Investigation on the effects of -poly-L-lysine on a producing strain Streptomyces ahygroscopicus GIM8, for better understanding its biosynthesis

• Published in: Journal of basic microbiology 2015-02, Vol.55 (2), p.172-179
• Main Authors: Liu, Sheng-Rong, Wu, Qing-Ping, Zhang, Ju-Mei, Mo, Shu-Ping, Xiao, Chun, Yang, Xiao-Juan
• Format: Article
• Language: English
• Subjects: Streptomyces
• ISSN: 0233-111X; 1521-4028
• DOI: 10.1002/jobm.201400181

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