The NifH Gene Diversity in Guanabara Bay Estuarine System
Riva, T.C.; Martins, O.B. and Vieira, R.P.
Instituto de Bioquímica Médica, CCS, UFRJ, Rio de Janeiro, RJ, Brasil.
Nitrogen is one of the fundamental components of biomolecules. It is present in nucleic acids and proteins, being essential to the survival and development of living organisms. In the nature, only a small group of microorganisms, called diazotrophics, reduces atmospheric nitrogen to ammonium. The biological nitrogen fixation is carried out by the protein complex of the nitrogenase. This complex is relativelly conserved in structure and function, and is formed by two metalloproteins: the dinitrogenase reductase (NifH gene) and the dinitrogenase (NifDK gene). The availability of fixed inorganic nitrogen often plays a fundamental role in regulating primary production in both aquatic and terrestrial ecosystems. Because biological nitrogen fixation is an important source of nitrogen in marine environments, the study of N2-fixing microorganisms has fundamental importance to our understanding of global nitrogen and carbon cycles.
To understand the structure of marine diazotrophic communities in a polluted urban bay, the molecular diversity of the nifH gene was studed by PCR using degenerated specific primers, followed by the construction of four nifH gene libraries. Sequences of NifH genes were amplified from environmental DNA samples collected in stations B1 and IL (middle polluted water from inner bay), CM ( high polluted inner channel) and 5K (clean sea water) along a transect from the interior to the exterior of the bay. The free living organisms were separated from the simbiotic and colonial by filtration. The sequences were analysed “in silico” using bioinformatic programs to construct phylogenetic trees with MEGA 3.1 program with the Neighbor-Joining algorithm. We analysed the diazotrophic communities using these trees to compare with that construct from the 16S rDNA phylogenetic marker gene in three stations (B1, CM and 5K). In all libraries were found diazotrophics organisms, many cosmopolitans and a few endemic microorganisms. The most striking data show that the diversity is higher in polluted environments. On the other hand the high concentration of ammonium in that environment put the question of it is due to nitrogenase activity or from industrial and domestic pollution.
Supported by CNPQ AND FAPERJ
|