Species- and site-specific bacterial communities associated with four encrusting bryozoans from the North Sea, Germany

Epi- and endozoic bacterial communities associated with four bryozoan species from the Jade (North Sea, Germany) were investigated by the combined application of molecular tools and electron microscopic visualisation of zooids. Denaturing gradient gel electrophoresis of PCR-amplified 16S rRNA gene fragments of associated bacteria displayed specific bacterial community profiles in the examined species Aspidelectra melolontha, Conopeum reticulum, Electra monostachys and Electra pilosa. Actual bacterial epibiosis was only observed on C. reticulum whilst the other bryozoans under investigation were largely free of microbial epibionts. These observations indicated that bryozoan-associated bacteria identified by molecular methods originated from internal cavities of bryozoan zooids. Cluster analysis of DGGE band patterns revealed species-specific bacterial communities in A. melolontha, E. monostachys and E. pilosa. Bacteria associated with C. reticulum were seemingly influenced by site-specific parameters. A comparison of bacterial community profiles between reference and invertebrate surfaces allowed for an interpretation of conspicuous group-specific differences. Operational taxonomic units (OTUs) obtained from a single set of bryozoan replicates that were absent on the inorganic reference samples (mussel shells) were hypothesized to be favourable endobionts. Contrary, OTUs present in the references but absent in bryozoan samples could be assumed to stem from bryozoan-specific defenses against ubiquitous bacterial colonizers. Although there was no experimental evidence for a mutual relationship between prokaryotes and their eukaryotic bryozoan hosts, this study demonstrated that in three out of four bryozoans under investigation associated bacterial communities were characteristically shaped by host attributes.