Metagenomic analysis of extreme environments in astrobiology: understanding the evolution of primitive life

Metagenomic analysis applied to specialized environments offers the possibility to understand the evolution of complex biotypes. In particular, metagenomics of extreme environments, which might resemble those of primitive Earth, is of interest for the study of the origin, evolution and distribution of extremophiles (organisms thriving at these conditions) as primitive forms of life populating our planet and, in an astrobiological perspective, other bodies in the universe. The Pisciarelli solfatara, located in the Phelgrean Fields (Naples, Italy), is characterized by a remarkable diversity in terms of temperature and pHs of the different mud pools and solfataric vents [1]. Here several thermoacidophilic species, such as Acidianus, Archaeoglobus spp, Pyrobaculum, Sulfolobus, and several viruses have been isolated [1]. In order to map the composition of this biotope in terms of number and abundance of the different species, we decided to carry out a metagenomic deep sequencing project on soil and water/mud pools of Pisciarelly solfatara. We will show our preliminary results derived by the sampling in the main water pool. Total DNA was extracted from the pellets obtained by centrifuging water samples and analysed by using Illumina paired-end sequencing technology. In a single run, we produced~3.0 Gb total nucleotides. These reads were assembled into 1,543 contigs with an N50 of 15863 bp，and a total of 17,652 Open Reading Frames (ORFs) were identified. These ORFs were subjected to BLAST similarity searches and annotated with KEGG, eggNOG and NR database respectively. The clean reads rate was 99.7% and a total of 17,652 Open Reading Frames (ORFs) were identified. The majority (77%) of the species found belonged to the Crenarcheaota phylum, which branches deeply in the phylogenetic tree of life, followed by Proteobacteria (22%), and, in much lesser amounts, Euryarchaeota, Actinobacteria, and others. The number of species identified is much higher than those found by a conventional PCR-based approach [2]. Details on the species composition and on the realtive abundance of each ORF will be described together with the astrobiological implications.