Enhanced bioremediation of hydraulic fracturing flowback and produced water using an indigenous biosurfactant-producing bacteria Acinetobacter sp. Y2

In this study, a biosurfactant-producing strain Y2 was isolated from hydraulic fracturing flowback and produced water (HF-FPW) and identified as Acinetobacter sp. The biosurfactant produced by Y2 could reduce surface tension of water from 72.2 mN/m to 30.2 mN/m with a CMC value of 187.5 mg/L and showed strong tolerance against wide ranges of pH (2-12), temperatures (4-100 degrees C), and salinity (0-100 g/L). Through thin layer chromatography, Fourier transform infrared spectroscopy, and gas chromatography-mass spectrometry analysis, the biosurfactant was characterized as lipopeptide. Inoculation of Acinetobacter sp. Y2 into HF-FPW greatly increased the activity and growth of the microcosm. Meanwhile, it significantly (P < 0.05) promoted the removal of chemical oxygen demand (reduction from 6646.7 mg/L to 1546.7 mg/L), and the degradation of n-alkanes (reduction from 2635.4 mg/L to 159.7 mg/L) and polycyclic aromatic hydrocarbons (reduction from 918.6 mu g/L to 209.6 mu g/L) in 7 days. High-throughput sequencing analysis revealed that the inoculation of indigenous biosurfactant producer modified the bacterial community structure and enriched the hydrocarbon-degrading microorganisms including Pseudomonas sp. and Rhizobium sp. The real-time quantitative PCR results showed that the expression of several key functional genes was greatly enhanced by Y2 addition and was significantly correlated with Acinetobacter sp. This study proved the introduction of native biosurfactant-producing microorganisms as a promising in situ strategy for HF-FPW bioremediation and the underlying mechanisms were proposed.