Characterization of microbial communities transforming and removing nitrogen in wetlands

The community structure of bacteria responsible for transformation and removal of nitrogen species from farmyard runoff within two different full-scale integrated constructed wetland (ICW) systems was studied. Microbial communities in litter and sediment components were investigated using denaturing gradient gel electrophoresis (DGGE) and band sequencing of the 16S ribosomal ribonucleic acid gene fragments of putative ammoniaoxidizing bacteria and the nitrite reductase genes (nirK/S) of putative denitrifying bacteria. Findings show that retrieved sequences of ammonia-oxidizing bacteria communities in litter samples were related to Nitrosomonas and Nitrosospira, while those from sediment samples were related to only Nitrosospira. A more diverse denitrifying community was present in the litter compared to the sediment samples. Non-metric multi-dimensional scaling analysis showed that microbial communities were readily distinguishable with respect to site and source (sediment and litter) for the two representative example ICW systems. A comparison of the species composition of the ammoniaoxidizing bacteria and denitrifiers in the systems revealed that the communities were no more similar or dissimilar than if they had been assembled by chance.