ABSTRACT
In the summer of 1997, Maryland was held captive by a single cell microbe called P esteria piscicida, which was reportedly implicated in killing more than 30,000 1 sh and making ill more than three dozen people in Maryland’s Pocomoke River. In October of that year, a workshop was organized to assess the current knowledge about P esteria, and the critical unanswered questions and necessary research studies to address the crisis. This resulted in a white paper (Greer, J., Lef? er, M., Belas, R., Kramer, J. and Place, A. (1997), In: Zohar, Y., Belas, R., Vasta, G., Place, A., and Kramer, J. (Organizing Committee), Molecular Technologies and P esteria Research: A Scienti1 c Synthesis; https://www.mdsg.umd.edu/MDSG/) that established a set of research priorities. Because of the research performed since then, cultures of P esteria spp. are now available at the Center for Culture of Marine Phytoplankton (CCMP) to all members of the scienti1 c community, as well as molecular probes that distinguish between P esteria spp. and other co-occurring harmful algal blooms (HABS). Further, critical knowledge has been generated that has contributed to a rigorous interpretation of the above mentioned initial environmental and laboratory observations. We now know that physical contact is necessary for P. piscicida to kill 1 sh, and that live 1 sh and/or their products induce excystment and proliferation of P. piscicida. Moreover, the standard tank 1 sh bioassay contains a microbial assemblage that makes it impossible to discern the cause of 1 sh death, even when inoculated with unialgal clones of P esteria. Cultures of P esteria contain a bacterial assemblage that is unique, stable, and needed for optimal growth. Members of the assemblage may also be responsible for the reported toxicity. No evidence for a diffusable toxin being responsible for 1 sh death in nature can be rigorously attributed to P esteria spp. In contrast, a co-occurring dino? agellate, Karlodinium vene cum, that was present in the Pokomoke in 1997, produces water soluble toxins that kill 1 sh through gill disruption. The toxins have been isolated not only from laboratory cultures but also from water samples obtained at the site of 1 sh kills, and their structure has been determined. K. vene cum produces a suite of toxins (karlotoxins, KmTxs), which have not only been shown to possess ichthyotoxicity but are also hemolytic, cytotoxic, and antifungal in nature.
