title: New insights into marine group III Euryarchaeota, from dark to light.
abstract: Marine Euryarchaeota remain among the least understood major components of marine microbial communities. Marine group II Euryarchaeota (MG-II) are more abundant in surface waters (4-20% of the total prokaryotic community), whereas marine group III Euryarchaeota (MG-III) are generally considered low-abundance members of deep mesopelagic and bathypelagic communities. Using genome assembly from direct metagenome reads and metagenomic fosmid clones, we have identified six novel MG-III genome sequence bins from the photic zone (Epi1-6) and two novel bins from deep-sea samples (Bathy1-2). Genome completeness in those genome bins varies from 44% to 85%. Photic-zone MG-III bins corresponded to novel groups with no similarity, and significantly lower GC content, when compared with previously described deep-MG-III genome bins. As found in many other epipelagic microorganisms, photic-zone MG-III bins contained numerous photolyase and rhodopsin genes, as well as genes for peptide and lipid uptake and degradation, suggesting a photoheterotrophic lifestyle. Phylogenetic analysis of these photolyases and rhodopsins as well as their genomic context suggests that these genes are of bacterial origin, supporting the hypothesis of an MG-III ancestor that lived in the dark ocean. Epipelagic MG-III occur sporadically and in relatively small proportions in marine plankton, representing only up to 0.6% of the total microbial community reads in metagenomes. None of the reconstructed epipelagic MG-III genomes were present in metagenomes from aphotic zone depths or from high latitude regions. Most low-GC bins were highly enriched at the deep chlorophyll maximum zones, with the exception of Epi1, which appeared evenly distributed throughout the photic zone worldwide.
authors.affiliation: Evolutionary Genomics Group, Departamento de Producción Vegetal y Microbiología, Universidad Miguel Hernández, Alicante, Spain.
authors.forename: Jose M
authors.initials: JM
authors.lastname: Haro-Moreno
authors.affiliation: Evolutionary Genomics Group, Departamento de Producción Vegetal y Microbiología, Universidad Miguel Hernández, Alicante, Spain.
authors.forename: Francisco
authors.identifier: 0000-0002-9809-2059
authors.initials: F
authors.lastname: Rodriguez-Valera
authors.affiliation: Unité d'Ecologie, Systématique et Evolution, UMR CNRS 8079, Université Paris-Sud, Orsay Cedex, France.
authors.forename: Purificación
authors.initials: P
authors.lastname: López-García
authors.affiliation: Unité d'Ecologie, Systématique et Evolution, UMR CNRS 8079, Université Paris-Sud, Orsay Cedex, France.
authors.forename: David
authors.initials: D
authors.lastname: Moreira
authors.affiliation: Evolutionary Genomics Group, Departamento de Producción Vegetal y Microbiología, Universidad Miguel Hernández, Alicante, Spain.
authors.forename: Ana-Belen
authors.initials: AB
authors.lastname: Martin-Cuadrado
mesh_terms: D019605:Euryarchaeota / Q000145:classification / Q000235:genetics* / Q000302:isolation & purification / Q000378:metabolism; D020745:Genome, Archaeal; D054892:Metagenome; D056186:Metagenomics; D010802:Phylogeny; D012623:Seawater / Q000382:microbiology*