Regulation mechanism and bioactivity characteristic of surfactin homologues with C14 and C15 fatty acid chains

Abstract

Background Surfactin, a green lipopeptide bio-surfactant, exhibits excellent surface, hemolytic, antibacterial, and emulsifying activities. However, a lack of clear understanding of the synthesis regulation mechanism of surfactin homologue components has hindered the customized production of surfactin products with different biological activities. Results In this study, exogenous valine and 2-methylbutyric acid supplementation significantly facilitated the production of C14–C15 surfactin proportions (up to 75% or more), with a positive correlation between the homologue proportion and fortified concentration. Subsequently, the branched-chain amino acid degradation pathway and the glutamate synthesis pathway are identified as critical pathways in regulating C14–C15 surfactin synthesis by transcriptome analysis. Overexpression of genes bkdAB and glnA resulted in a 1.4-fold and 1.3-fold increase in C14 surfactin, respectively. Finally, the C14-rich surfactin was observed to significantly enhance emulsification activity, achieving an EI24 exceeding 60% against hexadecane, while simultaneously reducing hemolytic activity. Conversely, the C15-rich surfactin demonstrated an increase in both hemolytic and antibacterial activities. Conclusion This study presents the first evidence of a potential connection between surfactin homologue synthesis and the conversion of glutamate and glutamine, providing a theoretical basis for targeting the synthesis regulation and structure–activity relationships of surfactin and other lipopeptide compounds. Graphical Abstract