Carrasco Naraya, Kretzschmar Ruben, Pesch Marie-Laure, Kraemer Stephan M
Institute of Biogeochemistry and Pollutant Dynamics, Department of Environmental Sciences, ETH Zurich, CHN, CH-8092 Zurich, Switzerland.
Environ Sci Technol. 2007 May 15;41(10):3633-8. doi: 10.1021/es062897r.
Surface-active agents (surfactants) are released by many soil bacteria and plant roots and are also important as environmental contaminants. Their presence at interfaces could influence important biogeochemical processes in soils such as ligand-controlled dissolution, an important process in biological iron acquisition. To investigate their potential influence on ligand-controlled dissolution of iron oxides, we studied the dissolution kinetics of goethite (alpha FeOOH) at pH 6 in the presence of the bacterial siderophore desferrioxamine B (DFOB) and the anionic surfactant sodium dodecyl sulfate (SDS). The adsorption isotherm of SDS on goethite showed an increase in the slope at concentrations ranging between 300 and 400 microM SDS in solution. This increase in slope suggested the onset of admicelle formation. Adsorption of DFOB onto goethite increased strongly with increasing concentrations of adsorbed SDS. Small concentrations of SDS (5 microM) resulted in a 3-fold acceleration of DFOB-controlled goethite dissolution in the presence of 80 microM DFOB, compared to the suspensions without SDS. The effects of SDS on the goethite dissolution rates were less pronounced at higher SDS concentrations, and became negligible above 600 microM total SDS. The dissolution rates of goethite were not proportional to the adsorbed DFOB concentrations, as would be expected for ligand-controlled dissolution. We speculate that increasing concentrations of adsorbed SDS result in a change in DFOB surface speciation from inner-sphere to outer-sphere complexes and, consequently, the ligand-controlled dissolution rates are not linearly related to the adsorbed DFOB concentration. Our results provide the first evidence for an important role of biosurfactants in biological iron acquisition involving siderophores.
许多土壤细菌和植物根系都会释放表面活性剂，并且它们作为环境污染物也很重要。它们在界面处的存在可能会影响土壤中重要的生物地球化学过程，如配体控制的溶解作用，这是生物获取铁的一个重要过程。为了研究它们对氧化铁配体控制溶解的潜在影响，我们研究了在细菌铁载体去铁胺B（DFOB）和阴离子表面活性剂十二烷基硫酸钠（SDS）存在下，针铁矿（α-FeOOH）在pH值为6时的溶解动力学。SDS在针铁矿上的吸附等温线表明，溶液中SDS浓度在300至400微摩尔之间时斜率增加。斜率的增加表明开始形成吸附胶束。随着吸附的SDS浓度增加，DFOB在针铁矿上的吸附强烈增加。与没有SDS的悬浮液相比，在存在80微摩尔DFOB的情况下，低浓度的SDS（5微摩尔）使DFOB控制的针铁矿溶解加速了3倍。在较高的SDS浓度下，SDS对针铁矿溶解速率的影响不太明显，在总SDS浓度高于600微摩尔时可忽略不计。针铁矿的溶解速率与吸附的DFOB浓度不成正比，而配体控制的溶解作用本应如此。我们推测，吸附的SDS浓度增加会导致DFOB表面形态从内球络合物变为外球络合物，因此，配体控制的溶解速率与吸附的DFOB浓度不是线性相关的。我们的结果首次证明了生物表面活性剂在涉及铁载体的生物铁获取中起重要作用。
