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Diversification of methanogens into hyperalkaline serpentinizing environments through adaptations to minimize oxidant limitation
The ISME Journal ( IF 11.0 ) Pub Date : 2020-11-30 , DOI: 10.1038/s41396-020-00838-1
Elizabeth M Fones 1 , Daniel R Colman 1 , Emily A Kraus 2 , Ramunas Stepanauskas 3 , Alexis S Templeton 4 , John R Spear 2 , Eric S Boyd 1
Affiliation  

Metagenome assembled genomes (MAGs) and single amplified genomes (SAGs) affiliated with two distinct Methanobacterium lineages were recovered from subsurface fracture waters of the Samail Ophiolite, Sultanate of Oman. Lineage Type I was abundant in waters with circumneutral pH, whereas lineage Type II was abundant in hydrogen rich, hyperalkaline waters. Type I encoded proteins to couple hydrogen oxidation to CO2 reduction, typical of hydrogenotrophic methanogens. Surprisingly, Type II, which branched from the Type I lineage, lacked homologs of two key oxidative [NiFe]-hydrogenases. These functions were presumably replaced by formate dehydrogenases that oxidize formate to yield reductant and cytoplasmic CO2 via a pathway that was unique among characterized Methanobacteria, allowing cells to overcome CO2/oxidant limitation in high pH waters. This prediction was supported by microcosm-based radiotracer experiments that showed significant biological methane generation from formate, but not bicarbonate, in waters where the Type II lineage was detected in highest relative abundance. Phylogenetic analyses and variability in gene content suggested that recent and ongoing diversification of the Type II lineage was enabled by gene transfer, loss, and transposition. These data indicate that selection imposed by CO2/oxidant availability drove recent methanogen diversification into hyperalkaline waters that are heavily impacted by serpentinization.



中文翻译:

通过适应最大限度地减少氧化剂限制,使产甲烷菌多样化进入高碱性蛇纹石化环境

从阿曼苏丹国 Samail 蛇绿岩的地下裂缝水中回收了与两个不同的甲烷杆菌谱系相关的宏基因组组装基因组 (MAG) 和单一扩增基因组 (SAG) 。I 型谱系在 pH 值接近中性的水域中含量丰富,而 II 型谱系在富含氢的高碱性水中含量丰富。I 型编码蛋白将氢氧化与 CO 2还原偶联,这是典型的氢营养型产甲烷菌。令人惊讶的是,从 I 型谱系分支出来的 II 型缺乏两种关键氧化性 [NiFe]-氢化酶的同系物。这些功能可能被甲酸脱氢酶取代,甲酸脱氢酶氧化甲酸产生还原剂和细胞质 CO 2通过在特征化的甲烷菌中独一无二的途径,使细胞能够克服高 pH 水中的 CO 2 /氧化剂限制。这一预测得到了基于微观世界的放射性示踪剂实验的支持,该实验表明在以最高相对丰度检测到 II 型谱系的水域中,甲酸盐而非碳酸氢盐会产生大量生物甲烷。系统发育分析和基因含量的变异性表明,最近和正在进行的 II 型谱系的多样化是由基因转移、丢失和转座实现的。这些数据表明,由 CO 2 /氧化剂可用性强加的选择促使最近的产甲烷菌多样化进入受蛇纹石化严重影响的超碱性水域。

更新日期:2020-12-01
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