Structure of the Archaeal Community in the Black Sea Photic Zone

Qualitative and quantitative analysis of the structure of the archaeal community of the photic zone of the Black Sea water column was carried out. Real-time PCR revealed 2 × 104 archaeal cells/mL (4.2% of the total cell number) at a 15-m depth. The structure of archaeal communities in the subsurface water column was investigated using the sequencing by synthesis technology (Illumina/Solexa) of the 16S rRNA genes. The Marine Group II phylogenetic cluster belonging to the phylum Euryarchaeota was the most numerous archaeal group (1.2–1.7 × 104 cells/mL). The Marine Group I phylogenetic cluster (phylum Thaumarchaeota) was the second most numerous group (40% of the free-living archaea or 7.7 × 103 cells/mL). Sequences of the ‘Nitrosopumilus’ cluster were revealed among Marine Group I sequences due to high homology (over 90%). A group of archaea belonging to the Deep-sea Hydrothermal Vent Euryarchaeotic Group 6 (DHVEG-6) (phylum Euryarchaeota) was also detected. The 16S rRNA gene sequences belonging to this cluster were revealed only in the suspension fraction. High homology level (over 90%) suggested classification of most DHVEG-6 sequences within the ‘Parvarchaeum’ cluster. In spite of a noticeable methane peak detected at 15-m depth, no sequences of methanogens were found.