title: Production of lipopeptide biosurfactants by Bacillus atrophaeus 5-2a and their potential use in microbial enhanced oil recovery.
abstract: BACKGROUND
  Lipopeptides are known as promising microbial surfactants and have been successfully used in enhancing oil recovery in extreme environmental conditions. A biosurfactant-producing strain, Bacillus atrophaeus 5-2a, was recently isolated from an oil-contaminated soil in the Ansai oilfield, Northwest China. In this study, we evaluated the crude oil removal efficiency of lipopeptide biosurfactants produced by B. atrophaeus 5-2a and their feasibility for use in microbial enhanced oil recovery.
  
  
  RESULTS
  The production of biosurfactants by B. atrophaeus 5-2a was tested in culture media containing eight carbon sources and nitrogen sources. The production of a crude biosurfactant was 0.77 g L-1and its surface tension was 26.52 ± 0.057 mN m-1in a basal medium containing brown sugar (carbon source) and urea (nitrogen source). The biosurfactants produced by the strain 5-2a demonstrated excellent oil spreading activity and created a stable emulsion with paraffin oil. The stability of the biosurfactants was assessed under a wide range of environmental conditions, including temperature (up to 120 °C), pH (2-13), and salinity (0-50 %, w/v). The biosurfactants were found to retain surface-active properties under the extreme conditions. Additionally, the biosurfactants were successful in a test to simulate microbial enhanced oil recovery, removing 90.0 and 93.9 % of crude oil adsorbed on sand and filter paper, respectively. Fourier transform infrared spectroscopy showed that the biosurfactants were a mixture of lipopeptides, which are powerful biosurfactants commonly produced by Bacillus species.
  
  
  CONCLUSIONS
  The study highlights the usefulness of optimization of carbon and nitrogen sources and their effects on the biosurfactants production and further emphasizes on the potential of lipopeptide biosurfactants produced by B. atrophaeus 5-2a for crude oil removal. The favorable properties of the lipopeptide biosurfactants make them good candidates for application in the bioremediation of oil-contaminated sites and microbial enhanced oil recovery process.
authors.affiliation: College of Natural Resources and Environment, Northwest A & F University, 3 Taicheng Road, 712100, Yangling, China.
authors.forename: Junhui
authors.initials: J
authors.lastname: Zhang
authors.affiliation: College of Natural Resources and Environment, Northwest A & F University, 3 Taicheng Road, 712100, Yangling, China. xuequanhong6070@163.com.
authors.forename: Quanhong
authors.initials: Q
authors.lastname: Xue
authors.affiliation: College of Natural Resources and Environment, Northwest A & F University, 3 Taicheng Road, 712100, Yangling, China.
authors.forename: Hui
authors.initials: H
authors.lastname: Gao
authors.affiliation: College of Natural Resources and Environment, Northwest A & F University, 3 Taicheng Road, 712100, Yangling, China.
authors.forename: Hangxian
authors.initials: H
authors.lastname: Lai
authors.affiliation: College of Earth Sciences and Resources, Chang'an University, 710055, Xi'an, China.
authors.forename: Ping
authors.initials: P
authors.lastname: Wang
mesh_terms: D001407:Bacillus / Q000737:chemistry / Q000302:isolation & purification / Q000378:metabolism*; D001673:Biodegradation, Environmental; D002681:China; D002855:Chromatography, Thin Layer; D004787:Environmental Pollution; D006863:Hydrogen-Ion Concentration; D055666:Lipopeptides / Q000096:biosynthesis* / Q000378:metabolism*; D010578:Petroleum / Q000378:metabolism*; D012988:Soil Microbiology; D017550:Spectroscopy, Fourier Transform Infrared; D013500:Surface Tension; D013501:Surface-Active Agents / Q000737:chemistry / Q000378:metabolism*; D013696:Temperature
chemical_list: D055666:Lipopeptides; D010578:Petroleum; D013501:Surface-Active Agents
keywords: Bacillus atrophaeus; Biosurfactant; Crude oil removal; Microbial enhanced oil recovery; Surface tension