Symbiotic relations between bacteria and the domoic acid producing diatom Pseudo-nitzschia multiseries and the capacity of these bacteria for gluconic acid gluconolactone formation

Bacteria isolated from cultures of 4 different strains of the diatom Pseudo-nitzschia multiseries following numerous transfers in a defined medium were identified as mainly Moraxella and Alteromonas sp. These bacteria apparently form a characteristic suite of microorganisms living in a symbiotic relationship with the diatom. The bacterial isolates from each of the P. multiseries strains divided metabolically into 2 groups; those that produced significant amounts of acid from carbohydrates and those that grew readily at the expense of amino acids. The specific acid forming bacteria isolated from each diatom species grown in the presence of glucose produced gluconic acid/gluconolactone in quantity and released it to the surrounding medium. For growth of the diatom a salinity of 33 ppt was more favorable than 26 or 38 ppt; sorbitol varied with the salinity and thus might be an osmolyte. Glucose was present in significant quantities in the diatom grown at all 3 salinities. Nonaxenic growth of the diatom was stimulated considerably by the presence of proline alone and to approximately the same level when it was combined with glucose or sodium acetate, but not when glycine was substituted for the proline. Stimulation of the growth of the diatom by the presence of proline was considered to be a function of the associated bacteria. Glycine combined with sodium acetate was slightly inhibitory to the growth of the diatom but both glycine plus sodium acetate and glycine plus glucose combinations were markedly inhibitory to the growth of the associated bacteria. The possible role of all of these features in the initiation of a bloom of Pseudo-nitzschia multiseries, especially in an inshore environment enriched by organic nitrogen, and the consequent production of domoic acid is discussed.