Biosurfactants produced by Scheffersomyces stipitis cultured in sugarcane bagasse hydrolysate as new green larvicides for the control of Aedes aegypti, a vector of neglected tropical diseases

Abstract

Biosurfactants are microbial metabolites with possible applications in various industrial sectors that are considered ecofriendly molecules. In recent years, some studies identified these compounds as alternatives for the elimination of vectors of tropical diseases, such as Aedes aegypti. The major bottlenecks of biosurfactant industrial production have been the use of conventional raw materials that increase production costs as well as opportunistic or pathogenic bacteria, which restrict the application of these biomolecules. The present study shows the potential of hemicellulosic sugarcane bagasse hydrolysate as a raw material for the production of a crystalline glycolipidic BS by Scheffersomyces stipitis NRRL Y-7124, which resulted in an emulsifying index (EI24) of 70 ± 3.4% and a superficial tension of 52 ± 2.9 mN.m-1. Additionally, a possible new application of these compounds as biolarvicides, mainly against A. aegypti, was evaluated. At a concentration of 800 mg.L-1, the produced biosurfactant caused destruction to the larval exoskeletons 12 h after application and presented an letal concentration (LC50) of 660 mg.L-1. Thus, a new alternative for biosurfactant production using vegetal biomass as raw material within the concept of biorefineries was proposed, and the potential of the crystalline glycolipidic biosurfactant in larvicidal formulations against neglected tropical disease vectors was demonstrated.

Fig 1

(A) Photography of the BS produced by S. stipitis NRRL Y-7124 in the HD medium after extraction and evaporation of the solvent. (B) Optical micrograph of the crystallized BS produced by S. stipitis NRRL Y-7124 in the HD medium (magnification of 1000X).

Fig 2. TLC analysis of the BS produced by S. stipitis in the DH medium.

Fig 3. FTIR of the crystallized BS produced by S. stipitis NRRL Y-7124 in the DH medium.

(A) FTIR spectrum with wavenumbers between 402–4000 cm^-1, and (B) FTIR spectrum with wavenumbers in the fingerprint region between 402–1716 cm^-1.

Fig 4. X-ray diffractogram of the crystallized BS produced by S. stipitis NRRL Y-7124 in the DH medium.

Fig 5. HPLC chromatogram of the monosaccharides in the crystallized BS produced by S. stipitis in the DH medium.

Fig 6. Optical micrographs of A. aegypti larvae (A) without BS application (control; 400X magnification), (B) 12 h after the application of 800 mg.L^-1 of the BS produced by S. stipitis NRRL Y-7124 (400X magnification) and (C) 12 h after the application of 800 mg.L^-1 of the BS produced by S. stipitis NRRL Y-7124 (1000X magnification).