Monterey Bay cold seep biota: Euglenozoa with chemoautotrophic bacterial epibionts

Deep-sea cold seeps in Monterey Bay, California, are prominent sites of chemosynthetic production, mediated through bacterial oxidation of sulfur. Bacterial mats and vesicomyid clams rely upon hydrogen-sulfide oxidation. Euglenozoa comprise a large and diverse component of the protistan assemblage associated with the dense chemoautotrophic bacterial mats found in the top 1 cm of sediment at some of these seeps. A high percentage of these euglenozoans have conspicuous coats of rod-shaped bacteria that cover virtually their entire surface. In at least one of the three morphotypes identified that possess these epibionts, the epibiotic bacteria contain membrane bound translucent sulfur vesicles. Total sulfide concentration in the top 1 cm of the sediment ranged from undetectable at the sediment-water interface to a maximum of 350 mu M. The presence of other hydrogen sulfide oxidizing bacteria (bacterial mats and endosymbiotic bacteria of the clams), the measurable levels of hydrogen sulfide and the distinct membrane surrounding the sulfur inclusion suggests that the epibiotic bacteria on at least some of the euglenozoans are sulfur oxidizers. This is the first report of flagellates possessing sulfur oxidizing epibiotic bacteria. No evidence has been found that the euglenozoans ingest their epibiotic bacteria, however, and the degree and mode of any nutritional contribution the bacteria might make to the host is unknown.