Abstract
Fengycin, a lipopeptide biosurfactant, was produced by indigenous Bacillus subtilis F29-3 isolated from a potato farm. Although inhibiting the growth of filamentous fungi, the fengycin is ineffective against yeast and bacteria. In this study, fengycin was isolated from fermentation broth of B. subtilis F29-3 via acidic precipitation (pH 2.0 with 5 N HCl) followed by purification using ultrafiltration and nanofiltration. The purified fengycin product was characterized qualitatively by using fast atom bombardment-mass spectrometer, Fourier transform infrared spectrometer, ultraviolet-visible spectrophotometer, 13C-nuclear magnetic resonance spectrometer and matrix assisted laser desorption ionization-time of flight, followed by quantitative analysis using reversed-phase HPLC system. This study also attempted to increase fengycin production by B. subtilis F29-3 in order to optimize the fermentation medium constituents. The fermentation medium composition was optimized using response surface methodology (RSM) to increase fengycin production from B. subtilis F29-3. According to results of the five-level four-factor central composite design, the composition of soybean meal, NaNO3, MnSO4·4H2O, mannitol-mannitol, soybean meal-mannitol, soybean meal-soybean meal, NaNO3-NaNO3 and MnSO4·4H2O-MnSO4·4H2O significantly affected production. The simulation model produced a coefficient of determination (R2) of 0.9043, capable of accounting for 90.43% variability of the data. Results of the steepest ascent and central composite design indicated that 26.2 g/L of mannitol, 21.9 g/L of soybean meal, 3.1 g/L of NaNO3 and 0.2 g/L of MnSO4·4H2O represented the optimal medium composition, leading to the highest production of fengycin. Furthermore, the optimization strategy increased the fengycin production from 1.2 g/L to 3.5 g/L.
Highlights
As a structurally diverse group of surface-active molecules produced by microorganisms, biosurfactants have unique amphiphthic properties derived from their complex structures, including a hydrophilic moiety and a hydrophobic portion
Similar to other lipopeptides produced by B. subtilis, feygycin appears as a mixture of isoforms that vary in both the length and branching of the β-hydroxy fatty acid moiety, as well as in the amino-acid composition of the peptide ring [13]
The IR spectrum of fengycin from B. subtilis F29-3 was consistent with the literature (Figure S1(b)) [5]
Summary
As a structurally diverse group of surface-active molecules produced by microorganisms, biosurfactants have unique amphiphthic properties derived from their complex structures, including a hydrophilic moiety and a hydrophobic portion. Surfactin is a thoroughly studied and well-characterized biosurfactant [11] Such lipopeptide-type biosurfactants are characterized by their excellent surface- and membrane-active properties along with superior emulsifying and foaming properties, making them highly promising for use in food biotechnology and in the agricultural sector. Lipopeptide complex produced by B. subtilis strain F29-3, fengycin is a cyclic lipodecapeptide containing a β-hydroxy fatty acid with a side-chain length of 16–19 carbon atoms [12]. Similar to other lipopeptides produced by B. subtilis, feygycin appears as a mixture of isoforms that vary in both the length and branching of the β-hydroxy fatty acid moiety, as well as in the amino-acid composition of the peptide ring [13]. In addition to producing the lowest number of experimental runs, the response surface methodology (RSM) can help to identify the effect of individual variables on medium components, evaluate the relative significance, seek the optimum constituents, and determine the factor settings that optimize the desired response, i.e., fengycin production
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