Nybroe Ole, Brandt Kristian K, Ibrahim Yusuf M, Tom-Petersen Andreas, Holm Peter E
Department of Ecology, Faculty of Life Sciences, University of Copenhagen, Thorvaldsensvej 40, DK-1871 Frederiksberg C, Denmark.
Environ Toxicol Chem. 2008 Nov;27(11):2246-52. doi: 10.1897/08-025.1.
Increased levels of Cu in agricultural soils are of concern, because Cu toxicity may adversely affect important soil microorganisms, including pseudomonads. Because total metal concentrations correlate poorly with bioavailability and toxicity, a need exists for more information linking Cu speciation, bioavailability, and toxicity. The objective of the present study was to determine the bioavailability of different Cu complexes to Pseudomonas spp. A Cu-specific bioluminescent Pseudomonas fluorescens reporter strain was used to determine bioavailable Cu, which was operationally defined as those Cu species that induced expression of bioluminescence. Another strain of P. fluorescens, which continuously expressed bioluminescence, was used as a toxicity reporter. Experiments were performed in a defined aqueous medium containing 0.04 microM Cu, which was amended with ethylenediaminetetraacetic acid (EDTA), citrate, or a well-characterized pool of dissolved organic matter (DOM). Bioluminescence emitted by the biosensors was related to data for Cu speciation obtained by geochemical modeling. Changes in Cu bioavailability in the presence of EDTA coincided with modeled changes in Cu2+ activity, indicating that Cu-EDTA complexes were not bioavailable to the Cu-specific reporter. In contrast, changes of Cu bioavailability in the presence of citrate did not correspond to changes in Cu2+, indicating that Cu-citrate complexes were fully bioavailable to the reporter strain. Finally, the response of the Cu-reporter strain to Cu in the presence of DOM indicated that Cu formed bioavailable as well as unavailable complexes with DOM. We conclude that free Cu2+ activity is a poor predictor of Cu bioavailability to Pseudomonas spp. in samples containing organic ligands.
农业土壤中铜含量的增加令人担忧，因为铜毒性可能会对包括假单胞菌在内的重要土壤微生物产生不利影响。由于总金属浓度与生物有效性和毒性的相关性较差，因此需要更多有关铜形态、生物有效性和毒性之间联系的信息。本研究的目的是确定不同铜络合物对假单胞菌属的生物有效性。使用一种对铜具有特异性的生物发光荧光假单胞菌报告菌株来测定生物可利用铜，其在操作上被定义为那些诱导生物发光表达的铜物种。另一种持续表达生物发光的荧光假单胞菌菌株被用作毒性报告菌株。实验在含有0.04微摩尔铜的特定水性介质中进行，该介质用乙二胺四乙酸（EDTA）、柠檬酸盐或一组特征明确的溶解有机物（DOM）进行了修正。生物传感器发出的生物发光与通过地球化学模型获得的铜形态数据相关。在EDTA存在下铜生物有效性的变化与模拟的Cu2+活性变化一致，表明Cu-EDTA络合物对铜特异性报告菌株无生物可利用性。相比之下，在柠檬酸盐存在下铜生物有效性的变化与Cu2+的变化不对应，表明铜-柠檬酸盐络合物对报告菌株具有完全生物可利用性。最后，铜报告菌株在DOM存在下对铜的反应表明，铜与DOM形成了生物可利用和不可利用的络合物。我们得出结论，在含有有机配体的样品中，游离Cu2+活性不能很好地预测铜对假单胞菌属的生物有效性。
