No abstract

Biosurfactants are a functionally and structurally heterogeneous group of biomolecules produced by multiple filamentous fungi, yeast, and bacteria, and characterized by their distinct surface and emulsifying ability. The genus Bacillus is well studied for biosurfactant production as it produces various types of lipopeptides, for example, lichenysins, bacillomycin, fengycins, and surfactins. Bacillus lipopeptides possess a broad spectrum of biological activities such as antimicrobial, antitumor, immunosuppressant, and antidiabetic, in addition to their use in skincare. Moreover, Bacillus lipopeptides are also involved in various food products to increase the antimicrobial, surfactant, and emulsification impact. From the previously published articles, it can be concluded that biosurfactants have strong potential to be used in food, healthcare, and agriculture. In this review article, we discuss the versatile functions of lipopeptide Bacillus species with particular emphasis on the biological activities and their applications in food.

Lichenysin, an amphiphilic biosurfactant with structural and physicochemical properties similar to surfactin, is produced by Bacillus licheniformis. Its low toxicity, good environmental compatibility, solubilization, foaming, emulsification and detergent activities have led to a wide range of applications in agricultural biocontrol, enhanced oil recovery, foaming agents for cosmetics and detergents for household cleaning products. However, despite the extraordinary surface-active properties and potential applications of lichenysin, the number of wild bacteria found so far is relatively low. Low titers and high costs are the main limiting factors for widespread industrial applications. In this study, a factorial design was used to optimize the composition of the medium for the production of lichenysin by Bacillus licheniformis Ali5. Firstly, the solutions of carbon, nitrogen, amino acids, inorganic salts and trace elements in the medium were evaluated in flasks using a single-factor optimization method. Meanwhile, the operating conditions were optimized in the same way. Afterwards, a partial factorial design was used to investigate the effect of six variables (five medium compositions and inoculum size) on lichenysin production. Based on the results obtained, the concentrations of sucrose and ammonium nitrate and the inoculum size were considered to be important for lichenysin production. Subsequently, a full factorial design was used to optimize these three variables. The optimized medium composition were sucrose 19.8 g/L, NH4NO3 3.9 g/L, K2HPO4·3H2O 4.0 g/L, MgSO4·7H2O 0.6 g/L, FeSO4·7H2O 0.1 g/L, CaCl2 0.01 g/L, NaCl 3.0, trace elements 1.2 mL/L. Finally, the titer of lichenysin after fed-batch fermentation reached 1425.85 mg/L, which was approximately 5.5 times higher than the titer of lichenysin from the original medium. Consequently, the method was further demonstrated to be suitable for lichenysin production.

Surfactant-like peptides are a class of small molecule short peptides with surface activity designed independently by imitating the structural characteristics of natural lipid molecules. Surfactant-like peptides have the advantages of no pollution to the environment, easy biodegradation, strong bacteriostasis, and nutrition, which accords with the development concept of the modern green industry. They are widely used in many fields such as cleaning, food, cosmetics, medicine. At present, such surfactants are mainly synthesized by expensive chemical methods. The efficient synthesis of surfactant-like peptides by biological methods has become a significant research direction. This method is environmentally friendly and can achieve low-cost and efficient production. In this study, three novel surfactant-like peptides were designed and synthesized by biological methods and successfully expressed in vitro. By optimizing of the expression host, expression vector, and fermentation conditions, the optimal expression amount was finally obtained. In addition, these surfactant-like peptides were found to have good surface activity and low critical micelle concentration. More importantly, they are pH-responsive and can self-assemble to form nanostructures in different solutions, which provides essential research value for the production of novel nanomaterials in the future. This study is the first to construct and express three novel surfactant-like peptides by biological methods, which effectively reduce the production cost compared to chemical methods; and it was also found to have excellent surfactant properties. This provides the basis for large-scale industrial production and application.