Ehrl Benno N, Gharasoo Mehdi, Elsner Martin
Institute of Groundwater Ecology , Helmholtz Zentrum München , Ingolstädter Landstrasse 1 , 85764 Neuherberg , Germany.
Chair of Analytical Chemistry and Water Chemistry , Technical University of Munich , Marchioninistrasse 17 , 81377 Munich , Germany.
Environ Sci Technol. 2018 Apr 3;52(7):4137-4144. doi: 10.1021/acs.est.7b06599. Epub 2018 Mar 23.
Biodegradation of persistent pesticides like atrazine often stalls at low concentrations in the environment. While mass transfer does not limit atrazine degradation by the Gram-positive Arthrobacter aurescens TC1 at high concentrations (>1 mg/L), evidence of bioavailability limitations is emerging at trace concentrations (<0.1 mg/L). To assess the bioavailability constraints on biodegradation, the roles of cell wall physiology and transporters remain imperfectly understood. Here, compound-specific isotope analysis (CSIA) demonstrates that cell wall physiology (i.e., the difference between Gram-negative and Gram-positive bacteria) imposes mass transfer limitations in atrazine biodegradation even at high concentrations. Atrazine biodegradation by Gram-negative Polaromonas sp. Nea-C caused significantly less isotope fractionation (ε(C) = -3.5 ‰) than expected for hydrolysis by the enzyme TrzN (ε(C) = -5.0 ‰) and observed in Gram-positive Arthrobacter aurescens TC1 (ε(C) = -5.4 ‰). Isotope fractionation was recovered in cell-free extracts (ε(C) = -5.3 ‰) where no cell envelope restricted pollutant uptake. When active transport was inhibited with cyanide, atrazine degradation rates remained constant demonstrating that atrazine mass transfer across the cell envelope does not depend on active transport but is a consequence of passive cell wall permeation. Taken together, our results identify the cell envelope of the Gram-negative bacterium Polaromonas sp. Nea-C as a relevant barrier for atrazine biodegradation.
像阿特拉津这样的持久性农药在环境中的生物降解在低浓度时往往会停滞不前。虽然在高浓度（>1毫克/升）下传质并不限制革兰氏阳性金色节杆菌TC1对阿特拉津的降解，但在痕量浓度（<0.1毫克/升）下生物可利用性限制的证据正在显现。为了评估生物降解的生物可利用性限制，细胞壁生理学和转运蛋白的作用仍未得到充分理解。在这里，化合物特异性同位素分析（CSIA）表明，即使在高浓度下，细胞壁生理学（即革兰氏阴性菌和革兰氏阳性菌之间的差异）也会对阿特拉津的生物降解造成传质限制。革兰氏阴性极地单胞菌Nea-C对阿特拉津的生物降解所导致的同位素分馏（ε(C)= -3.5‰）明显低于酶TrzN水解预期的分馏（ε(C)= -5.0‰），也低于在革兰氏阳性金色节杆菌TC1中观察到的分馏（ε(C)= -5.4‰）。在无细胞提取物中恢复了同位素分馏（ε(C)= -5.3‰），在这种情况下没有细胞包膜限制污染物的吸收。当用氰化物抑制主动转运时，阿特拉津的降解速率保持不变，这表明阿特拉津跨细胞包膜的传质不依赖于主动转运，而是被动细胞壁渗透的结果。综上所述，我们的结果确定革兰氏阴性细菌极地单胞菌Nea-C的细胞包膜是阿特拉津生物降解的一个相关屏障。
