Nitrate-reducing Fe(II)-oxidizing microorganisms in a geochemical and mineralogical Mars terrestrial analogue (Rio Tinto, Spain)

在火星盖尔陨石坑发现的含铁（II）和硝酸盐的矿物表明，硝酸盐还原铁（II）氧化（NRFeOx）微生物可能是早期火星河湖系统的初级生产者，并可能在行星表面干燥后很长时间内一直存在于地下含水层中。这样的环境在早期的Hesperian Eon受到的物理化学变化，如周期性的干燥，盐度，pH值的变化，等在这种环境中NRFeOx微生物可以参与N和Fe循环导致形成气态氮物种，Fe（III）（oxyhydr）氧化物和Fe（III）羟基硫酸盐矿物。类似的Fe（III）矿物丰富的生物圈的物理化学波动的特点是典型的陆地河口系统受酸性矿山排水。例如，Rio Tinto河（西班牙）河口的潮汐活动调节了pH值、Eh、盐度等的波动，而旱季则导致河口周围洪泛平原的干燥。在这个独特的缺氧生物圈中的初级生产可以通过化学合成NRFeOx活性来支持。这种可能性对于假设的火星表面干燥后的生命具有至关重要的价值。因此，本提案的第一个目标是从河口和河流源头的富铁缺氧沉积物中分离NRFeOx微生物，并从Rio Tinto地区收集的地下岩心样品中分离NRFeOx微生物。第二个目标是鉴定和表征NRFeOx微生物的分离菌株。第三个目标是评估它们的代谢活性和对Fe（II）矿物氧化、初级生产和N2O形成的贡献。这些目标将通过地球化学、生理学和分子方法的结合来实现，包括宏基因组学和元转录组学。该项目的结果将有助于我们揭示i）河口和源头以及Rio Tinto地区深层次表层沉积物中NRFeOx微生物的环境生态位和作用，ii）栖息在河口和源头沉积物和次表层岩石中的NRFeOx微生物的代谢特征，和iii）假设的NRFeOx微生物的生存能力，以支持使用类似于在火星上发现的含Fe（II）的矿物的生长。

The identification of Fe(II)- and nitrate-containing minerals at the Gale crater on Mars suggested that nitrate-reducing Fe(II)-oxidizing (NRFeOx) microorganisms could have acted as primary producers in early Martian fluvio-lacustrine systems and could have persisted in subsurface aquifers long after the desiccation of the planetary surface. Such an environment during the early Hesperian Eon was subjected to physio-chemical variations such as periodical desiccation, changes in salinity, pH, etc. In this environment NRFeOx microorganisms could participate in N and Fe cycles resulting in formation of gaseous nitrogen species, Fe(III) (oxyhydr)oxide and Fe(III) hydroxysulfate minerals. Analogous Fe(III) mineral-rich biospheres characterized by physico-chemical fluctuations are typical for terrestrial estuarine systems affected by acid mine drainage. For example, the tidal activity in the estuary of the Rio Tinto river (Spain) modulates fluctuations in pH, Eh, salinity, etc. while dry seasons lead to desiccation of floodplains surrounding the estuary. The primary production in this unique anoxic biosphere can be supported by chemosynthetic NRFeOx activity. This possibility could have a crucial value for hypothetical Martian life after desiccation of the surface. Therefore, the first goal of the present proposal is to isolate NRFeOx microorganisms from anoxic Fe(II)-rich sediments at the estuary and headwaters of the river and from subsurface core samples collected in the Rio Tinto region. The second goal is to identify and characterize the isolated strains of NRFeOx microorganisms. The third goal is to evaluate their metabolic activity and contribution to Fe(II) mineral oxidation, primary production and N2O formation. These goals will be achieved by a combination of geochemical, physiological and molecular approaches, including metagenomics and metatranscriptomics. The results from this project will help us to reveal i) the environmental niches and the role of NRFeOx microorganisms in sediments of the estuary and headwaters as well as in the deep subsurface of the Rio Tinto region, ii) the metabolic characteristics of NRFeOx microorganisms inhabiting the estuary and headwater sediments and subsurface rock, and iii) the hypothetical viability of NRFeOx microorganisms to support growth using Fe(II)-bearing minerals similar to those that were found on Mars.