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Aquatic Microbial Ecology

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AME 50:135-144 (2008)  -  DOI:

Bacterial involvement in determining domoic acid levels in Pseudo-nitzschia multiseries cultures

James E. Stewart*

Ecosystem Research Division, Department of Fisheries and Oceans, Bedford Institute of Oceanography, PO Box 1006, Dartmouth, Nova Scotia B2Y 4A2, Canada

ABSTRACT: This study examining factors contributing to the production or elimination of domoic acid (DA) in cultures of Pseudo-nitzschia multiseries showed that in axenic cultures doubling the silicate concentrations increased growth, but not DA levels. DA concentration for axenic cultures was increased by the addition of gluconolactone (GlcA), especially in cultures with increased silicon. In non-axenic cultures, there were similar increases in growth with increased silicon, but a reduction of DA production in the presence of GlcA. Detailed examinations confirmed these findings and also showed that in non-axenic cultures, glucose alone resulted in a reduction of DA while a combination of glucose with gluconolactone resulted in a complete elimination of DA. Subsequent trials with axenic P. multiseries cultures showed that additions of DA or DA plus glucose introduced at the early stationary growth phase and incubated for 5 d had no impact on DA concentrations. In contrast, a 6 d incubation of the associated bacteria separated from the non-axenic diatom cultures showed reductions of added DA concentrations ranging from 46 to 72%, depending upon co-additives. The diatom does not use extracellular DA present in surrounding culture medium whereas bacteria associated with the diatom can utilize DA readily. Reductions in the production of DA by aging P. multiseries cultures appear to be the result of changing balances over time among bacteria associated with the diatom. These data coupled with results from other studies indicate that the amount of DA measured in P. multiseries cultures is a result of competitive interaction, i.e. a function of the diatom’s production rate versus the extra-cellular utilization of DA by associated bacteria.

KEY WORDS: Domoic acid · Diatom · Pseudo-nitzschia multiseries · Silicon · Gluconolactone · Glucose

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Cite this article as: Stewart JE (2008) Bacterial involvement in determining domoic acid levels in Pseudo-nitzschia multiseries cultures. Aquat Microb Ecol 50:135-144.

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