Role of soil in the life cycle of Meseres corlissi (Ciliophora: Oligotrichea): experiments with two clonal strains from the type locality, an astatic meadow pond

Abstract

The life cycle of the oligotrich ciliate Meseres corlissi was investigated using 2 clonal strains, E4 and M10, which were isolated from soil samples collected at the type locality in Salzburg, Austria, and grown in a 1:1 mixture of WC medium and Eau de Volvic on a diet of cryptomonads. Growth, encystment, excystment and cyst survival of both strains depended strongly on the presence or absence of soil components in the culture medium. (1) Growth was enhanced greatly by addition of soil extract or sterilized garden soil. (2) Encystment could be induced by dilution of soil extract concentrations, whereas dilution of ciliates or food algae, at a constant soil extract level, had no significant effect. A sudden decrease in temperature, however, inhibited the encystment reaction. (3) Excystment could be triggered by addition of soil extract or sterilized garden soil. (4) Resting cysts survived desiccation periods of >7 d only in the presence of sterilized garden soil. The nature of the 'soil factor' responsible for these effects remains at present unknown. The growth and encystment responses of strains E4 and M10 differ clearly from those of the earlier investigated strain DR (Weisse 2004), which was isolated from the reservoir of a tree bromelia in the Dominican Republic. These dif- ferences are interpreted as local adaptations of 2 morphologically and genetically indistinguishable but geographically distant populations of a cosmopolitan but rare ciliate species.