Comparative analysis of ammonia-oxidizing bacterial communities in two lakes in North Germany and the Baltic Sea

One important pathway of the nitrogen cycle in aquatic environments is the oxidation of ammonia to nitrite by ammonia-oxidizing bacteria (AOB). In this study the composition of AOB communities was compared between fresh (lakes Plusssee and Schöhsee) and brackish (Baltic Sea) water at two different levels: i) between environments and ii) within different depths in each environment. Changes in the community structure were studied by denaturing gradient gel electrophoresis (DGGE) and clone libraries of PCR products of 16S rRNA genes (rDNA) from AOB of the beta subclass of proteobacteria. Each environment displayed a particular DGGE band pattern. In Plusssee and the Baltic Sea, the differentiation of communities in epi- and metalimnion from those in hypolimnion coincided with a distinct stratification of the water column. In Schöhsee with an aerobic hypolimnion, the communities at all depths were similar. AOB communities in sediments were different from those in the water column. The composition of clone libraries showed the presence of specific Nitrosomonas and Nitrosospira-like sequences in each environment and habitat.