Composition of Eukaryotic and Prokaryotic rRNA Gene Phylotypes in Guts of Adults and Fingerlings of Mugil cephalus, Inhabiting an Egyptian Mediterranean Estuary

Abstract

To understand the contribution of gut microflora to the feeding and health of Mugil cephalus in a Mediterranean estuary, we have explored and evaluated the diversity of rRNA genes in gut contents of both of adults and fingerlings. Bulk DNAs were extracted from the fish guts, followed by PCR, cloning and sequencing of eukaryote 18S rRNA gene; bacterial and archaeal 16S rRNA genes. Rarefaction analyses recorded 11, 18 and 13 phylotype groups of rRNA genes for eukaryotes, bacteria and archaea, respectively, in the adult guts. The fingerling guts contained 6 and 11 phylotype groups of rRNA genes for eukartyotes and bacteria, respectively, while lacked archaea. Adult and fingerling guts were dominated by zooplankton-like 18S rRNA gene phylotypes, belonging to those of rotifers, genus Brachionus and copepods, genus Apocyclops. Both of diatoms, genus Cyclotella- and fish-like rRNA gene phylotypes were recorded only in adult guts. Phylotypes, which belonged to uncultured proteobacteria and cyanobacteria, covered most of the bacterial 16S rRNA gene composition of adult guts. Bacteroidetes-like phylotypes characterized the fingerling guts. The study showed the first record of uncultured thaumarchaeote-like 16S rRNA genes in the fish guts, opening a window for exploring thaumarchaeote biological significances in fish metabolism. The fish guts represented a reservoir for geographic distant species and reflected the plankton ecosystem variability at the studied estuary. The pollution in the estuary could shape a fraction of the fish gut microbiota. To our knowledge, this work presented the first complete profile of rRNA gene diversities for all known microbiome domains in fish guts.