The effect of temperature on the toxicity of the laboratory cultured dinoflagellate Ostreopsis lenticularis and its associated bacterial flora.

摘要

Two bacterial strains belonging to the Pseudomonas/Alteromonas and Acinetobacter species were found associated with the dinoflagellate Ostreopsis lenticularis Fukuyo in control cultures. Ostreopsis toxicity and the quantity of recoverable toxic extract were inversely correlated with dinoflagellate growth. The growth of Pseudomonas/Alteromonas was also inversely correlated with Ostreopsis culture growth and directly proportional to the increased dinoflagellate toxicity and quantity of recoverable toxic extract in these cultures. Increased production of dinoflagellate toxic extract specifically increased the growth of the associated Pseudomonas/Alteromonas bacterial strain. Exposure to thermal stress significantly decreased the total Ostreopsis associated bacterial flora. In addition to Pseudomonas/Alteromonas and Acinetobacter, a bacterial strain of the Moraxella species appeared in these cultures. Thermal stress induced the appearance of the Ostreopsis associated Moraxella strain, for when cultures exposed to elevated temperatures were subsequently incubated at normal control temperatures, Moraxella was not among the dinoflagellate associated bacterial flora. The quantities of recoverable toxic extract were inversely correlated with dinoflagellate growth in thermally stressed cultures, as seen in control cultures. Recovered toxic extract quantities significantly increased in these cultures, however, their toxicities were significantly reduced. Thermal stress and the appearance of the Ostreopsis associated bacterial strain Moraxella inhibited the interaction of Ostreopsis and the Pseudomonas/Alteromonas bacterial strain. The growth of this associated bacterial strain was significantly reduced and no longer correlated with dinoflagellate growth or toxic extract production in these cultures. The Pseudomonas/Alteromonas strain was the only Ostreopsis associated bacterial strain that showed significant growth in pure culture when cultivated on dinoflagellate toxic extract at both normal and elevated temperatures. In thermally stressed dinoflagellate cultures the quantities of recoverable toxic extract produced were significantly greater than that seen in the control dinoflagellate cultures because Pseudomonas/Alteromonas did not grow at elevated temperatures in the presence of Ostreopsis cells. The amount of recoverable toxic extract in thermally stressed Ostreopsis cultures increased due to the reduced consumption of toxic extract by the Pseudomonas/Alteromonas bacterial strain. Extract toxicity decreased in these cultures as compared to the control, indicating that in the control cultures Pseudomonas/Alteromonas consumed non-toxic portions of this extract.