Mancini Silvia A, Hirschorn Sarah K, Elsner Martin, Lacrampe-Couloume Georges, Sleep Brent E, Edwards Elizabeth A, Lollar Barbara Sherwood
Stable Isotope Laboratory, Department of Geology, University of Toronto, 22 Russell Street, Toronto, Canada M5S 3B12.
Environ Sci Technol. 2006 Dec 15;40(24):7675-81. doi: 10.1021/es061363n.
The effects of iron concentration on carbon and hydrogen isotopic fractionation during aerobic biodegradation of toluene by Pseudomonas putida mt-2 were investigated using a low iron medium and two different high iron media. Mean carbon enrichment factors (epsilonc) determined using a Rayleigh isotopic model were smaller in culture grown under high iron conditions (epsilonc = -1.7+/-0.1%) compared to low iron conditions (epsilonc = -2.5+/-0.3%). Mean hydrogen enrichment factors (epsilonH) were also significantly smaller for culture grown under high iron conditions (epsilonH = -77 +/-4%) versus low iron conditions (EpsilonH = -159+/-11%). A mechanistic model for enzyme kinetics was used to relate differences in the magnitude of isotopic fractionation for low iron versus high iron cultures to the efficiency of the enzymatic transformation. The increase of carbon and hydrogen enrichment factors at low iron concentrations suggests a slower enzyme-catalyzed substrate conversion step (k2) relative to the enzyme-substrate binding step (k-l) at low iron concentration. While the observed differences were subtle and, hence, do not significantly impact the ability to use stable isotope analysis in the field, these results demonstrated that resolvable differences in carbon and hydrogen isotopic fractionation were related to low and high iron conditions. This novel result highlights the need to further investigate the effects of other trace elements known to be key components of biodegradative enzymes.
利用低铁培养基和两种不同的高铁培养基，研究了铁浓度对恶臭假单胞菌mt-2好氧生物降解甲苯过程中碳和氢同位素分馏的影响。使用瑞利同位素模型确定的平均碳富集因子（εc）在高铁条件下培养的菌株中较小（εc = -1.7±0.1%），而在低铁条件下培养的菌株中较大（εc = -2.5±0.3%）。平均氢富集因子（εH）在高铁条件下培养的菌株中也显著较小（εH = -77±4%），而在低铁条件下培养的菌株中较大（εH = -159±11%）。使用酶动力学的机理模型将低铁与高铁培养物中同位素分馏幅度的差异与酶促转化效率联系起来。低铁浓度下碳和氢富集因子的增加表明，相对于低铁浓度下的酶-底物结合步骤（k-1），酶催化的底物转化步骤（k2）较慢。虽然观察到的差异很细微，因此不会显著影响在现场使用稳定同位素分析的能力，但这些结果表明，碳和氢同位素分馏中可分辨的差异与低铁和高铁条件有关。这一新颖的结果凸显了进一步研究已知为生物降解酶关键成分的其他微量元素影响的必要性。
