The release of oxygen by the roots of wetland plants creates suboxic conditions that may favour the growth of iron-oxidizing bacteria (FeOB). Given their importance in iron cycling, little is known about the diversity or distribution of these bacteria. This is largely due to the lack of efficient methods to study them and the difficulty in isolating them in pure culture. Our study is focussing at the ecology of FeOB by developing molecular and microbiological methods to investigate them in situ. Firstly, gradient tubes were used to enrich and isolate iron-oxidizing bacteria. A novel iron-oxidizing strain related to Gallionella spp. was isolated from an irregularly flooded grassland soil. Secondly, a specific primer set 122f/998r targeting the 16S rRNA gene was developed on the basis of the isolate. The primer set was applied to community DNA obtained from three contrasting wetland environments, followed by DGGE analysis. The PCR products were also used to construct a 16S rRNA gene library. The cloned sequences all represented novel iron oxidizers most closely related to Gallionella spp., and were comparable to the PCR-DGGE result. Thirdly, a SYBR Green qPCR assay was developed. Together with the previously mentioned nested PCR-DGGE method, the qPCR assay was used to quantify the distribution of FeOB in the tidal freshwater marsh. The effects of plant niches, soil depth, elevation gradient and season were investigated. The results showed that the composition of the FeOB community varied with sediment depth, elevation gradient and season, while no influence was observed from plant species. A strong correlation between relative abundance and Fe(III) concentration indicated that the bacterial distribution might be influenced by the iron dynamics. Moreover, oxygen availability and moisture content could serve other steering factors.
|Publication status||Published - 2010|