EXPLORING ECONOMICAL LIPOPHILIC SUBSTRATES FOR SOPHOROLIPID SYNTHESIS BY Starmerella bombicola

MARTINI, GEORGINA; HAIDAR, CARLA NAHIR; URDAY, FABIÁN; MENZELLA, HUGO; BUSTILLO, SOLEDAD; PELLEGRINI MALPIEDI, LUCIANA

Congreso; XVIII Congreso de la Sociedad Argentina de Microbiología General; 2023

Sophorolipids (SL), a group of glycolipid-type biosurfactants, have emerged as a promising alternative to chemical and synthetic surfactants due to their high biodegradability, low toxicity, high surface activity, and various industrial applications. Microorganisms are known for producing these compounds, among which the yeast Starmerella bombicola stands out. Moreover, SLs offer an advantage as they can be produced from inexpensive residual sources or byproducts, promoting sustainable and cost-effective production process. Therefore, the aim of this work was to evaluate different lipophilic substrates in culture media to produce SL by S. bombicola. Starmerella bombicola ATCC 22214 was used as the producer microorganism in two different culture media, in which the lipid substrate varied from technical grade oleic acid to fried sunflower oil. Production culture was carried out in a final volume of 50 mL (30°C, 200 rpm). Broths were treated twice with an equal volume of ethyl acetate to estimate biomass by OD600nm and dry weight. The glucose content was determined in cell supernatants by the GOD/POD colorimetric enzymatic kit. For SL yield estimation, the ethyl acetate phase was dried until complete evaporation, and the residue obtained was washed with hexane to separate residual oil. The crude SL yield was determined by the gravimetric method. Finally, TLC and HPLC assays were performed to identify the different forms of SL present in the crude extracts. After 8 days of fermentation, cellular proliferation within the medium with oleic acid and glucose exhibited exponential growth until day 3 (OD=38). Stationary phase was observed until day 6, at which point the culture entered the death phase. The medium formed by fried sunflower oil and glucose showed diauxic cell growth with a maximum of cell growth on day 4 (OD=60). In both cases, glucose was utilized by yeast for growth at the early stationary phase and exhausted at the end of the fermentation. Regarding SL production, the highest SL yield of 13.82 g/L (day 5) was obtained with oleic acid as lipophilic substrate. Whereas with fried sunflower oil, 8.78 g/L (day 7) of SL were achieved. TLC and HPLC analyses confirmed the presence of both, acid and lactonic forms of SL in the crude extracts from both culture media tested. However, for the crude extracts of SL obtained from fried sunflower oil, a reduction of the peaks’ areas of the lactone forms of SL was observed from day 4 until their total disappearance in days 6, 7 and 8. Such behaviour is consistent with the diauxic growth curve observed, in which the sophorose from the SL is used as a carbon source for cell growth.In conclusion, although further research is needed, our results demonstrate the remarkable capacity of S. bombicola as a SL producer. This yeast can grow, produce SL, and use carbohydrate and lipid content suggesting oil byproducts could be upcycled to produce high value biosurfactants with potential industrial applications.