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ammonia oxidizing betaproteobacteria; rhizoplane; rhizosphere; 16S rRNA; amoA; Nitrosomonas europaea
Abstract:
Enhanced nitrifi cation and coupled denitrifi cation in macrophyte root zones may contribute to the depletion
of nitrogen from the rhizosphere and are both critical processes for agriculture and rhizoremediation. We
examined one factor likely to affect these processes: the ammonia oxidizing betaproteobacterial community composition,
and whether or not it is infl uenced by plant species (Eleocharis acicularis, Eleocharis palustris, Typha
angustifolia) or sediment characteristics. Genes coding for ammonia monooxygenase (amoA) and 16S rRNA of
betaproteobacterial ammonia oxidizers were targeted. The betaproteobacterial ammonia oxidizing community in
root surface biofi lms was distinct from the surrounding rhizosphere sediment. In contrast, communities in rhizosphere
and bulk sediment samples were very similar. Our results showed the occurrence of Nitrosomonas europaea-
like bacteria nearly exclusively in the rhizoplane biofi lms, while sequences affi liated with the Nitrosomonas
oligotropha, Nitrosomonas communis and Nitrosospira-lineages were more frequently detected in the surrounding
sediment. Our results further suggest that the presence of N. europaea on macrophyte roots depends on the sampling
site rather than on the studied macrophyte species. We propose that the rhizoplane of aquatic macrophytes is
a natural habitat for N. europaea.
