Stability of bacterial and viral community compositions in Danish coastal waters as depicted by DNA fingerprinting techniques

Variations in bacterial and viral community compositions were examined over spatial scales ranging from centimeters to kilometers and over temporal scales of days to months in Danish coastal environments by means of denaturing gradient gel electrophoresis (DGGE) and pulsed field gel electrophoresis (PFGE), respectively. Despite several-fold differences in bacterial activity and chlorophyll a, we found only a few differences in microbial community composition among samples from 30 cm intervals in a 3 m vertical profile across a narrow pycnocline during a subsurface coccolithophorid bloom in the southern Kattegat. Likewise, only a few changes in community composition were observed during a 2 mo spring bloom period in the eutrophic Roskilde Fjord. However, more pronounced differences were observed among samples from 5 stations on a transect crossing the Skagerrak-Kattegat front where 2 water masses with different physico-chemical properties meet. The 2 water masses harbored distinct bacterial and viral communities, and a gradual mixing of the microbial communities was observed across the front. Our study indicates stability of microbial community compositions in Danish coastal waters and suggests that changes in microbial abundance and activity were not associated with successions in bacterial and viral communities discernible by the applied DGGE and PFGE protocols.