Gluconic acid/gluconolactone: physiological influences on domoic acid production by bacteria associated with Pseudo-nitzschia multiseries

A single strain of Pseudo-nitzschia multiseries was grown axenically and in parallel cultures to which selected bacterial species isolated previously from P. multiseries cultures were added (non-axenic culture), an Alteromonas sp. (a producer of gluconic acid/gluconolactone when grown with glucose) and a Moraxella sp. (a non-producer of gluconic acid/gluconolactone). When gluconic acid/gluconolactone was added to the axenic culture the production of domoic acid was increased to double that produced by the non-axenic culture. The effect of the gluconic acid/gluconolactone on domoic acid production was concentration dependent and could be offset completely by the addition of glutamic acid or proline to cultures containing gluconic acid/gluconolactone. Domoic acid, depending upon culture conditions, was partitioned in varying percentages between the diatom cells and the culture filtrates. It is suggested that the enhancement of the algal production of domoic acid in the presence of specific bacteria could be influenced by production of gluconic acid/gluconolactone by bacteria; this effect may be a direct result of the antagonistic effect of the powerful sequestering properties of gluconic acid which, through tying up nutrients, induces the diatom to produce a counter chelating agent, domoic acid.