BIOSURFACTANTS have been generating increasing interest due to their wide range of applications. This work aimed to propose a low-cost method for producing a biosurfactant using Candida tropicalis and studying its optimal conditions and applications.
A biosurfactant-producing Candida strain was selected and subjected to molecular identification. Optimum medium composition was determined using Plackett–Burman design; and response surface methodology using the central composite design. The Placket–Burman design showed that the maximum dry weight of biosurfactant (69.06mg/10mL) was obtained at the under optimal conditions of culture medium supplemented with 30g L−1 of carbon source and 1.5g L−1 of nitrogen source and incubation at 42°C for 15 days. The extracted biosurfactant was characterized using FTIR. The dye decolorization/degradation ability was tested and antibacterial/antibiofilm assays were performed using the tissue culture plate method.
Crude biosurfactant of Candida tropicalis showed good antibacterial activity, with inhibition zones ranging from 1 to 2.8cm in diameter against standard bacterial strains. Using FTIR, the biosurfactant was confirmed to be sophorolipid. High degradation rates of 50.76% and 20.88% were recorded for methylene blue and Congo red dyes, respectively, using the partially purified biosurfactant, which was further, confirmed using FTIR analysis and HPLC. The partially purified biosurfactant showed significant anti-biofilm activity against pathogenic MDR Klebsiella pneumoniae biofilm at concentrations of 100 and 50mg mL −1.
Conclusion: Candida tropicalis biosurfactant is potent at degrading different synthetic dyes in water, as well as exerting remarkable antibacterial and anti-biofilm activity against MDR pathogenic bacteria. Our results, suggest the value of using mixed substrates as low-cost substrates to increase the production of biosurfactant by Candida tropicalis.