Lueder Ulf, Maisch Markus, Jørgensen Bo Barker, Druschel Gregory, Schmidt Caroline, Kappler Andreas
Geomicrobiology Group, Center for Applied Geoscience (ZAG), University of Tuebingen, Tuebingen, Germany.
Section for Microbiology, Department of Biology, Aarhus University, Aarhus, Denmark.
Geobiology. 2022 May;20(3):421-434. doi: 10.1111/gbi.12485. Epub 2022 Jan 11.
Iron(II) (Fe(II)) can be formed by abiotic Fe(III) photoreduction, particularly when Fe(III) is organically complexed. Light-influenced environments often overlap or even coincide with oxic or microoxic geochemical conditions, for example, in sediments. So far, it is unknown whether microaerophilic Fe(II)-oxidizing bacteria are able to use the Fe(II) produced by Fe(III) photoreduction as electron donor. Here, we present an adaption of the established agar-stabilized gradient tube approach in comparison with liquid cultures for the cultivation of microaerophilic Fe(II)-oxidizing microorganisms by using a ferrihydrite-citrate mixture undergoing Fe(III) photoreduction as Fe(II) source. We quantified oxygen and Fe(II) gradients with amperometric and voltammetric microelectrodes and evaluated microbial growth by qPCR of 16S rRNA genes. We showed that gradients of dissolved Fe(II) (maximum Fe(II) concentration of 1.25 mM) formed in the gradient tubes when incubated in blue or UV light (400-530 nm or 350-400 nm). Various microaerophilic Fe(II)-oxidizing bacteria (Curvibacter sp. and Gallionella sp.) grew by oxidizing Fe(II) that was produced in situ by Fe(III) photoreduction. Best growth for these species, based on highest gene copy numbers, was observed in incubations using UV light in both liquid culture and gradient tubes containing 8 mM ferrihydrite-citrate mixtures (1:1), due to continuous light-induced Fe(II) formation. Microaerophilic Fe(II)-oxidizing bacteria contributed up to 40% to the overall Fe(II) oxidation within 24 h of incubation in UV light. Our results highlight the potential importance of Fe(III) photoreduction as a source of Fe(II) for Fe(II)-oxidizing bacteria by providing Fe(II) in illuminated environments, even under microoxic conditions.
亚铁（Fe(II)）可通过非生物铁（III）光还原形成，特别是当铁（III）与有机物络合时。受光照影响的环境通常与有氧或微氧地球化学条件重叠甚至重合，例如在沉积物中。到目前为止，尚不清楚微需氧亚铁氧化细菌是否能够利用铁（III）光还原产生的亚铁作为电子供体。在此，我们展示了一种对已建立的琼脂稳定梯度管方法的改进，该方法与液体培养相比，用于培养微需氧亚铁氧化微生物，通过使用经历铁（III）光还原的水铁矿 - 柠檬酸盐混合物作为亚铁源。我们用安培和伏安微电极对氧气和亚铁梯度进行了定量，并通过16S rRNA基因的qPCR评估了微生物生长。我们发现，当在蓝光或紫外光（400 - 530 nm或350 - 400 nm）下孵育时，梯度管中形成了溶解亚铁梯度（最大亚铁浓度为1.25 mM）。各种微需氧亚铁氧化细菌（弯曲杆菌属和嘉利翁氏菌属）通过氧化铁（III）光还原原位产生的亚铁而生长。基于最高基因拷贝数，在液体培养和含有8 mM水铁矿 - 柠檬酸盐混合物（1:1）的梯度管中使用紫外光孵育时，观察到这些物种的最佳生长，这是由于光持续诱导亚铁形成。在紫外光下孵育24小时内，微需氧亚铁氧化细菌对总亚铁氧化的贡献高达40%。我们的结果突出了铁（III）光还原作为亚铁氧化细菌亚铁来源的潜在重要性，即在光照环境中，即使在微氧条件下也能提供亚铁。
