VERTICAL-DISTRIBUTION AND PHYLOGENETIC CHARACTERIZATION OF MARINE PLANKTONIC ARCHAEA IN THE SANTA-BARBARA CHANNEL

Newly described phylogenetic lineages within the domain Archaea have r ecently been found to be significant components of marine picoplankton assemblages. To better understand the ecology of these microorganisms , we investigated the relative abundance, distribution, and phylogenet ic composition of Archaea in the Santa Barbara Channel. Significant am ounts of archaeal rRNA and rDNA (genes coding for rRNA) were detected in all samples analyzed. The relative abundance of archaeal rRNA as me asured by quantitative oligonucleotide hybridization experiments was l ow in surface waters put reached higher values (20 to 30% of prokaryot ic rRNA) at depths below 100 m. Probes were developed for the two majo r groups of marine Archaea detected. rRNA originating from the euryarc haeal group (group II) was most abundant in surface waters, whereas rR NA from the crenarchaeal group (group I) dominated at depth. Clone lib raries of PCR-amplified archaeal rRNA genes were constructed with samp les from 0 and 200 m deep. Screening of libraries by hybridization wit h specific oligonucleotide probes, as well as subsequent sequencing of the cloned genes, indicated that virtually all archaeal rDNA clones r ecovered belonged to one of the two groups. The recovery of cloned rDN A sequence types in depth profiles exhibited the same trends as were o bserved in quantitative rRNA hybridization experiments. One representa tive of each of 18 distinct restriction fragment length polymorphism t ypes was partially sequenced. Recovered sequences spanned most of the previously reported phylogenetic diversity detected in planktonic cren archaeal and euryarchaeal groups, Several rDNA sequences appeared to b e harbored in archaeal types which are widely distributed in marine co astal waters. In total, data suggest that marine planktonic crenarchae a and euryarchaea of temperate coastal habitats thrive in different zo nes of the water column. The relative rRNA abundance of the crenarchae al group suggests that its members constitute a significant fraction o f the prokaryotic biomass in subsurface coastal waters.