| Abstract: | Marine bacterial isolates cultured from the digestive tracts of blue mussels (Mytilus edulis) contaminated with paralytic shellfish toxins (PSTs) were screened for the ability to reduce the toxicity of a PST mixture. Seven isolates reduced the overall toxicity of the algal extract by ≥90% within 3 days. These isolates shared at least 99% 16S rRNA gene sequence similarity with five Pseudoalteromonas spp. Phenotypic tests suggested that all are novel strains of Pseudoalteromonas haloplanktis.Among the marine algal biotoxins identified to date; paralytic shellfish toxins (PSTs) constitute the most serious threat to the safety of the food supply, mainly due to their high acute toxicities and the absence of antidotes or effective medical treatments (8). Paralytic shellfish poisoning is caused by ingestion of one or more of the chemically related PSTs (see Fig. S1 in the supplemental material). PSTs are mainly produced by marine dinoflagellates, including Alexandrium spp., Gymnodinium catenatum, and Pyrodinium bahamense var. compresssum (16). Since bivalve molluscs filter-feed on marine algae, they tend to concentrate PSTs largely, but not exclusively, in their digestive organs (7, 9, 10, 29). Not affected by commercial sterilization (14, 18) or cooking, PSTs present significant risks to the food supply, particularly during periods of toxic algal blooms. Practical methods for PST detoxification of living shellfish do not exist (5).Transformations of PSTs by bacteria have been reported in the literature (23-25, 31, 35, 36, 38); early studies focused on the conversion of hydroxysulfate carbamate derivatives (gonyautoxins 1 and 4) to the more highly toxic saxitoxin (STX) (23-25). In addition, several reports have noted the high capacity of the digestive gland for PST transformation (12, 28, 32, 39), suggesting the presence of toxin-transforming enzymes and/or microorganisms in bivalve molluscs. The partial degradation of gonyautoxins 1 and 4 and C1/C2 by marine bacteria has also been reported (38). In addition, Stewart et al. (37) discovered the bacterial degradation of domoic acid (another marine toxin that causes amnesic shellfish poisoning), collectively suggesting that bacteria might play a role in the elimination of marine toxins from toxic bivalve molluscs. The capacity to catabolize domoic acid is greater in cultures isolated from blue mussels that rapidly eliminate domoic acid than in bacterial isolates from bivalves known to retain the toxin for longer time periods (e.g., scallops), suggesting these bacteria play a role in the elimination of marine toxins.Recently, we reported the kinetics of PST destruction for a group of marine bacteria isolated from toxic blue mussels (11). Here we report the phenotypic and taxonomic characterization of these unique marine bacteria. |
