Biosynthesis, characterization and potentiality of lipopeptides produced by Bacillus flexus S1 without inductive carbon sources

Abstract

This study newly isolated a bacterial stain of Bacillus flexus S1 which had abilities of synthesizing lipopeptides without any inductive operations, and thus it could effectively save operational procedures or cost. This microorganism produced 1.53 g L⁻¹ of lipopeptides with a basal medium, which was 2.59-fold higher than that with an inductive medium. Meanwhile, the sfp gene was highly expressed under non-inductive conditions. The results firstly noted micellization characteristics of a biosurfactant, including a 46.04 mg L⁻¹ critical micelle concentration, the main chemical structure, and micelles mainly distributing at 30.2–52.5 nm and 181.9–239.9 nm. The lipopeptides indicated good stability over a temperature range of 30–50 °C and pH range of 6–9. Furthermore, monatomic (K⁺ and Na⁺) and divalent (Ca²⁺ and Mg²⁺) ions respectively alleviated generating smaller and bigger micellar aggregates. The lipopeptides could effectively increase the solubility of hydrophobic organic carbons. As the lipopeptides were adopted together with oil-degrading bacteria, it increased the hydrophobicity of bacterial cells by 1.92–3.04 fold, and had low toxicity to bacterial cells. This study not only provided a new lipopeptides producing bacterium which did not need any conductive operations, but also systematically investigated the characteristics of lipopeptides, providing impactful significance for commercial application.