Investigation of biosurfactant production by bacterial consortium

In this study, it was aimed to produce low-cost and efficient biosurfactants using a Bacillus consortium in a medium modified with waste, to investigate the conditions affecting the production process, and to determine the properties of the produced biosurfactant. In this context, it was determined that the suitable consortium for biosurfactant production consisted of Bacillus subtilis ATCC 6633 and Bacillus halotolerans NR_115063.1 strains, based on the comparison of results obtained from drop-collapse, oil spreading, and E24 methods. Among molasses, vinasse, and curd whey waste, it was found that vinasse was the most suitable waste for biosurfactant production, with yield of 0.141 g/50 mL. At this point, it was demonstrated that using vinasse at a 10% (v/v) concentration in the medium eliminated the need for additional nitrogen sources. Consequently, by removing cost-increasing additives such as glucose and yeast extract from the medium, the biosurfactant production in the vinasse-modified BH medium increased to 0.188 g/50 mL. Aiming to further increase biosurfactant production efficiency, it was observed that when 0.75 mL of B. subtilis ATCC 6633 and 1.25 mL of B. halotolerans NR_115063.1 strains were inoculated at 4% (v/v) in the vinasse-modified BH medium containing 1‰ (v/v) trace elements, the produced biosurfactant yield increased to 0.203 g/50 mL. Additionally, the optimal physiological conditions for biosurfactant production were determined to be pH 7, 30 °C, 150 rpm, and a 10-day incubation period. Thus, the consortium, which initially produced 0.098 g/50 mL of biosurfactant, achieved a production of 0.290 g/50 mL under the conditions developed in this study. Furthermore, even with a reduced incubation period of three days under the studied physiological conditions, the production was approximately 0.2 g/50 mL, indicating minimal decline in biosurfactant yield. The biosurfactant produced in our study was identified as a lipopeptide structure using thin-layer chromatography (TLC). Additionally, nuclear magnetic resonance (NMR) and fourier-transform infrared spectroscopy (FT-IR) analyses confirmed that the produced biosurfactant had a lipopeptide structure. The biosurfactant produced in the low-cost vinasse-modified medium maintained its stability to large extent across a pH range of 4-12, NaCl concentrations varying between 5-25%, temperatures ranging from 4 to 80 °C, and UV exposure times between 10-50 minutes. This stability represents a significant advantage for the applicability of the produced biosurfactant in industries such as cosmetics, healthcare, and detergents. In conclusion, it was demonstrated that biosurfactant production in the vinasse-modified medium with the proposed consortium could be achieved at low cost and high efficiency.