BIODIVERSITY OF GUT MICROFLORA OF Oreochromis niloticus BASED ON CULTURE-INDEPENDENT rRNA GENE ANALYSES AT LAKE NASSER, EGYPT

The diversity of Oreochromis niloticus gut microbiome domains, eukaryotes, bacteria and archaea, was studied to understand the contribution of microbiota to the health of the fish. Fishes were collected from four different Khors, Kalabsha, Wadi Abyad, Tushka and Korosko, of Lake Nasser, Egypt. The approach of this study depends on culture-independent PCR/DGGE and sequence of small subunit of rRNA genes, 18S rRNA gene and 16S rRNA gene. The DGGE patterns displayed 5, 12 and 5 band groups, phylotypes, for eukaryotic 18S rRNA gene, bacterial and archaeal 16S rRNA genes, respectively, in gut contents from the studied khors. DGGE showed bands, which were common and specific for each site and could be used as a bar code to certify the origin of the fish. Statistical analyses, using binary matrix, showed numbers of DGGE bands, 1, 2 and 2, for eukaryotes, bacteria and archaea, respectively, were commonly occurred in all studied khors. The DGGE phylotype, 3.Euk.Kr characterized eukaryotes in Khor Korosko. Phylogenetic analyses showed that two of eukaryotic phylotypes, 1.Euk.Kl.Kr and 2.Euk.Common, were belonged to crustacean Ostracoda. Bacterial phylotypes in all studied khors were located in the branch of cyanobacteria, alpha proteobacteria, but most of them constituted unique phylogenetic lineages within the branch of uncultured environmental bacteria. All archaeal phylotypes were located in the branch of methanogenic uncultured euryarchaeota. Some helminthes, of the genera Neoechinorhynchus and Catenula, -like rRNA gene phylotypes were recorded in guts from Kalabsha, Tushka and Korosko, suggesting common gut parasitic worms. The DGGE patterns and sequence analyses showed high similarities of eukaryote, bacteria and archaea rRNA gene phylotype compositions in fish guts from distant khors, implicating core gut microbiome. This is the first survey of all microbiome domains in tilapia guts at Lake Nasser based on molecular approaches.