Diversity of <Emphasis Type="Italic">nifH</Emphasis> gene amplified from plankton-community DNA in a shallow eutrophic lake (Lake Donghu,Wuhan, China)

Biological nitrogen fixation (BNF) is one of the major nitrogen inputs into the biosphere, and the nitrogenase iron protein (nifH) gene plays important roles in regulating the molecular nitrogen (N₂) fixation process. The nifH gene has also been extensively used to study the diversity and function of nitrogen-fixing microorganisms. In this study, we investigated the diversity of the nifH gene by culture-independent methods to analysis the planktonic nitrogen-fixing organisms in Lake Donghu, Wuhan, the largest urban lake in China. Results indicate that nifH gene sequences cloned from planktonic-community DNA showed high similarity to the uncultured cyanobacterial sequences deposited in the GenBank database. Phylogenetic analysis on the basis of the translated amino acid sequences further showed that most nifH clones were closely related to the reported cyanobacterial nifH gene sequences. Results also indicate that there are similar planktonic nitrogen-fixing organisms in the relatively independent areas of Lake Donghu, even though different regions showed a wide gradient in trophic status. These and other observations led us to believe that studies on nifH gene diversity and expression will increase our ability to understand the ecological function of target nitrogen-fixing groups in aquatic ecosystems.