Schiessl Konstanze T, Janssen Elisabeth M-L, Kraemer Stephan M, McNeill Kristopher, Ackermann Martin
Department of Environmental Systems Science, Institute of Biogeochemistry and Pollutant Dynamics, Swiss Federal Institute of Technology, Zurich, Switzerland.
Department of Environmental Microbiology, Swiss Federal Institute of Aquatic Science and Technology, Dübendorf, Switzerland.
Front Microbiol. 2017 Oct 10;8:1964. doi: 10.3389/fmicb.2017.01964. eCollection 2017.
A central question in microbial ecology is whether microbial interactions are predominantly cooperative or competitive. The secretion of siderophores, microbial iron chelators, is a model system for cooperative interactions. However, siderophores have also been shown to mediate competition by sequestering available iron and making it unavailable to competitors. The details of how siderophores mediate competition are not well understood, especially considering the complex distribution of iron phases in the environment. One pertinent question is whether sequestering iron through siderophores can indeed be effective in natural conditions; many natural environments are characterized by large pools of precipitated iron, and it is conceivable that any soluble iron that is sequestered by siderophores is replenished by the dissolution of these precipitated iron sources. Our goal here was to address this issue, and investigate the magnitude and mechanism of siderophore-mediated competition in the presence of precipitated iron. We combined experimental work with thermodynamic modeling, using as a model system and ferrihydrite precipitates as the iron source with low solubility. Our experiments show that competitive growth inhibition by the siderophore pyochelin is indeed efficient, and that inhibition of a competitor can even have a stronger growth-promoting effect than solubilization of precipitated iron. Based on the results of our thermodynamic models we conclude that the observed inhibition of a competitor is effective because sequestered iron is only very slowly replenished by the dissolution of precipitated iron. Our research highlights the importance of competitive benefits mediated by siderophores, and underlines that the dynamics of siderophore production and uptake in environmental communities could be a signature of competitive, not just cooperative, dynamics.
微生物生态学中的一个核心问题是，微生物间的相互作用主要是合作性的还是竞争性的。铁载体（微生物铁螯合剂）的分泌是合作性相互作用的一个模型系统。然而，铁载体也已被证明可通过螯合可利用的铁并使其竞争对手无法获取来介导竞争。铁载体介导竞争的具体细节尚未得到很好的理解，尤其是考虑到环境中铁相的复杂分布。一个相关问题是，通过铁载体螯合铁在自然条件下是否真的有效；许多自然环境的特征是存在大量沉淀铁，可想而知，铁载体螯合的任何可溶性铁都会因这些沉淀铁源的溶解而得到补充。我们这里的目标是解决这个问题，并研究在存在沉淀铁的情况下铁载体介导竞争的程度和机制。我们将实验工作与热力学建模相结合，以绿脓菌素作为模型系统，以低溶解度的水铁矿沉淀作为铁源。我们的实验表明，铁载体绿脓菌素对生长的竞争性抑制确实有效，而且对竞争对手的抑制甚至可能比沉淀铁的溶解具有更强的促进生长作用。基于我们热力学模型的结果，我们得出结论，观察到的对竞争对手的抑制是有效的，因为沉淀铁的溶解只能非常缓慢地补充被螯合的铁。我们的研究突出了铁载体介导的竞争优势的重要性，并强调环境群落中铁载体产生和摄取的动态可能是竞争性动态的标志，而不仅仅是合作性动态的标志。
