Depth-specific distribution of Bacteroidetes in the oligotrophic eastern Mediterranean Sea

Representatives of the phylum Bacteroidetes are repeatedly reported to be abundant members of oceanic bacterioplankton, probably because of their ability to degrade complex organic matter. 16S rDNA analysis was performed in order to address the importance of this phylum in a highly oligotrophic region such as the Eastern Mediterranean Sea and to investigate its distribution patterns and community composition. A new antisense primer was designed for PCR and used in combination with the general eubacterial sense primer 27F to specifically target Bacteroidetes representatives. Data were correlated with water depth and water mass properties. Denaturant gradient gel electrophoresis (DGGE) analysis and sequencing of environmental clone libraries revealed specific distribution patterns. A major fraction of the sequences was assigned to the AGG58 cluster, a branch of yet uncultured members of the Bacteroidetes lineage. Our results demonstrate a considerable diversity within the Bacteroidetes lineage in the oligotrophic Eastern Mediterranean Sea. Differing water mass properties are considered to be of major relevance for the spatial distribution with depth; several environmental clone sequence clusters could be specifically assigned to a defined water mass or to the deep waters of investigated locations. Depth-specific distribution of Bacteroidetes is demonstrated for the first time by the results of this study.