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Diversity of key genes for carbon and nitrogen fixation in soils from the Sor Rondane Mountains, East Antarctica

机译：南极东部Sor Rondane山地土壤固碳和固氮关键基因的多样性

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Although Cyanobacteria are generally considered the most important primary producers and diazotrophs in Antarctic terrestrial ecosystems, in several high-altitude Antarctic regions, they were previously reported to be relatively rare in some samples. In view of these observations, we investigated the presence of non-cyanobacterial carbon- and nitrogen-fixing microorganisms in oligotrophic exposed soils without visible cyanobacterial biomass from the Sor Rondane Mountains, East Antarctica. An Illumina amplicon sequencing approach was used to analyze the bacterial community composition and the diversity and abundance of key genes involved in the carbon- and nitrogen-fixation processes. Analysis of the large subunit of type I ribulose-1,5-biphosphate carboxylase/oxygenase genes (cbbL) revealed a large actinobacterial, and alpha-, beta-, and gammaproteobacterial diversity of CbbL type IC, whereas type IA diversity was restricted to Bradyrhizobium sp.-like sequences. Although a large portion of the CbbL sequences grouped with those of cultivated bacteria, some belonged to currently unknown phylotypes. Data of 16S rRNA genes, however, also revealed that samples contained either considerable numbers of Cyanobacteria or Trebouxiophyceae as oxygenic phototrophic primary producers. Dinitrogenase-reductase genes (nifH) most similar to those of Nostocales cyanobacteria were dominantly retrieved from these oligotrophic soils. These findings suggest that diverse microorganisms capable of assimilating carbon dioxide through the Calvin-Benson-Bassham cycle inhabit these extreme terrestrial systems and potentially may contribute to primary production. However, Cyanobacteria, present in greatly varying numbers as assessed by Illumina amplicon sequencing of a 16S rRNA gene fragment, appear to be the most important nitrogen fixers in these habitats.
机译：尽管蓝细菌通常被认为是南极陆地生态系统中最重要的初级生产者和重氮营养菌，但在一些高海拔南极地区，以前据报道它们在某些样品中相对较少。鉴于这些观察，我们调查了南极东部Sor Rondane山中无营养的暴露于贫营养土壤中的无蓝细菌固碳和固氮微生物的存在。 Illumina扩增子测序方法用于分析细菌群落组成以及参与碳固定和氮固定过程的关键基因的多样性和丰度。对I型核糖-1,5-二磷酸羧化酶/加氧酶基因（cbbL）的大亚基的分析显示，CbbL型IC的放线菌，α，β和γ变形蛋白菌具有较大的多样性，而IA型的多样性仅限于缓生根瘤菌类sp序列。尽管CbbL序列的大部分与栽培细菌的序列分组，但有些属于目前未知的系统型。然而，16S rRNA基因的数据还表明，样品中含有大量的蓝细菌或拟南芥作为氧养光的主要生产者。从这些贫营养土壤中主要回收了与蓝藻细菌最相似的二氮酶还原酶基因（nifH）。这些发现表明，能够通过Calvin-Benson-Bassham循环吸收二氧化碳的多种微生物居住在这些极端的陆地系统中，并可能有助于初级生产。然而，通过Illumina 16S rRNA基因片段的Illumina扩增子测序评估，蓝细菌的数量差异很大，似乎是这些生境中最重要的固氮剂。

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