Two Engineered Bacillus subtilis Surfactin High-Producers: Effects of Culture Medium, and Potential Agricultural and Petrochemical Applications

Two genetically engineered <i>Bacillus subtilis</i> strains, BMV9 and BsB6, were evaluated in terms of culture medium (effect of nutrients on surfactin yield) and potential biotechnological applications of surfactin in agriculture and the petrochemical industry. BMV9 (<i>spo0A3</i>; <i>abrB*</i>; Δ<i>manPA</i>; <i>sfp+</i>) is, to date, the highest surfactin producer reported scientifically, and BsB6 is a <i>sfp</i>+ laboratory derivative strain that has also demonstrated considerable production potential. To assess their performance, fermentation experiments were conducted in shake flasks using two different culture media, a mineral salt medium and a complex medium, each supplemented with 2% (<i>w</i>/<i>v</i>) glucose. Lipopeptides (surfactin and fengycin) were extracted and quantified at multiple time points (up to 48 h) via high-performance thin-layer chromatography (HPTLC). Optical density, residual glucose, and pH were monitored throughout the cultivation. In parallel, microbial growth in both media were also validated in small-scale cultivation approaches. Antifungal activity of culture supernatants and lipopeptide extracts was tested against two <i>Diaporthe</i> species, key phytopathogens in soybean crops. Given the agricultural relevance of these pathogens, the biocontrol potential of lipopeptides represents a sustainable alternative to conventional chemical fungicides. Additionally, oil displacement tests were performed to evaluate the efficacy of surfactin in enhanced oil recovery (EOR), bioremediation, and related petrochemical processes. High-resolution LC-MS/MS analysis enabled structural characterization and relative quantification of the lipopeptides. Overall, these investigations provide a comprehensive comparison of strain production performance and the associated impact of cultivation media, aiming to define the optimal conditions for economically viable surfactin production and to explore its broader biotechnological applications in agriculture and the petrochemical industry.