Tolerance of flagellated protists to high sulfide and metal concentrations potentially encountered at deep-sea hydrothermal vents

The survival rates of 3 species of deep-sea hydrothermal vent flagellates were measured after exposure to chemical conditions potentially encountered in vent environments. The survival rates, measured as viability through time, of Caecitellus parvulus, Cafeteria sp. and Rhynchomonas nasuta were determined and compared to shallow-water strains of the same species after exposure to increasing concentrations of sulfide or the metals Cu, Fe, Mn and Zn. Responses were variable but in all cases these flagellates showed very high tolerance to extreme conditions. Cafeteria spp. were remarkable in that both strains showed 100 viability after a 24 h exposure to 30 mM sulfide under anoxic conditions, By contrast, the highest naturally occurring sulfide concentrations ever measured are only 18 to 20 mM, There was little effect from metals at concentrations up to 10(-3) M total metal, but a sharp decrease in viability occurred between 10(-3) and 10(-2) M total metal, due either to a rapid increase in the availability of free metal ions or colloid formation or both, This study is consistent with other previously reported studies that indicate these flagellate species are present and capable of being active members of the microbial food webs at deep-sea vents.