Investigating the environmental relevance of methoxydotrophic archaea

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Methoxylated aromatic compounds are key components of lignin and coal and are very abundant on Earth. Therefore, it is surprising that conversion of these compounds has previously only been described for bacteria and not for archaea, although the latter have been important drivers of various biogeochemical cycles for billions of years. In 2016, however, it was discovered that the methane-producing archaeon Methermicoccus shengliensis can grow on methoxylated compounds. Methane-producing archaea, so-called methanogens, are major players in the global carbon cycle as well as main producers of the greenhouse gas methane. Therefore, it is crucial to investigate those organisms and to reveal deeper insights into their metabolisms. Using a complementary array of physiological and -omics methods, we showed that M. shengliensis uses a bacteria-like methyl transfer (Mto) system for methanogenesis with methoxylated compounds as substrates and revealed differences in the carbon and energy metabolism compared to the classic pathway using methylated compounds. The discovery of the mto genes enabled us to search for further archaea with the genetic potential to convert methoxylated aromatic compounds. For one of these archaea, the non-methanogenic archaeon Archaeoglobus fulgidus, we could show that this archaeon indeed can grow on methoxylated compounds. Additionally, other archaea such as the hydrogen-utilizing methanogen Methanothermobacter tenebrarum and uncultured archaea such as Verstraetearchaeota appear to have the genetic potential for growth on methoxylated compounds. These findings together with the abundance of methoxylated compounds in natural environments suggest that methoxydotrophic archaea might play an underestimated but vital role for the global carbon cycle. In the proposed project, I intend to investigate the environmental role of methoxydotrophic archaea. We will perform high-throughput sequencing targeting diagnostic genes to survey their distribution and abundance patterns in various habitats such as hydrothermal vents, oil reservoirs or deadwood. Samples with high abundance of methoxydotrophic archaea will be used for enrichment cultures in bottles and in bioreactors to obtain novel isolates. These cultures will further be used to study the ecophysiology of methoxydotrophic archaea, bacteria and potentially fungi present in the cultures by performing RT-qPCR and fluorescence in situ hybridization (FISH) targeting DNA/RNA sequences of genes involved in methoxydotrophic growth as well as metatranscriptomics. Furthermore, novel isolates of methoxydotrophic archaea will be physiologically characterized. This project will provide insights into the methoxydotrophic capabilities of diverse archaea, their exceptional metabolisms alongside with a greater understanding of the role of these archaea in the environment.