Phylogenetic diversity of bacteria associated with Alexandrium spp. and other phytoplankton from the Gulf of Maine

Measurement of bulk community parameters indicates a close link between bacteria and phytoplankton dynamics in marine environments but little is known about how these communities interact at species-composition level. The objective of this study was to determine whether there are specific interactions between diverse phytoplankton and bacteria that are closely associated with them. Our analysis included major taxonomic groups of phytoplankton in the Gulf of Maine (GOM), including Alexandrium spp., from the GOM and elsewhere. DNA was extracted and amplified with a primer set that targets most Bacteria. The PCR products were analyzed using denaturing gradient gel electrophoresis (DGGE). DGGE bands were recovered from the gel, and either sequenced directly or cloned into E. coli and then sequenced.; In particular, Rhodobacter and Cytophaga-Flavobacterium-Bacteroides groups were important members of assemblages in most phytoplankton cultures. The results indicate that specific bacteria-phytoplankton interactions may exist, but they are not the result of coevolutionary relationships that might occur in tight symbioses.