Bacteria-Phytoplankton Interactions: The Influence of Marine Bacteria on Alexandrium spp. Blooms in the Gulf of Maine

University Of Massachusetts Lowell Research Foundation, Lowell MA

Investigators

Abstract

Blooms of the toxic dinoflagellates of the genus Alexandrium have become a chronic problem affecting large areas of the Gulf of Maine (GOM) on a near-annual basis. These algae are the causative agents of paralytic shellfish poisoning, a potentially fatal neurological disorder. Concerns for public health have resulted in frequent shellfish quarantines, permanent closure of some shellfish beds, and the implementation of costly PSP toxin monitoring programs in the GOM. Although considerable effort has been made to determine the environmental factors that influence Alexandrium spp. population dynamics in the GOM, the factors that control in situ growth and decline of Alexandrium populations remain poorly understood. Interactions between the marine bacteria and toxic phytoplankton are thought to play a major role in controlling toxic algal blooms, but their potentially important role in the GOM has received little attention. It is well known that bacteria and phytoplankton dynamics are tightly linked in coastal marine environments, with strong associations frequently observed between bacterial and phytoplankton biomass. In addition, both positive and negative influences of bacteria on specific harmful algal bloom (HAB) organisms have been documented. Initial research results have indicated GOM bacteria capable of dramatically stimulating Alexandrium under laboratory conditions and that these interactions may vary seasonally. This project will elucidate the role of bacteria in Alexandrium spp. population dynamics in the GOM. Several aspects of bacteria-Alexandrium interactions will be investigated, including: the seasonal and spatial distribution of bacteria that inhibit or promote Alexandrium growth; the specificity of bacteria-Alexandrium interactions; and the biotic and abiotic factors that influence bacterial community dynamics. Field research will be conducted in the southwestern Bay of Fundy with Canadian collaborators. In addition, archived bacterial community samples that were collected from the eastern and southwestern GOM in collaboration with the ECOHAB-GOM sampling program in 1998 and 2000 will be analyzed to determine the geographic distribution of specific bacteria found to interact with Alexandrium. Close collaboration with the ECOHAB-GOM team and the DFO HAB program will provide an extensive array of data and access to research vessels. Experimental methods to analyze bacteria-Alexandrium interactions will include: (1) molecular phylogenetic (PCR-DGGE and MPN-PCR) and cultivation-based analysis of the seasonal and geographic distribution of bacterial assemblages that inhibit or promote Alexandrium; (2) enrichment and isolation of novel bacterial strains that interact closely with Alexandrium; (3) analysis of the influence of Alexandrium- promoting or Alexandrium-inhibiting bacteria on other algal species present in the GOM; and (4) analysis of the isolates' influence on Alexandrium growth in mixed cultures. The study will provide insight into interactions between Alexandrium and bacteria in the GOM and may ultimately improve our ability to simulate and predict Alexandrium dynamics within a given body of water. This research will determine whether certain bacterial assemblages are associated with Alexandrium spp. in the GOM and will also explore Alexandrium -bacteria interactions that may promote or inhibit Alexandrium growth.