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As chloroplast-stealing or "kleptoplastidic" lineages become more reliant on stolen machinery, they also tend to become more specialized on the prey from which they acquire this machinery. For example, the ciliate Mesodinium rubrum obtains > 95% of its carbon from photosynthesis, and specializes on plastids from the Teleaulax clade of cryptophytes. However, M. rubrum is sometimes observed in nature containing plastids from other cryptophyte species. Here, we report on substantial ingestion of the blue-green cryptophyte Hemiselmis pacifica by M. rubrum, leading to organelle retention and transient increases in M. rubrum's growth rate. However, microscopy data suggest that H. pacifica organelles do not experience the same rearrangement and integration as Teleaulax amphioxeia's. We measured M. rubrum's functional response, quantified the magnitude and duration of growth benefits, and estimated kleptoplastid photosynthetic rates. Our results suggest that a lack of discrimination between H. pacifica and the preferred prey T. amphioxeia (perhaps due to similarities in cryptophyte size and swimming behavior) may result in H. pacifica ingestion Thus, while blue-green cryptophytes may represent a negligible prey source in natural environments, they may help M. rubrum survive when Teleaulax are unavailable. Furthermore, these results represent a useful tool for manipulating M. rubrum's cell biology and photophysiology., (© 2024 The Author(s). Journal of Eukaryotic Microbiology published by Wiley Periodicals LLC on behalf of International Society of Protistologists.)

In a previous study, Teleaulax amphioxeia-the preferred prey of Mesodinium in the Columbia River estuary-were undetectable within intense annual blooms, suggesting blooms are prey-limited or prey are acquired outside of bloom patches. We used a novel molecular approach specifically targeting the prey (i.e., Unique Sequence Element [USE] within the ribosomal RNA 28S D2 regions of T. amphioxeia nucleus and nucleomorph) in estuarine water samples acquired autonomously with an Environmental Sample Processor integrated within a monitoring network (ESP-SATURN). This new approach allowed for both more specific detection of the prey and better constraint of sample variability. A positive correlation was observed between abundances of M. cf. major and T. amphioxeia during bloom periods. The correlation was stronger at depth (> 8.2 m) and weak or nonexistent in the surface, suggesting that predator-prey dynamics become uncoupled when stratification is strong. We confirmed exclusive selectivity for T. amphioxeia by M. cf. major and observed the incorporation of the prey nucleus into a 4-nuclei complex, where it remained functionally active. The specific biomarker for T. amphioxeia was also recovered in M. cf. major samples from a Namibian coastal bloom, suggesting that a specific predator-prey relationship might be widespread between M. cf. major and T. amphioxeia., (© 2017 The Author(s) Journal of Eukaryotic Microbiology © 2017 International Society of Protistologists.)

The cryptomonad Rhinomonas nottbecki n. sp., isolated from the Baltic Sea, is described from live and fixed cells studied by light, scanning, and transmission electron microscopy together with sequences of the partial nucleus- and nucleomorph-encoded 18S rRNA genes as well as the nucleus-encoded ITS1, 5.8S, ITS2, and the 5'-end of the 28S rRNA gene regions. The sequence analyses include comparison with 43 strains from the family Pyrenomonadaceae. Rhinomonas nottbecki cells are dorsoventrally flattened, obloid in shape; 10.0-17.2 μm long, 5.5-8.1 μm thick, and 4.4-8.8 μm wide. The inner periplast has roughly hexagonal plates. Rhinomonas nottbecki cells resemble those of Rhinomonas reticulata, but the nucleomorph 18S rRNA gene of R. nottbecki differs by 2% from that of R. reticulata, while the ITS region by 11%. The intraspecific variability in the ITS region of R. nottbecki is 5%. In addition, the predicted ITS2 secondary structures are different in R. nottbecki and R. reticulata. The family Pyrenomonadaceae includes three clades: Clade A, Clade B, and Clade C. All Rhinomonas sequences branched within the Clade C, while the genus Rhodomonas is paraphyletic. The analyses suggest that the genus Storeatula is an alternating morphotype of the genera Rhinomonas and Rhodomonas and that the family Pyrenomonadaceae includes some species that were described multiple times, as well as novel species., (© 2014 The Author(s) Journal of Eukaryotic Microbiology © 2014 International Society of Protistologists.)

We provide here the description of a new marine species that harbors green or red chloroplasts. In contrast to certain other species of the genus, Mesodinium chamaeleon n. sp. can be maintained in culture for short periods only. It captures and ingests flagellates including cryptomonads. The prey is ingested very rapidly into a food vacuole without the cryptomonad flagella being shed and the trichocysts being discharged. The individual food vacuoles subsequently serve as photosynthetic units, each containing the cryptomonad chloroplast, a nucleus, and some mitochondria. The ingested cells are eventually digested. This type of symbiosis differs from other plastid-bearing Mesodinium spp. in retaining ingested cryptomonad cells almost intact. The food strategy of the new species appears to be intermediate between heterotrophic species, such as Mesodinium pulex and Mesodinium pupula, and species with red cryptomonad endosymbionts, such as Mesodinium rubrum., (© 2011 The Author(s) Journal of Eukaryotic Microbiology © 2011 International Society of Protistologists.)