Experimental bleaching of photosymbiotic amoeba revealed strain-dependent differences in algal symbiosis ability
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Abstract
Photosymbioses, the symbiotic relationships between photosynthetic algal symbionts and non-photosynthetic eukaryotic hosts, are sporadically found in a lot of eukaryotic lineages, but only a few taxa, such as cnidarians and ciliates hosting algal endosymbionts, have been actively studied for a long time. That has hindered understanding the universal mechanisms of the photosymbiosis establishment. Especially in Amoebozoa, only two species, Mayorella viridis and Parachaos zoochlorella , are reported as photosymbiotic in nature, and their mechanisms of establishing symbiotic relationships are still unclear. To investigate the extent to which and how photosymbiotic amoebae depend on the symbiotic relationships, M. viridis were treated with reagents that are known to induce the collapsing of photosymbiotic relationships, or bleaching, in other photosymbiotic species. As a result, we succeeded in artificially removing algal symbionts from host M. viridis cells with an herbicide, 2-amino-3-chloro-1,4-naphthoquinone. The apo-symbiotic state amoeba cells were able to survive and grow to the same extent as the symbiotic state cells when they fed microbial prey, indicating that the algal symbionts are not essential for the host growth under certain conditions. Furthermore, to see whether the photosymbiotic state is reversible, we fed two strains of algal symbionts to the apo-symbiotic amoeba host. The result showed that the apo-symbiotic hosts were able to ingest symbiont cells and re-establish the symbiotic state. The efficiencies of ingesting algal cells were significantly different depending on algal symbiont strains, indicating that different algal strains possess discrete symbiotic abilities to M. viridis . To our knowledge, we provide first insights on the establishment and collapse of photosymbiosis in Amoebozoa, which pave the way to understand the universal mechanism of photosymbiosis utilizing M. viridis as a model system.
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Conclusion
Thank you for sharing this really interesting paper! The bleaching methods will surely contribute to a lot of future work! Super cool system!!!
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han A (Fig. 1 D).
Were there any benefits to the host M. viridis that you observed by having 1 strain of Chlorella instead of the other?
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Quantification of symbiotic abilities of algae to M. viridis
Were you able to notice any differences in the appearance of Chlorella strains that were symbionts vs free-living? A recent pre-print showed extensive morphological changes to Chlorella species when they were established as endosymbionts of Paramecium bursaria (https://www.biorxiv.org/content/10.1101/2023.12.22.572971v1)
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We found that the number of Chlorella cells ingested by M. viridis was significantly higher in strains B than A (Fig. 1 D).
If I read correctly, these measurements were taken after 1 hour co-incubation, correct? Were the re-established symbionts present after longer time periods? Is it possible these were ingested as a food source and weren't fully digested yet?
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Two Chlorella strains (strain A and B) were isolated from M. viridis culture and grown in 20 mL
Were these free-living in the culture medium? or did you need to rupture the host cell to isolate these?
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In addition, the symbiotic abilities of two Chlorella strains are different, though these strains were isolated from the original M. viridis culture.
Interesting! Have y'all tried trying to re-establish the symbiosis with a co-culture of Strain A & Strain B? I'm just wondering if there could be a synergistic benefit of both strains (since strain A was naturally able to compete its way into the host). Further, do you think that a non-Chlorella species of microalgae could become an endosymbiont? I'm wondering if the non-photosynthetic microalgae C. paramecium that you feed them could be a symbiont that isn't recognized because its not easily visible in the cell?
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On the other hand, no chlorophyll fluorescence was observed in M. viridis cells treated with ACN for one week (Fig. 1 A).
Is the ACN actually killing the endosymbiont? or does it cause them to be flushed from the host?
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Cryptomonas paramecium (NIES-715) was used as feed for M. viridis.
Are the symbiotic-state cells able to survive without this external food (using Chlorella photosystems for energy)?
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Although eukaryotic species possessing photosymbionts have been found sporadically within phylogenetically distant taxa, such as Opisthokonta and Alveolata, and a limited number of model species have been studied.
Consider removing "Although" since the sentence doesn't continue the thought
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