Romano Stefano, Bondarev Vladimir, Kölling Martin, Dittmar Thorsten, Schulz-Vogt Heide N
Max Planck Institute for Marine Microbiology, Bremen, Germany.
Marum Center for Marine Environmental Sciences, Bremen, Germany.
Front Microbiol. 2017 Mar 14;8:364. doi: 10.3389/fmicb.2017.00364. eCollection 2017.
Phosphorus is an essential nutrient for all living organisms. In bacteria, the preferential phosphorus source is phosphate, which is often a limiting macronutrient in many areas of the ocean. The geochemical cycle of phosphorus is strongly interconnected with the cycles of other elements and especially iron, because phosphate tends to adsorb onto iron minerals, such as iron oxide formed in oxic marine environments. Although the response to either iron or phosphate limitation has been investigated in several bacterial species, the metabolic interplay between these two nutrients has rarely been considered. In this study we evaluated the impact of phosphate limitation on the iron metabolism of the marine bacterium sp. FO-BEG1. We observed that phosphate limitation led to an initial decrease of soluble iron in the culture up to three times higher than under phosphate surplus conditions. Similarly, a decrease in soluble cobalt was more pronounced under phosphate limitation. These data point toward physiological changes induced by phosphate limitation that affect either the cellular surface and therefore the metal adsorption onto it or the cellular metal uptake. We discovered that under phosphate limitation strain FO-BEG1, as well as selected strains of the clade, secreted iron-chelating molecules. This leads to the hypothesis that these bacteria might release such molecules to dissolve iron minerals, such as iron-oxyhydroxide, in order to access the adsorbed phosphate. As the adsorption of phosphate onto iron minerals can significantly decrease phosphate concentrations in the environment, the observed release of iron-chelators might represent an as yet unrecognized link between the biogeochemical cycle of phosphorus and iron, and it suggests another biological function of iron-chelating molecules in addition to metal-scavenging.
磷是所有生物必需的营养物质。在细菌中，优先的磷源是磷酸盐，而磷酸盐在海洋的许多区域通常是一种限制性常量营养素。磷的地球化学循环与其他元素的循环，尤其是铁的循环紧密相连，因为磷酸盐倾向于吸附在铁矿物上，比如在有氧海洋环境中形成的氧化铁。尽管已经在几种细菌物种中研究了对铁或磷酸盐限制的反应，但这两种营养素之间的代谢相互作用很少被考虑。在本研究中，我们评估了磷酸盐限制对海洋细菌sp. FO-BEG1铁代谢的影响。我们观察到，磷酸盐限制导致培养物中可溶性铁最初减少，减少量比磷酸盐过剩条件下高出三倍。同样，在磷酸盐限制下，可溶性钴的减少更为明显。这些数据表明，磷酸盐限制引起了生理变化，这些变化影响细胞表面，进而影响金属在其上的吸附或细胞对金属的摄取。我们发现，在磷酸盐限制下，菌株FO-BEG1以及进化枝的选定菌株会分泌铁螯合分子。这就引出了一个假设，即这些细菌可能释放此类分子来溶解铁矿物，如羟基氧化铁，以便获取吸附在其上的磷酸盐。由于磷酸盐在铁矿物上的吸附会显著降低环境中的磷酸盐浓度，观察到的铁螯合剂释放可能代表了磷和铁生物地球化学循环之间一个尚未被认识的联系，这也表明铁螯合分子除了具有金属清除功能外还有另一种生物学功能。
