FIG. 1.

(A) Schematic presentation of the autoregulation of nisin biosynthesis in L. lactis subsp. lactis N8 by signal transduction. Nisin is modified and secreted by the biosynthetic machinery (BCTP). Extracellular nisin activates the histidine kinase NisK, which is autophosphorylated. NisK then phosphorylates the response regulator NisR, which activates the transcription from the promoters upstream of nisZ and nisF. The nisin immunity system (IFEG) is present to protect the nisin producer, by an unknown mechanism, from being killed by nisin. (B) Schematic presentation of the nisin bioluminescence assay based on nisin signal transduction coupled to luciferase production. The sample is added to cells of LAC182, which are grown for 3 h. If the sample contains nisin, it will activate the nisF promoter upstream of the luxHb gene in plasmid pLEB535, resulting in production of luciferase. Addition of the luciferase substrate n-decyl-aldehyde (NDA) to the cells results in emission of light, which is measured by a bioluminometer.