Nisin induction without nisin secretion
Abstract
Nisin Z, a post-translationally modified antimicrobial peptide of Lactococcus lactis, is positively autoregulated by extracellular nisin via the two-component regulatory proteins NisRK. A mutation in the nisin NisT transporter rendered L. lactis incapable of nisin secretion, and nisin accumulated inside the cells. Normally nisin is activated after secretion by the serine protease NisP in the cell wall. This study showed that when secretion of nisin was blocked, intracellular proteolytic activity could cleave the N-terminal leader peptide of nisin precursor, resulting in active nisin. The isolated cytoplasm of a non-nisin producer could also cleave the leader from the nisin precursor, showing that the cytoplasm of L. lactis cells does contain proteolytic activity capable of cleaving the leader from fully modified nisin precursor. Nisin could not be detected in the growth supernatant of the NisT mutant strain with a nisin-sensing strain (sensitivity 10 pg ml(-1)), which has a green fluorescent protein gene connected to the nisin-inducible nisA promoter and a functional nisin signal transduction circuit. Northern analysis of the NisT mutant cells revealed that even though the cells could not secrete nisin, the nisin-inducible prom...Continue Reading
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