. Nisin inhibits growth of Gram-positive cells in two ways. First, it will inhibit cell wall synthesis by binding to the lipid II molecule in the membrane. Second, nisin molecules can span across the lipid bilayer, creating a pore in the cell wall which causes the cell to lysis. Because of these reasons, the L. lactis NZ9000 strain can not tolerate high levels of nisin concentration in the medium. In nisin producing strains, the nisin operon contains four nisin immunity genes, nisI, nisF, nisE and nisG. Among them, nisI encodes a lipoprotein that serves as the first defense, and is therefore always present in the cell with nisin immunity. NisF, NisE, and NisG form an ABC-exporter system, which provides the extra immunity and presents in the cell when nisin is encountered in the environment. In non-nisin-producing L. lactis, nisin resistance could be conferred by a specific nisin resistance (nsr) gene, which encodes a 35-kDa nisin resistance protein (NSR). NSR could proteolytically inactivate nisin by removing six amino acids from the carboxyl “tail” of nisin. The truncated nisin (nisin 1–28) displayed a markedly reduced affinity for the cell membrane and showed significantly diminished pore-forming potency in the membrane. A 100-fold reduction of bactericidal activity was detected for nisin 1–28 in comparison to that for the intact nisin. What’s more, the truncated nisin can still induce gene expression through the NICE system. Thus incorporation of the nisI or nsr gene into the NICE system will lead to tolerance of high levels of nisin concentration but do not have to sacrifice the gene expression capacity of the NICE system.