12th International Conference on Harmful Algae

INTERNATIONAL SOCIETY FOR THE STUDY OF HARMFUL ALGAE12 th <strong>International</strong> <strong>Conference</strong> on Harmful Algae, Copenhagen, Denmark, 4-8 September 2006at site (2)). The implications of theseresults to the metal dynamics inTâmega River will be discussed.PO. 10-39Effect of carbonateaddition on domoicacid production byPseudo-nitzschiamultiseries in batchcultureSession: PO.10 - Ecophysiology &autecologyBates SS, Léger CSeveral factors control theproduction of the neurotoxindomoic acid (DA) by the diatomPseudo-nitzschia multiseries,including silicate and phosphatelimitation, irradiance level,presence of bacteria, concentrationof copper and iron, and pH. MostDA is produced post-exponentialphase. At that time, theconcentration of CO2 hasdecreased due to photosyntheticuptake, pH is high, and thecarbonate system has shiftedtoward higher proportions ofbicarbonate and carbonate. It istherefore possible that totalinorganic carbon (TIC) may limitDA biosynthesis. To test this,medium f/2 (containing 1.9 mMTIC) was amended with sodiumbicarbonate to give 2.8 and 3.7 mMinorganic carbon. Stationary-phasecell numbers were similar at thethree initial carbon concentrations.TIC decreased during theexponential phase and generallyincreased (unexpectedly) duringstationary phase. pH changed in aninverse fashion, reaching amaximum of 8.95, for the highestTIC concentration, at the end ofexponential growth, and thendeclined during stationary phase.Highest DA was associated withhighest pH.Cellular DA concentrationincreased linearly with increasinginitial TIC concentration (r 2 =0.983), suggesting carbon limitationof DA biosynthesis. Agitation on arotary shaker table increasedgrowth rate and also DAproduction. These conditions maybe used to boost DA production inbatch cultures.PO.06-01Antibiotic synthesis by thebacterium Silicibacter sp. TM1040is involved in the formation ofobligate symbiotic interactionswith dinoflagellatesSession: PO.06 - Population dynamicsM. Robert BelasCenter of Marine Biotechnology,BALTIMORE, United States of AmericaMembers of the Roseobacter cladeof the a-Proteobacteria are amongthe most abundant and ecologicallyrelevant marine bacterial groups.One of the most salient features ofthese bacteria, such as Silicibactersp. TM1040, is their ability tometabolize dinoflagellate-deriveddimethylsulfoniopropionate (DMSP),a major source of organic sulphur inthe ocean. Silicibacter sp. TM1040forms an obligate symbioticrelationship with DMSP-producingdinoflagellates and phytoplanktonsuggesting that the bacteria arehighly adapted to engage in bothpositive and negative interactionswith other marine microorganisms.Silicibacter sp. TM1040 activelymetabolizes DMSP, and ischemotactically attracted todinoflagellate homogenates, DMSP,amino acids, and other chemicalsreleased by the dinoflagellate. Littleis known about the cellular factors132