The abundance of life on Earth is almost entirely due to biological photosynthesis, which depends on light energy. The source of light in natural habitats has heretofore been thought to be the sun, thus restricting photosynthesis to solar photic environments on the surface of the Earth. If photosynthesis could take place in geothermally illuminated environments, it would increase the diversity of photosynthetic habitats both on Earth and on other worlds that have been proposed to possibly harbor life. Green sulfur bacteria are anaerobes that require light for growth by the oxidation of sulfur compounds to reduce CO 2 to organic carbon, and are capable of photosynthetic growth at extremely low light intensities. We describe the isolation and cultivation of a previously unknown green sulfur bacterial species from a deep-sea hydrothermal vent, where the only source of light is geothermal radiation that includes wavelengths absorbed by photosynthetic pigments of this organism.photosynthesis ͉ anoxygenic ͉ green sulfur bacterium ͉ evolution ͉ habitat
On the U.S. west coast, the main toxin-producing algal species are dinoflagellates in the genus Alexandrium that cause paralytic shellfish poisoning (PSP) and diatoms in the genus Pseudo-ni,zschia that produce domoic acid and cause domoic acid poisoning (DAP). Other harmful species, including the raphidophyte Heterosigma uknshiwo and the diatoms Chaetoceros convolutus and Chaetoceros concavicornis, kill fish at aquaculture sites, but arc not harmful to humans. Water discolorations (red tides) caused by nontoxic dinoflagellates also occur throughout the area. Early records, partially based on local native lore, suggest that algal toxins have been present along this coast for hundreds of years, but actual scientific information is sparse. WC review what is now known about harmful algal blooms in this vast area, including the hydrographic regimes that induce and(or) support blooms, bloom dynamics, and the biology of the causative species.
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