High permeation rates in liposome systems explain rapid glyphosate biodegradation associated with strong isotope fractionation.
    
    
        
    
    
        
        Environ. Sci. Technol. 52, 7259-7268 (2018)
    
    
    
      
      
	
	    Bacterial uptake of charged organic pollutants such as the widely used herbicide glyphosate is typically attributed to active transporters, whereas passive membrane permeation as an uptake pathway is usually neglected. For 1-palmitoyl-2-oleoyl-snglycero-3-phosphocholine (POPC) liposomes, the pH-dependent apparent membrane permeation coefficients (P-app) of glyphosate, determined by nuclear magnetic resonance (NMR) spectroscopy, varied from P-app (pH 7.0) = 3.7 (+/- 0.3) x 10(-7) m.s(-1) to P-app (pH 4.1) = 4.2 (+/- 0.1) x 10(-6) m.s(-1). The magnitude of this surprisingly rapid membrane permeation depended on glyphosate speciation and was, at circumneutral pH, in the range of polar, noncharged molecules. These findings point to passive membrane permeation as a potential uptake pathway during glyphosate biodegradation. To test this hypothesis, a Gram-negative glyphosate degrader, Ochrobactrum sp. FrEM, was isolated from glyphosate-treated soil and glyphosate permeation rates inferred from the liposome model system were compared to bacterial degradation rates. Estimated maximum permeation rates were, indeed, 2 orders of magnitude higher than degradation rates of glyphosate. In addition, biodegradation of millimolar glyphosate concentrations gave rise to pronounced carbon isotope fractionation with an apparent kinetic isotope effect, AKIE(carbon), of 1.014 +/- 0.003. This value lies in the range typical of non-masked enzymatic isotope fractionation demonstrating that glyphosate biodegradation was not subject to mass transfer limitations and glyphosate exchange across the cell membrane was rapid relative to enzymatic turnover.
	
	
	    
	
       
      
	
	    
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        Publication type
        Article: Journal article
    
 
    
        Document type
        Scientific Article
    
 
    
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        Keywords
        Bioavailability Restrictions; Aerobic Biodegradation; Unilamellar Vesicles; Bacterial-membranes; Mass-spectrometry; Resistant Crops; Arthrobacter Sp; Transport; Herbicide; Soil
    
 
    
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        Publication Year
        2018
    
 
    
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        2018
    
 
    
    
        ISSN (print) / ISBN
        0013-936X
    
 
    
        e-ISSN
        1520-5851
    
 
    
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	    Volume: 52,  
	    Issue: 13,  
	    Pages: 7259-7268 
	    Article Number: ,  
	    Supplement: ,  
	
    
 
    
        
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            ACS
        
 
        
            Publishing Place
            Washington, DC
        
 
	
        
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        Reviewing status
        Peer reviewed
    
 
     
    
        POF-Topic(s)
        20403 - Sustainable Water Management
    
 
    
        Research field(s)
        Environmental Sciences
    
 
    
        PSP Element(s)
        G-504390-001
    
 
    
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        Erfassungsdatum
        2018-07-24