No abstract

Nile tilapia, Oreochromis niloticus is widely distributed in Africa and many parts of the world (Trewavas, 1983). It was introduced into Lake Victoria, the main Nile source, in the 1950s together with other tilapiines like O. leucostictus (Graham), Tilapia zillii (Gervais) and T. rendalii (Boulenger) (Trewavas, 1983). The Tilapias are living mainly at khors of Lake Nasser, as favorite habitats due to high eutrophication (El-Shabrawy and Dumont, 2003). The dominance of O. niloticus over other tilapiines in the Lake Nasser is attributed to several factors including high fecundity and fast growth rates (Welcomme, 1967; Balirwa, 1998).

Bacterial populations within hypersaline lakes often exhibit uncultured unique species. Polymerase chain reaction-denaturing gradient gel electrophoresis (PCR-DGGE), followed by sequencing of 16S rRNA gene approach was applied in order to explore, for the first time, the bacterial communities within the hypersaline Lakes, Aghormy, Zeiton and Maraqi, Siwa Oasis, Egypt. The DGGE profile displayed 12 phylotypes of 16S rRNA gene, representing the total species richness within the three studied lakes. The phylotypes were varied among lakes, but were restricted to two phylogenetic groups, Bacteroidetes, which occurred in all lakes, and Alphaproteobacetria, which showed abundance in only Lakes Zeiton and Maraqi. Single spirochete-like phylotype characterized the Lake Aghormy. A phylotype, which was recorded in both of Aghormy and Zeiton, represented a first recorded of Lewinella agarilytica in hypersaline inland lakes. Sequence homology results suggested novel indigenous bacterial phylotypes.