Ammonia-oxidizing bacteria – Bioindicators for site and seasonal dependent changes in dynamic environments

The community composition of betaproteobacterial ammonia-oxidizers (ß-AOB) in the Elbe Estuary was investigated by sequencing of ammonia monooxygenase subunit A gene (amoA)-amplicons. In the course of the seasons sediment samples from seven sites along the longitudinal profile of the upper Estuary of the Elbe (Hamburg area) were investigated. We observed striking shifts of the ß-AOB community composition according to space and time. Representatives of four Nitrosomonas-lineages and the Nitrosospira-lineage were detected. Members of the Nitrosomonas oligotropha-lineage and the genus Nitrosospira were found to be the dominant AOB within the river transect investigated. Their signatures were detected at all locations during all seasons of the year. However, continuous shifts of balance between members of both lineages along the longitudinal profile were determined. Increased frequencies of sequences affiliated with all other lineages were less pronounced. A noticeable feature was a substantial increase of Nitrosospira-like sequence abundance in autumn and of sequences affiliated with the N. marina-lineage at downstream habitats in spring and summer. Slightly raised relative abundances of sequences affiliated with the N. europaea/N.mobilis-lineage and the N. communis-lineage were found at sampling sites located in the port area. By means of comparisons with environmental parameters we found strong indications that the dynamic of the Elbe Estuary is reflected by shifts in ß-AOB sequence abundance.