Nikeleit Verena, Maisch Markus, Straub Daniel, Eroglu Sümeyya, Lopez-Rivoldi Jimena C, Strauss Harald, Ring-Hrubesh Fin, Byrne James M, Kappler Andreas, Bryce Casey
Department of Geoscience, University of Tübingen, 72076 Tübingen, Germany.
now: NORCE Norwegian Research Center AS, 5008 Bergen, Norway.
FEMS Microbiol Ecol. 2025 Mar 18;101(4). doi: 10.1093/femsec/fiaf029.
Iron cycling including phototrophic Fe(II) oxidation has been observed in multiple permanently stratified meromictic lakes, yet less focus has been on dimictic lakes, which seasonally overturn and are vastly more common. Here, we investigated iron cycling in a dimictic lake, Großes Heiliges Meer in northwest Germany, using 16S rRNA amplicon sequencing, as well as in-situ and lab-based experiments. Bacterial community composition in the lake follows geochemical gradients and differs markedly between oxic and anoxic conditions. Potential iron-metabolizing bacteria were found mostly in anoxic conditions at 7 and 8 m depth and were comprised of taxa from the genera Chlorobium, Thiodictyon, Sideroxydans, Geobacter, and Rhodoferrax. We were able to recreate active iron cycling (1) with an ex-situ microbial community from 8 m depth and (2) with a successful microbial enrichment culture from 7 m depth. Varying the light and organic carbon availability in lab-based experiments showed that Fe(III) reduction overshadows Fe(II) oxidation leading to a cryptic iron cycle. Overall, we could demonstrate that microbial iron cycling can be a key biogeochemical process in dimictic lakes despite regular disturbance, and that complex environmental factors such as organic substrates control the balance between Fe(II) oxidation and Fe(III) reduction.
包括光养铁（II）氧化在内的铁循环已在多个永久性分层的半混合湖中被观测到，但对季节翻转且更为常见的双季湖的关注较少。在此，我们利用16S rRNA扩增子测序以及原位和实验室实验，对德国西北部的双季湖大神圣湖的铁循环进行了研究。该湖中的细菌群落组成遵循地球化学梯度，在有氧和无氧条件下有显著差异。潜在的铁代谢细菌大多存在于7至8米深度的无氧条件下，包括绿菌属、网硫菌属、嗜铁氧化菌属、地杆菌属和红铁杆菌属的分类群。我们能够（1）用来自8米深度的异位微生物群落以及（2）用来自7米深度的成功的微生物富集培养物重建活跃的铁循环。在实验室实验中改变光照和有机碳的可利用性表明，铁（III）还原超过铁（II）氧化，导致一个隐秘的铁循环。总体而言，我们能够证明，尽管有定期干扰，微生物铁循环仍是双季湖中的一个关键生物地球化学过程，并且诸如有机底物等复杂环境因素控制着铁（II）氧化和铁（III）还原之间的平衡。
