Characterization of flocculating and antimicrobial activity of salmine

Salmine is a highly cationic peptide isolated from salmon sperm. Herein, we present the first demonstration, to our knowledge, that salmine flocculates microalgae, bacteria, and fungi. The flocculating rate with Dunaliella salina reached 85.51% at 20 μg/mL. After flocculation, precipitated cells retained vitality and swimming state and could be re-cultured in fresh medium. Residual cells in the supernatant could also be re-cultured and flocculated by salmine at a rate similar to the original culture. Furthermore, salmine exhibited broad-spectrum antimicrobial activity against gram-positive and gram-negative bacteria. Two active fractions were collected by ion exchange chromatography: PEAK IV showed flocculating and antimicrobial activity, whereas PEAK III showed only weak antimicrobial activity. Amino acid analysis showed that PEAK III and PEAK IV were rich in lysine and arginine, respectively. Moreover, salmine showed good thermostability as a flocculant and antimicrobial. The flocculating properties indicate that salmine may be a potential flocculant for microalgae collection. This work provides a new method to solve the problem of microalgae collection and microalgae re-culture for agricultural and food field.