Investigation on the effects of ϵ‐poly‐L‐lysine on a producing strain Streptomyces ahygroscopicus GIM8, for better understanding its biosynthesis. (7th October 2014) - Liu, Sheng‐Rong
Abstract ϵ‐Poly‐L‐lysine (ϵ‐PL) is an L‐lysine homopolymer with strong antimicrobial activity, which is generally produced by Streptomyces strains. ϵ‐PL is only produced under acidic conditions in liquid culture, and to improve the current understanding of ϵ‐PL biosynthesis, the present study was undertaken to investigate the effects of ϵ‐PL on its producer Streptomyces ahygroscopicus GIM8, under acidic and neutral conditions. The results indicated that a neutral pH favored ϵ‐PL adsorption onto the cells, whereas minimal adsorption occurred at pH 4.0, the maximum pH for ϵ‐PL production. At pH 7.0, small amounts of ϵ‐PL caused considerable ATP leakage from the cells, which showed increased membrane permeability. Conversely, ATP leakage was inhibited by ϵ‐PL at pH 4.0. Transmission electron microscopy investigation indicated that the cytoplasmic membrane was the primary site of ϵ‐PL activity at pH 7.0, and that cell shape was maintained. Metabolic activity profiles revealed that ϵ‐PL decreased cellular metabolic activity at a relatively low rate at pH 7.0. However, the toxic effect was significantly enhanced at pH 4.0. Based on these data, a mechanism for the effect of ϵ‐PL on ϵ‐PL‐producing cells under neutral and acidic conditions is proposed. Additionally, acidic conditions may potentially be required for ϵ‐PL biosynthesis in liquid culture because low pH can increase membrane permeability and prevent binding of ϵ‐PL onto cells, both of which favor the secretion of the ϵ‐PL produced by the cells into the broth. This research contributes to the current understanding of ϵ‐PL biosynthesis.