Population structure and phylogenetic characterization of marine benthic archaea in deep-sea sediments

During the past few years Archaea have been recognized as a widespread and significant component of marine picoplankton assemblages and, more recently , the presence of novel archaeal phylogenetic lineages has been reported in coastal marine benthic environments. We investigated the relative abundanc e, vertical distribution, phylogenetic composition, and spatial variability of Archaea in deep-sea sediments collected from several stations in the At lantic Ocean. Quantitative oligonucleotide hybridization experiments indica ted that the relative abundance of archaeal 16S rRNA in deep-sea sediments (1500 m deep) ranged from about 2.5 to 8% of the total prokaryotic rRNA. Cl one libraries of PCR-amplified archaeal rRNA genes (rDNA) were constructed from 10 depth intervals obtained from sediment cores collected at depths of 1,500, 2,600, and 4,500 m. Phylogenetic analysis of rDNA sequences reveale d the presence of a complex archaeal population structure, whose members co uld be grouped into discrete phylogenetic lineages within the two kingdoms, Crenarchaeota and Euryarchaeota. Comparative denaturing gradient gel elect rophoresis profile analysis of archaeal 16S rDNA V3 fragments revealed a si gnificant depth-related variability in the composition of the archaeal popu lation.