TY - JOUR
T1 - Analysis of composition and structure of Clostridium thermocellum membranes from wild-type and ethanol-adapted strains
AU - Timmons, Michael D.
AU - Knutson, Barbara L.
AU - Nokes, Sue E.
AU - Strobel, Herbert J.
AU - Lynn, Bert C.
PY - 2009/4
Y1 - 2009/4
N2 - Clostridium thermocellum is a candidate organism for consolidated bioprocessing of lignocellulosic biomass into ethanol. However, commercial use is limited due to growth inhibition at modest ethanol concentrations. Recently, an ethanol-adapted strain of C. thermocellum was produced. Since ethanol adaptation in microorganisms has been linked to modification of membrane lipids, we tested the hypothesis that ethanol adaptation in C. thermocellum involves lipid modification by comparing the fatty acid composition and membrane anisotropy of wild-type and ethanol-adapted strains. Derivatization to fatty acid methyl esters provided quantitative lipid analysis. Compared to wild-type, the ethanol-adapted strain had a larger percentage of fatty acids with chain lengths >16:0 and showed a significant increase in the percentage of 16:0 plasmalogens. Structural identification of fatty acids was confirmed through mass spectral fragmentation patterns of picolinyl esters. Ethanol adaptation did not involve modification at sites of methyl branching or the unsaturation index. Comparison of steady-state fluorescence anisotropy experiments, in the absence and presence of ethanol, provided evidence for the effects of ethanol on membrane fluidity. In the presence of ethanol, both strains displayed increased fluidity by approximately 12%. These data support the model that ethanol adaptation was the result of fatty acid changes that increased membrane rigidity that counter-acted the fluidizing effect of ethanol.
AB - Clostridium thermocellum is a candidate organism for consolidated bioprocessing of lignocellulosic biomass into ethanol. However, commercial use is limited due to growth inhibition at modest ethanol concentrations. Recently, an ethanol-adapted strain of C. thermocellum was produced. Since ethanol adaptation in microorganisms has been linked to modification of membrane lipids, we tested the hypothesis that ethanol adaptation in C. thermocellum involves lipid modification by comparing the fatty acid composition and membrane anisotropy of wild-type and ethanol-adapted strains. Derivatization to fatty acid methyl esters provided quantitative lipid analysis. Compared to wild-type, the ethanol-adapted strain had a larger percentage of fatty acids with chain lengths >16:0 and showed a significant increase in the percentage of 16:0 plasmalogens. Structural identification of fatty acids was confirmed through mass spectral fragmentation patterns of picolinyl esters. Ethanol adaptation did not involve modification at sites of methyl branching or the unsaturation index. Comparison of steady-state fluorescence anisotropy experiments, in the absence and presence of ethanol, provided evidence for the effects of ethanol on membrane fluidity. In the presence of ethanol, both strains displayed increased fluidity by approximately 12%. These data support the model that ethanol adaptation was the result of fatty acid changes that increased membrane rigidity that counter-acted the fluidizing effect of ethanol.
KW - Anisotropy
KW - Biofuels
KW - Clostridium thermocellum
KW - Consolidated bioprocessing
KW - Ethanol
KW - Fatty acid methyl esters (FAMEs)
KW - Picolinyl esters
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U2 - 10.1007/s00253-009-1891-1
DO - 10.1007/s00253-009-1891-1
M3 - Article
C2 - 19221734
AN - SCOPUS:62949206259
SN - 0175-7598
VL - 82
SP - 929
EP - 939
JO - Applied Microbiology and Biotechnology
JF - Applied Microbiology and Biotechnology
IS - 5
ER -