Metagenomic insights into diazotrophic communities across Arctic glacier forefields

Author(s): Nash, MV; Anesio, AM; Barker, G; Tranter, M; Varliero, G; Eloe-Fadrosh, EA; Nielsen, T; Turpin-Jelfs, T; Benning, LG; Sanchez-Baracaldo, P | Abstract: © FEMS 2018. Microbial nitrogen fixationis crucial for building labile nitrogen stocks and facilitating higher plant colonisation in oligotrophic glacier forefield soils. Here, the diazotrophicbacterial community structure across four Arctic glacier forefields was investigated using metagenomicanalysis. In total, 70 soil metagenomeswere used for taxonomic interpretation based on 185 nitrogenase(nif) sequences, extracted from assembled contigs. The low number of recovered genes highlights the need for deeper sequencing in some diverse samples, to uncover the complete microbial populations. A key group of forefield diazotrophs, found throughout the forefields, was identified using a nifH phylogeny, associated with nifH Cluster I and III. Sequences related most closely to groups including Alphaproteobacteria, Betaproteobacteria, Cyanobacteria and Firmicutes. Using multiple nif genesin a Last Common Ancestor analysis revealed a diverse range of diazotrophsacross the forefields. Key organisms identified across the forefields included Nostoc, Geobacter, Polaromonasand Frankia. Nitrogen fixers that are symbiotic with plants were also identified, through the presence of root associated diazotrophs, which fix nitrogen in return for reduced carbon. Additionalnitrogen fixers identified in forefield soils were metabolically diverse, including fermentative and sulphur cycling bacteria, halophilesand anaerobes.