Effect of pH on growth, cell volume, and production of freshwater ciliates, and implications for their distribution

Abstract

We investigated the effect of pH on growth, cell volume, and production of the freshwater ciliates Urotricha farcta, U. furcata, and U. castalia in laboratory cultures with Cryptomonas sp. as food. Overall, pH had a significant, species-specific effect on all parameters investigated. The food alga, Cryptomonas sp., showed a wide pH tolerance, with positive growth rates between pH 4.4 and pH 9.65. Among the ciliates, U. farcta was the most pH-tolerant and U. castalia was the most pH-sensitive species, with positive growth being confined to pH 6.5-8.2. The pH optimum was derived from cellular production rates. The pH optima of the three ciliate species were shifted; their production rates peaked at pH 4.4-5.3 (U. farcta), pH 5.9-7.3 (U. furcata), and pH 6.8-7.9 (U. castalia). The pH effect on growth and survival of the ciliates was minor at circumneutral and moderately alkaline pH values, relative to the effect of temperature and food measured in earlier experiments. The widths of the pH tolerances of the ciliates were positively related to the widths of their temperature niches and to their natural distributions. U. farcta and U. furcata were characterized as euryoecious species, with broad pH and temperature tolerances and ubiquitous distribution; U. castalia is a rare, stenoecious species, requiring specific pH and temperature conditions.

Local adaptation among geographically distant clones of the cosmopolitan freshwater ciliate Meseres corlissi. II. Response to pH

“…The benthic phase, with its characteristic resting cyst (Foissner 2005, Foissner et al 2005, 2006, is an important part of the life cycle of M. corlissi. We extend previous research by investigating the response of M. corlissi to changing pH, another environmental factor that may limit the distribution of ciliates in freshwater (Weisse & Stadler 2006) and soil (Foissner et al 2002).…”

“…Weisse & Stadler's (2006) investigation revealed pH niche separation among 3 species of the common prostome freshwater genus Urotricha. The primary goal of the present study was to assess, for the first time, the extent of intraspecific differences in the pH tolerance of a freshwater ciliate, using Meseres corlissi.…”

“…The effect of pH on the growth and survival of freshwater ciliates has received little attention until recently (Weisse & Stadler 2006). Weisse & Stadler's (2006) investigation revealed pH niche separation among 3 species of the common prostome freshwater genus Urotricha.…”

Effect of lowered pH on marine phytoplankton growth rates

“…Some of these are able to maintain a constant intracellular pH of ~7.0, across an extracellular pH range of 3.0 to 8.0 (Lane & Burris 1981). The freshwater cryptophyte Cryptomonas sp., which is closely related to Rhodomonas marina investigated in the present study, tolerated wide pH fluctuations from pH 4.4 to 9.65 and was able to regulate its cell volume over this range (Weisse & Stadler 2006). Some common freshwater species of the green algal genus Chlamydomonas show positive growth rates over more than 7 pH units and keep their intracellular pH constant over this range (Spijkerman 2005, Gerloff-Elias et al 2006.…”

Biological recovery of the Bohemian Forest lakes from acidification

“…In contrast to many lakes, U. furcata, U. pseudofurcata, and large urotrichas were less abundant as were the genera Holophrya and Prorodon; even Balanion planctonicum occurred in negligible numbers, contrary to its dominance in many oligo-to mesotrophic lakes (e.g., Müller, 1989;Salbrechter & Arndt, 1994;Wille et al, 1999). Little is known about effects of the acid stress on the ciliates so far, but a recent study of the pH effect on three Urotricha species (Weisse & Stadler, 2006) suggests that the current pH in some Bohemian Forest lakes may still be lower than the pH optima of prostomatids.…”