Abstract
BackgroundIonic liquids (ILs) are a promising alternative for organic solvents because these liquids exhibit unique properties and enhanced steroid 1-dehydrogenation biotransformation caused by Arthrobacter simplex CPCC 140451 (ASP). However, the effect of ILs on the whole cell itself remains poorly understood and must be further investigated.ResultsA comparative investigation was performed to determine the effect of imidazolium-based ILs, namely, hydrophobic [PrMIm]PF6, and hydrophilic [PrMIm]BF4, on the steroid conversion, activity, permeability, and material basis of ASP cells. Both ILs weakened permeability barriers, enhanced steroid transformation, whereas reduced the activity of cells. The influence of [PrMIm]PF6 on the steroid conversion, permeability and activity of cells is more serious than that of [PrMIm]BF4 Transmission electron microscopy micrographs directly showed wrinkles, gross creases, and several small pores in ILs-treated cells surface. The total lipid content of [PrMIm]BF4-treated cells reduced by 8.3 %, while that of [PrMIm]PF6-treated cells reduced twice more, among which the content of long-chain fatty acids was decreased, whereas the content of unsaturated fatty acids was increased. The protein profile of LC–MS/MS revealed that the reduced proteins of cells treated with the two ILs were mainly located in the cytoplasm and plasma membrane, 19.27 % of reduced proteins were located on the cell membrane for [PrMIm]PF6-pretreated cells, whereas only 12.8 % for [PrMIm]BF4-pretreated cells. It suggests that most reduced proteins functioned in energy production and conversion, material transport and metabolism, signal recognition and transmission, transcription, and translation and posttranslational modification. In particular, the identified differential proteins functioned in the pentose phosphate pathway, synthesis of purines and pyrimidines, and oxidative phosphorylation and fatty acid pathway.ConclusionTreatment with ILs improved permeability at the molecular level and exerted significant positive effects on steroid conversion. This study provides a material basis and elucidates the mechanisms underlying cellular changes that enhanced conversion rate.Electronic supplementary materialThe online version of this article (doi:10.1186/s12934-016-0518-3) contains supplementary material, which is available to authorized users.
Highlights
Ionic liquids (ILs) are a promising alternative for organic solvents because these liquids exhibit unique properties and enhanced steroid 1-dehydrogenation biotransformation caused by Arthrobacter simplex CPCC 140451 (ASP)
ASP cells were pretreated with two kinds of ILs and washed for three times with KH2PO4–NaOH buffer (PBS), which ensured no solubilization of ILs to the steroids
The effects among the ILs containing system, the ILs pretreated-cell system, and the control cells on steroid biotransformation were compared, and the results are shown in Fig. 1a, b
Summary
Ionic liquids (ILs) are a promising alternative for organic solvents because these liquids exhibit unique properties and enhanced steroid 1-dehydrogenation biotransformation caused by Arthrobacter simplex CPCC 140451 (ASP). Since the first report on ILs and biocatalysis involving whole-cell preparation of Rhodococcus R312 in the biphase [BMIM]PF6-water system, studies demonstrated that the high solubility of the hydrophobic compound and efficient conversion can be achieved using ILs [11]. These improvements may be due to the function of ILs as hydrophobic product reservoirs to deliver steroids into the aqueous phase while avoiding the rate-limiting step and securing effective phase separation because of the high density, low viscosity, and fine-tunable chemical properties of these liquids [12]. Paul et al suggested that [BMIM][BF4] can directly interact with the globular transport protein bovine serum albumin (BSA), which is the major component of cell membrane protein [17]
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