The release of petroleum hydrocarbons from a saline-sodic soil by the new biosurfactant-producing strain of Bacillus sp

Abstract

Adsorption of old-aged petroleum hydrocarbons to the soil solid phase, which causes biosurfactant loss of performance, is among the limiting factors for the remediation of the saline-sodic soils contaminated with petroleum. Therefore, to find a functional biosurfactant in oil-contaminated saline-sodic soils, the efficiency of 39 bacteria isolated from petroleum-contaminated soils was evaluated. The strains were cultured in the Bushnell-Haas medium, and the produced biosurfactants and bioemulsifiers in this medium were extracted using chloroform/methanol and ethyl acetate extraction methods, respectively. Their partial purification was performed by column chromatography, and eventually, their performance in releasing TPH from the contaminated soil was evaluated. The soil test results revealed that the highest TPH releases due to the effects of the biosurfactants and bioemulsifier produced from SHA302, SH21, and SH72 isolates were 42.4% ± 0.2, 21.6% ± 0.15 and 24.3% ± 0.91, respectively. Based on the 16S rRNA gene sequence, the SHA302 strain showed 93.98% phylogenetic similarity with Bacillus pumilus strain ATCC 7061. The Fourier transform infrared spectroscopy and thin-layer chromatography results proved that the biosurfactants produced by isolates SHA302, SH21 and SH72 showed lipopeptide, glycolipoprotein and glycoprotein natures, respectively. The performance of the biosurfactant produced by SHA302 isolate indicated that it could be used as a good candidate for releasing TPH from saline-sodic soils with old contamination and facilitating the degradation of hydrocarbons.

Figure 1

Evaluation of salinity stability (0–10%) in three different surfactants produced by (a) SH21, (b) SHA302 and, (c) SH72. ST surface tension, E24 emulsification test, CMD⁻¹ and CMD⁻² critical Micelle dilution of broth diluted 10 and 100 times, respectively.

Figure 2

Emulsion structure of produced biosurfactants and bioemulsifier by light optical microscope (× 40) in different concentrations of 1.2 × CMC, CMC, and 2 × CMC (in order from left to right) for isolates (a) SH21, (b) SHA302, and (c) SH72.

Figure 3

(A,B) represent the adsorption of produced biosurfactants into the contaminated soil by SH21 and SHA302, respectively, in different concentrations. (C) Adsorption of produced bioemulsifier into the contaminated soil by SH72 in different concentrations. CMC_s measured CMC in distilled water before adding it to the soil, CMC_f measured CMC after adding the surfactant to the soil (adsorption of surfactant to the soil is obtained from the difference between these two CMC).

Figure 4

The effects of different concentrations of biosurfactants and bioemulsifier on the release of TPH from the soil at two different times (1- and 7-days). (a) Surfactant produced by SH21 isolate, (b) surfactant produced by SHA302 isolate, and (c) emulsifier produced by SH72 isolate.