Production and characterization of a biosurfactant produced by Streptomyces sp. DPUA 1559 isolated from lichens of the Amazon region

Abstract

Surfactants are amphipathic compounds containing both hydrophilic and hydrophobic groups, capable to lower the surface or interfacial tension. Considering the advantages of the use of biosurfactants produced by microorganisms, the aim of this paper was to develop and characterize a biosurfactant produced by Streptomyces sp. DPUA1559 isolated from lichens of the Amazon region. The microorganism was cultured in a mineral medium containing 1% residual frying soybean oil as the carbon source. The kinetics of biosurfactant production was accompanied by reducing the surface tension of the culture medium from 60 to values around 27.14 mN/m, and by the emulsification index, which showed the efficiency of the biosurfactant as an emulsifier of hydrophobic compounds. The yield of the isolated biosurfactant was 1.74 g/L, in addition to the excellent capability of reducing the surface tension (25.34 mN/m), as observed from the central composite rotational design when the biosurfactant was produced at pH 8.5 at 28°C. The critical micelle concentration of the biosurfactant was determined as 0.01 g/mL. The biosurfactant showed thermal and pH stability regarding the surface tension reduction, and tolerance under high salt concentrations. The isolated biosurfactant showed no toxicity to the micro-crustacean Artemia salina, and to the seeds of lettuce (Lactuca sativa L.) and cabbage (Brassica oleracea L.). The biochemistry characterization of the biosurfactant showed a single protein band, an acid character and a molecular weight around 14.3 kDa, suggesting its glycoproteic nature. The results are promising for the industrial application of this new biosurfactant.

Figure 1.. Effects of pH (X₁ X12) and temperature (X₂ X22) on biosurfactant surface tension.

Figure 2.. Kinetics of growth, pH, surface tension and biosurfactant production after 120 h of fermentation.

Figure 3.. Surface tension and critical micelle concentration of the biosurfactant after 96 h of fermentation.

Figure 4.. Influence of pH on the surface tension of the biosurfactant after 96 h of fermentation.

Figure 5.. Influence of temperature on the surface tension of the biosurfactant after 96 h of fermentation.

Figure 6.. Influence of different sodium chloride concentrations on the surface tension of the biosurfactant after 96 h of fermentation.

Figure 7.. Effect of phytotoxicity of Streptomyces sp. biosurfactant on the seeds of lettuce and cabbage.