Phylogenetic Diversity Of Nitrogen Fixation Bacteria And NifH Gene Associated With The Rhizosphere Soil Of Mangrove Trees

Twelve aerobic free living nitrogen-fixing bacteria were isolated from nine rhizosphere soil samples of mangrove trees. Twelve 16S rDNA and nine nifH sequences of isolates were obtained by PCR, respectively. Two kinds of phylogenetic trees were constructed basing on 16S rDNA and nifH sequences of the isolates and available in GenBank. Comparison of two phylognetic trees, it was found that the aligment is similar only for a few strains, providing evidence that the difference in rates of evolution between 16S rRNA and nifH gene. By using PCR-Clone-Sequencing, a culture-independent approach, twenty-seven nifH sequences were obtained from three rhizosphere soil samples of mangrove trees. Neighbor-joining phylogenetic tree of nifH was constructed basing on all nifH sequences from mangrove ecosystem in GenBank as well as nifH sequences obtained in this study. It demonstrated that nifH diversity varied among different soil samples within a mangrove ecosystem, especially among samples with distinct physico-chemical properties; while among different geographical mangrove ecosystem, this is the first report, that the nifH sequences obtained from the same area were inclined to cluster as an independent group.The results implied that the composition of diazotrophs community in mangrove soil is mainly dependent on the specific characteristics of enviromental sample, but poorly associated among geographically isolated mangrove ecosystem.