Bacterial communities in coastal surface waters
along the Egyptian Mediterranean coast
Alaa Eldin A. Bakr
Senior Environmental Researcher, water quality directorate
Egyptian Environmental Affairs Agency, Cairo, Egypt
Jakob Pernthaler
Professor, Limnological Station
Institute of Plant Biology, Zurich University, Switzerland
Jens Harder
Associate Professor, Microbiology Dept.,
Max Planck Institute for Marine Microbiology, Bremen, Germany
Abstract
Bacterioplankton communities from the surface water of the Egyptian Mediterraneancoastal area (between longitudes 27° 15' 45''E and 32° 16' 09''E) are subjected to high amountsof nutrient-rich fresh and brackish water. These communities were examined using 16S rRNAgene clone library, catalyzed reporter deposition fluorescence in situ hybridization (CARD-FISH)and flow cytometry. Twenty eight samples were collected along the study area andchemically analyzed for inorganic nutrients and salinity. Four clone libraries were createdfrom four different sampling points having different concentration of inorganic nutrients. Thecomposition of the four clone libraries was quite different. The main bacterial groupsdominating the clone libraries were Alphaproteobacteria (6-49%), Gammaproteobacteria (26-49%), Cytophaga-Flavobacterium (13-23%) and Cyanobacteria–Chloroplasts (6-28%).Oligotrophic waters were characterized by SAR11, Balenthrix and unculturedgammaproteobacteria; whereas in eutrophic samples Alteromonas, Glaciecola, Colwellia, Marinobacterium and Vibrio were present. The dominant groups were Alteromonas andRoseobacter. The 28 samples were examined by FISH in order to count Roseobacter andAlteromonas-like cells. On average the abundance of Roseobacter was 10%. Alteromonas likecells were less abundant with less than 1% in most of the sampling stations. The abundance ofboth clades was more important in habitats with high nutrient concentration. Flow cytometrywas used also to differentiate the bacterial populations. This analysis was based on the nucleicacid content and the cell size; it showed that total bacterial count, cell size and nucleic acidcontent differed in stations where concentration of inorganic nutrients were different.Eutrophic samples exhibited higher cell number, and larger cell size. These results suggestthat bacterioplankton communities in the Egyptian Mediterranean coastal waters differ bothqualitatively and quantitatively along the Egyptian coast, possibly as a result of the greatvariation in the inorganic nutrient concentration.