Microbial utilization of the neurotoxin domoic acid: blue mussels (Mytilus edulis) and soft shell clams (Mya arenaria) as sources of the microorganisms

Abstract

The neurotoxin domoic acid is produced in quantity by the diatom Pseudo-nitzschia multiseries and is released to the environment directly and indirectly via food chains. Presumably there is a mechanism for the biodegradation and disposal of domoic acid and as bacteria are logical candidates for such an activity, a search for bacteria competent to carry out biodegradation of domoic acid was initiated. Extensive trials with a wide variety of bacteria isolated mainly from muds and waters taken from the marine environment showed that the ability to grow on or degrade domoic acid was rare; in fact, domoic acid was inhibitory to resting cells or growing cultures of most of these bacteria. In contrast, using enrichment techniques, it was possible to isolate from molluscan species that eliminate domoic acid readily, i.e., blue mussels (Mytilus edulis) and soft-shell clams (Mya arenaria), bacteria that exhibited growth with and biodegradation of domoic acid when supplemented with low concentrations of growth factors. The species that retain domoic acid for lengthy periods, such as sea scallops (Placopecten magellanicus) and red mussels (Modiolus modiolus), only occasionally yielded bacteria with this capability. The differences may be a result of the mechanisms used by the different shellfish in dealing with domoic acid, i.e., freely available in the blue mussels and soft-shell clams but likely sequestered in the digestive glands of sea scallops and red mussels and thus, largely unavailable for bacterial utilization. The results show that Mytilus edulis and Mya arenaria, almost uniquely, are prime and reliable sources of domoic acid utilizing bacteria. These findings suggest a strong possibility that autochthonous bacteria may be significant factors in the elimination of the neurotoxin in these two species of shellfish.

Bacterial community composition differs with species and toxigenicity of the diatom Pseudo-nitzschia

“…Kaczmarska et al (2005) hypothesized that Pseudo-nitzschia produces higher levels of DA as a chemical defense against greater numbers or diversity of bacteria. Alternatively, we suggest that, if DA inhibits the growth of some bacteria (Stewart et al 1998), bacterial richness in toxigenic cultures may instead be lessened (as seen here) due to the inhibitory effects of DA. We hypothesize that, over a time frame of months in culture, toxigenic strains of Pseudonitzschia cycled between high-DA conditions during the stationary phase and low-DA conditions following each transfer, eventually favored a bacterial community able to persist under both conditions (DA-utilizing and DA-tolerant bacteria).…”

“…Along these lines, there is some evidence that some bacterial strains may utilize DA. Specifically, the growth of some bacteria on a complex medium is enhanced by the presence of DA, while the growth of other strains may be inhibited by it, as evidenced by the creation of clear zones on bacterial lawns (Stewart et al 1998). In the field, bacteria from regions of Pseudo-nitzschia blooms have been shown to degrade DA more quickly than bacteria from other regions (Hagström et al 2007).…”

Domoic acid uptake and elimination kinetics in oysters and mussels in relation to body size and anatomical distribution of toxin

“…periodic and non-synchronous shell closure) (Bougrier et al, 2003;Baron et al, 2006). It may also be related to genetic differences such as differential enzymatic activity, or differential prevalence of bacterial strains capable of DA degradation in the bivalve gut flora (Stewart et al, 1998;Hagström et al, 2007).…”

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

“…DA is utilized by bacteria isolated from shellfish (blue mussels and soft shell clams, Mya arenaria) and by bacterial strains isolated from Pseudo-nitzschia multiseries cultures [strains N-7, a Moraxella species and N-9, an Alteromonas species ] (Stewart et al 1998). All of these bacteria supplied with low concentrations of growth factors readily cause the disappearance of DA presented in moderate concentrations of 40 or 80 nM.…”