Glycolipopeptide biosurfactant from Bacillus pumilus SG: physicochemical characterization, optimization, antibiofilm and antimicrobial activity evaluation

Abstract

The Bacillus pumilus SG isolated from soil samples at the Persian Gulf was analyzed for its ability to produce biosurfactant. Various screening techniques were used for evaluating biosurfactant production and confirming biosurfactant presence in the culture supernatant. Most n-alkanes in the bacterial culture media were effectively degraded in the presence of biosurfactant acquired from the bacteria. The highest interfacial tension (IT) reduction (42 mN/m) was obtained at 24-h fermentation time (exponential phase) and did not change significantly afterwards. The glycolipid structure of the biosurfactant was revealed through NMR and FTIR spectroscopy analysis. Two-level factorial design was then applied for optimization of biosurfactant production, where a maximal reduction of culture broth IT (30 mN/m) acquired in the presence of crude oil (0.5%, v/v), NaNO₃ (1 g/L), yeast extract (1 g/L), peptone (2 g/L) and temperature of 25 °C. The produced biosurfactant that exhibited a critical micelle concentration of 0.1 mg/ml was thermally stable. The glycolipid biosurfactant also displayed significant antibacterial activities against both Gram-positive and Gram-negative bacteria. The maximum inhibition of glycolipids biosurfactant was found against Acinetobacter strains (zone of inhibition, 45 mm). In addition, antibiofilm activities with a 50-90% biofilm reduction percent were indicated by the glycolipid biosurfactant. In conclusion, the glycolipid biosurfactant produced by B. pumilus SG revealed a wide range of functional properties and was verified as a good candidate for biomedical application. In conclusion, the glycolipid biosurfactant produced by B. pumilus SG showed a wide range of functional properties in this study, and in the case of further in vivo studies, it can be investigated a good candidate for biomedical applications such as use against biofilm or in pharmaceutical formulations.

Keywords: Antibiofilm; Antimicrobial; Bacillus pumilus SG; Glycolipopeptide biosurfactant; Optimization.

Fig. 1

a Phylogenic tree of the B. pumilus SG based on the 16S rDNA gene sequences. b Growth profile and IT alteration of B. pumilus SG

Fig. 2

The plot of actual vs. predicted surface tension by the experimental design

Fig. 3

The related 3D plots of a NaNO₃ concentration and peptone, b peptone and yeast extract concentration, c yeast extract concentration and temperature and d yeast extract and crude oil concentration versus IT as response

Fig. 4

a Gas chromatogram of negative control medium in the absence of B. pumilus SG. b the residual crude oil after cultivation of B. pumilus SG

Fig. 5

a FTIR spectrum, b ¹HNMR profile, c ¹³CNMR spectrum of glycolipid biosurfactant produced by B. pumilus SG. d Thermal gravimetric analysis (TGA, 1) and differential thermal analysis (DTA, 2) of glycolipid biosurfactant

Fig. 6

a CMC evaluation of the glycolipid biosurfactant produced by B. pumilus SG. b Antibiofilm activity of the glycolipid biosurfactant produced by B. pumilus SG