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

点击翻译按钮获取中文摘要

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.