Marine planktonic Archaea take up amino acids

Archaea are traditionally thought of as "extremophiles," but recent studies have shown that marine planktonic Archaea make up a surprisingly Large per centage of ocean midwater microbial communities, up to 60% of the total pro karyotes, However, the basic physiology and contribution of Archaea to comm unity microbial activity remain unknown. We have studied Archaea from 200-m depths of the northwest Mediterranean Sea and the Pacific Ocean near Calif ornia, measuring the archaeal activity under simulated natural conditions ( 8 to 17 degreesC, dark and anaerobic) by means of a method called substrate tracking autoradiography fluorescence in situ hybridization (STARFISH) tha t simultaneously detects specific cell types by 16S rRNA probe binding and activity by microautoradiography. In the 200-m-deep Mediterranean and Pacif ic samples, cells binding the archaeal probes made up about 43 and 14% of t he total countable cells, respectively. Our results showed that the Archaea are active in the uptake of dissolved amino acids from natural concentrati ons (nanomolar) with about 60% of the individuals in the archaeal communiti es showing measurable uptake. Bacteria showed a similar proportion of activ e cells. We concluded that a portion of these Archaea is heterotrophic and also appears to coexist successfully with Bacteria in the same water.