Studies on Bacteria Which Produce Paralytic Shellfish Toxins.

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In Ofunato Bay, the shellfish toxicity has been often observed to increase under absence of toxic dinoflagellates. This phenomenon suggests the presence of unknown causative organism (S). Recently, we have found that a bacterium Moraxella sp. isolated from Alexandrium tamarense produces paralytic shellfish toxins (PSP toxins). Thus the link of this bacterium with shellfish toxicity was examined. Analysis of PSP toxins in the particle fractions with different sizes collected from the seawater during the period when the shellfish toxicity increased under absence of toxic dinoflagellate showed that particles with bacterial size possess significant amount of PSP toxins, the profile of which was similar to that of shellfish and dinoflagellate. Moraxella sp. was also detected in the seawater. These findings show the presence of PSP toxins producing bacteria in the ocean that are possibly linked with shellfish toxicity. These also suggest that toxin productivity of the bacteria increases under nutrient poor conditions. Thus Moraxella sp. Was cultured under nutrient poor conditions. Its toxin productivity increased when it was cultured in the natural seawater and left for 10 days, indicating that it produces toxins under starved conditions. PSP toxins producing bacteria were screened in various species of toxic dinoflagellates. Almost all the dinoflagellates gave the intracellular bacteria which showed toxin productivity. These facts support the idea that intracellular bacteria are necessary for the toxin production of dinoflagellates. Bacterial species found in the toxic dinoflagellates were specific to strains as well as species of dinoflagellate, showing the wide distribution of these bacteria. PSP toxins which seemed to originate from bacteria were detected in the bivalves collected from the areas where no dinoflagellates bloom.