Biology Faculty Articles


Salt Tolerance of Naked Amoebae

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Journal of Eukaryotic Microbiology







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This study documents the salinity tolerance of naked amoebae from the Salton Sea, California, from intertidal sand in Dania Beach, Florida, and from freshwater. Amoebae were collected from hypersaline ponds around the perimeter of the Salton Sea, where salinities averaged 160‰, and directly from the shoreline waters of the Sea where salinities were generally between 44 and 48‰. Naked amoebae were also collected from the intertidal zone of a Florida beach, a habitat subject to salinity fluctuations in the range 6–85‰. From these sites, six clones of amoebae were isolated for subsequent salinity tolerance experiments (two marine beach isolates, two Salton Sea isolates, and two hypersaline pond isolates). A seventh clone, Acanthamoeba polyphaga, a common freshwater/soil amoeba, was obtained from the Culture Collection of Algae and Protozoa (CCAP), England, UK. The culture experiments compared the effects of gradually changing salinity versus no salinity acclimatization and used growth rate and culture yield as indices of effect. Generally, amoebae were tolerant over a wide range of salinity conditions and were not markedly influenced by pre-conditioning to salinity throughout the experiments. For example, one Salton Sea species, Platyamoeba pseudovannellida n.sp. Hauer, Rogerson & Anderson 2001, was able to survive and grow well without pre-adaptation over the range 0–150‰. Overall, the freshwater amoeba Acanthamoeba grew between 0‰ and 12‰, the marine clones grew in the range of 0–110‰, and the Salton Sea clones reproduced between 0‰ and 150‰. The hypersaline clones were the most resilient and grew between 0‰ and 270‰. The results suggest that most amoebae are essentially unaffected in terms of growth and yield by moderate and severe salinity changes. This might partly explain the high abundances of amoebae found by the authors in salt-challenged environments. Amoebae in the Salton Sea reached 237,120 cells/liter while those in intertidal sand ranged from 181 to 8,473 amoebae/cm3. The survival and activity of large populations of naked amoebae in sites subject to salinity fluctuations suggest that they should be considered in future studies to better understand their, as yet, undefined ecological role

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