Biogeography and Phylogeny of Aigarchaeota, A Novel Phylum of Archaea
Despite our knowledge of the diversity of life on earth there are major lineages of microbial life that have never been studied that are referred to as “biological dark matter” or “microbial dark matter” (Marcy et al., 2007; Rinke, et al., 2013). One of these so-called “microbial dark matter” groups was originally described as pSL4 and related gene sequences were later grouped under the name Hot Water Crenarchaeotic Group 1 (HWCG 1) (Barns et al., 1996; Nunoura et al., 2005). A metagenomics study of a microbial mat community led to the construction of a complete composite genome for a member of the pSL4/HWCG 1 lineage proposed as Candidatus ‘Caldiarchaeum subterraneum’ and further analysis of the genome led to the proposition of the phylum ‘Aigarchaeota’ (Nunoura et al., 2005; Nunoura et al., 2011). Genomic analysis of Ca. subterraneum revealed unique eukaryote-type features which led to the proposal of a superphylum level relationship called the ‘TACK’ superphylum (Guy and Ettema, 2011). The cultivationindependent studies suggest a world-wide distribution of ‘Aigarchaeota’ and dominance of 16S rRNA gene clone libraries from habitats such as a deep sea hydrothermal vent in Okinawa Trough at 35-60 °C and Great Boiling Spring at 79-87°C ( Nunoura et al., 2010; Cole et al., 2012). Cole at al 2012 reported that ‘Aigarchaeota’ 16S rRNA gene sequences had the highest relative abundance at Site A (~54%), with a general trend of decreasing relative abundance down to ~5% at 62°C (Site E), suggesting ‘Aigarchaeota’ niche differentiation along a thermal gradient. The purpose of this study was to gather 16S rRNA gene sequences potentially belonging to ‘Aigarchaeota’, and to use those sequences to address several goals: (i) Rigorously define the phylum (ii) Gain insight into the phylogenetic and potential taxonomic structure of the phylum (iii) Assess the distribution of ‘Aigarchaeota’ as a whole, along with individual groups of ‘Aigarchaeota’ in nature (iv) Design ‘Aigarchaeota’specific 16S rRNA gene primers that combined will target genus-level groups