| Paralytic shellfish toxins PSTs are the agents of paralytic shellfish poisoning (PSP), a potentially fatal foodborne illness linked to the consumption of PST-contaminated shellfish in coastal waters worldwide. Although toxic dinoflagellates are generally regarded as the primary source of PSTs, bacteria have also been found capable of autonomous production. Discrepancies in toxin profiles between producing organisms and contaminated bivalves have been widely recorded. Based on these observations, there has been much speculation as to the mechanisms involved in PST biotransformations in shellfish and their tissues. Similar transformations have also been investigated in bacteria isolated from PST-contaminated bivalves. The purpose of the current study was to isolate bacteria from toxic blue mussels (Mytilus edulis) and soft-shell clams (Mya arenaria) harvested in Atlantic Canada and screen them for the ability to reduce the toxicity of a PST mixture. Those isolates demonstrating PST degradation were characterized and identified.;The isolates were grown in a supplemented media with a toxic algal extract (AE) and screened for the presumptive degradation of PSTs using liquid chromatography (LC). Reduction of overall toxicity was verified by mouse bioassay (MBA) in which four isolates demonstrated the most complete PST degradation. During the screening process, the four cultures split into opaque and translucent colony phenotypes and, henceforth, were treated as eight separate isolates. The eight isolates reduced the overall toxicity of the AE ≥ 90 % within 3 d of incubation. In all cases, the overall degradation kinetics of the PSTs were first order, as were the individual kinetics of toxins STX, NEO, GTX 2, C1, and C2. The degradation curves of toxins GTX 3, dcGTX 3, and dcGTX 2 were fitted to cubic functions. All isolates degraded 100 % of the NEO in the AE within 2 d, and most degraded 100 % of the STX within 1--3 d. Since all of the competent isolates are obligate aerobes, degradation of the PSTs was likely catalyzed by oxidative enzymes. Based on 16S rDNA sequences, the isolates were all placed in the genus Pseudoalteromonas. Further phenotypic testing suggested that the isolates are all strains of P. haloplanktis. |
