Relative nutritional value of ciliate protozoa and algae as food forDaphnia

Taxonomy and SSU rRNA gene-based phylogeny of two new Euplotes species from China: E. chongmingensis n. sp. and E. paramieti n. sp. (Protista, Ciliophora)

Background

The genus Euplotes Ehrenberg, 1830, one of the most complicated and confused taxa, contains about 160 nominal species. It was once proposed to be divided into four genera, two of which were proved to be non-monophyletic. At least 19 new species have been discovered in the past decade, implying that there is a large undiscovered diversity of this genus.

Results

The morphology of two new freshwater euplotid ciliates, Euplotes chongmingensis n. sp. and E. paramieti n. sp., isolated from Shanghai, China, were investigated using live observations, protargol staining, and Chatton-Lwoff silver staining method. Euplotes chongmingensis is characterized by its small size (40–50 × 25–35 μm), about 24 adoral membranelles, 10 frontoventral cirri, two marginal and two caudal cirri, eight dorsolateral kineties with 11–16 dikinetids in the mid-dorsolateral kinety and a double type of silverline system. Euplotes paramieti n. sp. is 180–220 × 110–155 μm in vivo and strongly resembles E. amieti but having a difference of 57 bp in their SSU rRNA gene sequences. Phylogenetic analyses based on SSU rRNA gene sequence data were used to determine the systematic positions of these new taxa.

Conclusions

The description of two new freshwater taxa and their SSU rRNA gene sequences improve knowledge of biodiversity and enrich the database of euplotids. Furthermore, it offers a reliable reference for environmental monitoring and resource investigations.

“In vitro” evaluation of the bacterivore potential of three Cladoceran species occurring in tropical and subtropical regions

Abstract Cladocerans occupy an important position among the bacterial consumers in freshwater food webs, being relatively non-selective filter feeders that can exert a strong impact on microbial populations. We evaluated the bacterivory potential of three cladocerans species of subtropical and tropical occurrence (Ceriodaphnia silvestrii, Daphnia gessneri and Ceriodaphnia cornuta) at different life stages, by scanning electron microscopy (SEM) and by the quantification of their bacterial consumption rates using fluorescently labeled bacteria (FLB). All species showed filter mesh sizes sufficiently narrow to retain bacteria. The largest distance between setules was found in primiparous C. cornuta, and the smallest in neonate D. gessneri. The lowest ingestion (IR) and removal (RR) rates were observed in primiparous C. silvestrii and the highest values were observed in adults of D. gessneri. We conclude that bacteria may be considered an important food supplement, particularly for neonates who presented smaller intersetular distances and higher filtration rates than the other life stages.

Sterol composition of freshwater algivorous ciliates does not resemble dietary composition

Algivorous ciliates represent an important link in freshwater food webs, as they transfer energy and biochemical matter from their algal prey to mesozooplankton predators. However, it is still unknown how dietary composition influences the biochemical composition of ciliates. We analyzed the sterol composition of the algivorous ciliates Balanion planctonicum and Urotricha farcta and compared it to the sterol composition of their diet--the cryptomonad Cryptomonas phaseolus. The sterol composition of the ciliates did not resemble that of their algal diet. Ergosterol [(22E)-ergosta-5,7,22-trien-3beta-ol] was the sterol in highest concentration in C. phaseolus, whereas stigmasterol [(24S)-24-ethylcholesta-5,22E-dien-3beta-ol] was dominant in both B. planctonicum and U. farcta. Moreover, the occasionally higher sterol concentrations in the ciliates than in their algal diet suggest sterol accumulation by the ciliates. We conclude that dietary sterol composition influences the composition of the two algivorous ciliates studied, but species-specific differences in metabolism probably determine the ultimate sterol composition of the ciliates.

Supplementation with Sterols Improves Food Quality of a Ciliate for Daphnia magna

Experimental results provide evidence that trophic interactions between ciliates and Daphnia are constrained by the comparatively low food quality of ciliates. The dietary sterol content is a crucial factor in determining food quality for Daphnia. Ciliates, however, presumably do not synthesize sterols de novo. We hypothesized that ciliates are nutritionally inadequate because of their lack of sterols and tested this hypothesis in growth experiments with Daphnia magna and the ciliate Colpidium campylum. The lipid content of the ciliate was altered by allowing them to feed on fluorescently labeled albumin beads supplemented with different sterols. Ciliates that preyed upon a sterol-free diet (bacteria) did not contain any sterols, and growth of D. magna on these ciliates was poor. Supplementation of the ciliates' food source with different sterols led to the incorporation of the supplemented sterols into the ciliates' cells and to enhanced somatic growth of D. magna. Sterol limitation was thereby identified as the major constraint of ciliate food quality for Daphnia. Furthermore, by supplementation of sterols unsuitable for supporting Daphnia growth, we provide evidence that ciliates as intermediary grazers biochemically upgrade unsuitable dietary sterols to sterols appropriate to meet the physiological demands of Daphnia.

Biochemical composition of algivorous freshwater ciliates: you are not what you eat

The focus of our study was to determine whether the biochemical composition of two algivorous ciliates, both fed the same alga, resembles that of their diet. By comparing both ciliated protozoa we intended to identify species-specific differences in the metabolic features of these ciliates. Carbon- and cell-specific concentrations of fatty acids and essential amino acids were investigated for the ciliates Balanion planctonicum and Urotricha farcta grown on the cryptomonad Cryptomonas phaseolus. Stepwise discriminant analyses (SDA) indicated differences in the biochemical composition between ciliates and their diet and between the two ciliated protozoa. Carbon-specific fatty acid concentrations were usually higher in the ciliates than in their diet, especially concentrations of monounsaturated and some polyunsaturated fatty acids. Except for tryptophan, valine, and lysine, amino acid concentrations were higher in the ciliates than in C. phaseolus. Furthermore, differences in the polyunsaturated fatty acids accounted for the largest discrepancies between the two ciliated protozoa. The higher concentrations in the ciliates compared to their diet suggest that these species are capable of efficiently ingesting, assimilating or possibly synthesizing some fatty acids and amino acids. We conclude that dietary fatty acid and amino acid composition influences the composition of the two ciliated protozoa to a minor extent, and that species-specific differences in fatty acid and amino acid metabolism may be more important determinants of the biochemical composition of the studied ciliates. Moreover, the metabolism of polyunsaturated fatty acids seems to differ more profoundly between the two ciliated protozoa than the metabolism of other fatty acid classes or amino acids.