Environmental Controls of Iron-Reducing Microorganisms in Antarctic Marine Sediments [ECIMAS]

气候变化导致南极半岛西部冰川融化速度加快。因此，在包括波特湾在内的地区，陆架沉积物积累增加，包括大量活性氧化铁。沉积物上层的高溶解铁浓度表明微生物铁还原是主要的厌氧呼吸过程。在ECIMAS的前一阶段，我们发现微生物铁还原强烈受温度变化和不稳定有机碳的可用性的影响。然而，硫酸盐还原微生物占波特湾沉积物中微生物群落的30%以上，甚至在富含铁的冰川附近也出乎意料。这是令人惊讶的，因为沉积物深度的硫酸盐分布基本不变，表明硫酸盐消耗有限。此外，铁还原微生物占主导地位的稳定同位素探测（SIP）的实验进行了13 C-乙酸，这是一个典型的基板也明显无活性，但在原位高度丰富的硫酸盐还原微生物。因此，它仍然是不受约束的基板是控制厌氧呼吸微生物，包括铁和硫酸盐还原微生物在南极波特湾沉积物的中心。因此，为了扩展我们的ECIMAS项目，我们将集中精力确定原位微生物积极使用的底物。我们的方法包括两个相互依赖的步骤：（i）首先，我们将通过原位沉积物群落的宏转录组分析结合宏基因组序列分析（> 1000 Gbp）来跟踪微生物活动，这是高频率匹配转录本所需的。强表达的代谢途径将反映在这些原位样品中最丰富的基因转录本中。(ii)反过来，这些鉴定的途径将用于靶向RNA-SIP孵育中铁和硫酸盐还原剂的可能重要底物，从而验证观察到的原位基因表达、微生物丰度模式以及活性铁和硫酸盐还原微生物的身份。我们的组学方法将允许区分基板作为有利于铁还原微生物的环境因素，而波特湾沉积物中已知的硫酸盐还原菌的常备库存似乎得到维持。这反过来将有助于了解这两个进口组的厌氧呼吸微生物在极地沉积物中共存的潜在机制。

Climate change has resulted in an accelerated rate of glacier melting in the western Antarctic Peninsula. As a consequence for the area including Potter Cove, shelf sediment accumulation has increased including that of large amounts of reactive iron oxide. High dissolved iron concentration in upper sediment layers point to microbial iron reduction as dominant anaerobic respiratory process. In the preceding phase of ECIMAS, we found microbial iron reduction strongly affected by changes in temperature, and availability of labile organic carbon. Yet, sulfate reducing microorganisms make up over 30% of the microbial community in Potter Cove sediments, and unexpectedly even in iron-rich glacier proximal sites. This is surprising as sulfate profiles over sediment depths are largely invariable there suggesting limited sulfate consumption. Moreover, iron-reducing microorganisms were dominating in stable isotope probing (SIP) experiment conducted with 13C-acetate, which is a canonical substrate also for the apparently inactive but in-situ highly abundant sulfate-reducing microorganisms. Thus, it is still unconstrained which substrates are central for controlling anaerobically respiring microorganisms including iron and sulfate -reducing microorganisms in Antarctic Potter Cove sediment. For the extension of our ECIMAS project, we will therefore concentrate on identifying substrates that are actively used by microorganisms in-situ. Our approach comprises of two interdependent steps: (i) Firstly, we will track microbial activities by metatranscriptome analysis of in-situ sediment communities combined with metagenome sequence analysis (> 1000 Gbp) required for matching transcripts at high frequency. Strongly expressed metabolic pathways will be reflected in the most abundant gene transcripts from these in-situ samples. (ii) In turn, these identified pathways will be used to target likely important substrates for iron- and sulfate reducers in RNA-SIP incubations, thereby verifying observed in-situ gene expression, microbial abundance patterns, and the identity of active iron- and sulfate reducing microorganisms. Our omics approach will allow discriminating substrates as environmental factor that favor iron reducing microorganisms, while a standing stock of known sulfate reducing bacteria in Potter Cove sediments seems to be maintained. This in turn will help to understand the underlying mechanism of coexistence of these tow import groups of anaerobically respiring microorganisms in polar sediments.