J409_25d 507..510
نویسندگان
چکیده
The ocean's interior is Earth's largest biome. Recently, cultivationindependent ribosomal RNA gene surveys have indicated a potential importance for archaea in the subsurface ocean. But quantitative data on the abundance of speci®c microbial groups in the deep sea are lacking. Here we report a year-long study of the abundance of two speci®c archaeal groups (pelagic euryarchaeota and pelagic crenarchaeota) in one of the ocean's largest habitats. Monthly sampling was conducted throughout the water column (surface to 4,750 m) at the Hawai'i Ocean Time-series station. Below the euphotic zone (. 150 m), pelagic crenarchaeota comprised a large fraction of total marine picoplankton, equivalent in cell numbers to bacteria at depths greater than 1,000 m. The fraction of crenarchaeota increased with depth, reaching 39% of total DNA-containing picoplankton detected. The average sum of archaea plus bacteria detected by rRNAtargeted ̄uorescent probes ranged from 63 to 90% of total cell numbers at all depths throughout our survey. The high proportion of cells containing signi®cant amounts of rRNA suggests that most pelagic deep-sea microorganisms are metabolically active. Furthermore, our results suggest that the global oceans harbour approximately 1.3 ́ 10 archaeal cells, and 3.1 ́ 10 bacterial cells. Our data suggest that pelagic crenarchaeota represent one of the ocean's single most abundant cell types. Sampling was carried out at roughly monthly intervals from September 1997 to December 1998 at the Hawai'i Ocean Timeseries station ALOHA (228 459 N, 1588 009 W) in the North Paci®c subtropical gyre. We quanti®ed cells belonging in the domain Bacteria, and two speci®c phylogenetic groups in the domain Archaea, which are prevalent in marine plankton: `group 1 archaea' (referred to here as pelagic crenarchaeota); and `group 2 archaea'
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