Valorization of date juice by the production of lipopeptide biosurfactants by a Bacillus mojavensis BI2 strain: bioprocess optimization by response surface methodology and study of surface activities.

Lipopeptides biosurfactants (BioS) are natural surface-active compounds produced by a variety of microorganisms. They have great interest in environmental, biomedical and agro-industrial fields. However their large-scale application and production is limited by the cost of culture media and the low yield of production. Therefore, the improvement of the production yields and the development of efficient and cost-effective bioprocess became of a great interest. In this aim, we applied the response surface method to optimize an economic BioS production by a newly isolated strain Bacillus mojavensis BI2 on date Juice called "Luegmi" as unique carbon and nitrogen source. Using a Box-Bhenken design, we studied the effect of three independent variables on lipopeptide production; Leugmi concentration, Na2HPO4 and incubation time. The results of this study showed that Leugmi concentration at 25%, Na2HPO4 at 0.1% and incubation time of 24 h were optimal conditions for BioS  production, with a maximum Surface Tension (ST) decreasing capacity of 55% corresponding to 27 mN/m and an Oil Dispersing Activity (ODA) of 30 cm2 corresponding to a diameter of 6 cm. Preliminary characterization of the BioS produced on Luegmi by UV-Spectra and Thin Layer Chromatography showed its lipopeptide nature. Physic-chemical characterization of the produced lipopeptide on Leugmi showed its great surface activities and stabilities at different pH, temperature and salts concentration. The results of this study suggested that Leugmi, an agricultural byproducts can be used as a low-cost substrate to enhance the yield of lipopeptide BioS with great surface activities for potential environmental application.