Ultrastructure and molecular phylogenetic position of a novel euglenozoan with extrusive episymbiotic bacteria: Bihospites bacati n. gen. et sp. (Symbiontida)
Why this work is in the frame
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Bibliographic record
Abstract
BACKGROUND: Poorly understood but highly diverse microbial communities exist within anoxic and oxygen-depleted marine sediments. These communities often harbour single-celled eukaryotes that form symbiotic associations with different prokaryotes. During low tides in South-western British Columbia, Canada, vast areas of marine sand become exposed, forming tidal pools. Oxygen-depleted sediments within these pools are distinctively black at only 2-3 cm depth; these layers contain a rich variety of microorganisms, many of which are undescribed. We discovered and characterized a novel (uncultivated) lineage of heterotrophic euglenozoan within these environments using light microscopy, scanning and transmission electron microscopy, serial sectioning and ultrastructural reconstruction, and molecular phylogenetic analyses of small subunit rDNA sequences. RESULTS: Bihospites bacati n. gen. et sp. is a biflagellated microbial eukaryote that lives within low-oxygen intertidal sands and dies within a few hours of exposure to atmospheric oxygen. The cells are enveloped by two different prokaryotic episymbionts: (1) rod-shaped bacteria and (2) longitudinal strings of spherical bacteria, capable of ejecting an internal, tightly wound thread. Ultrastructural data showed that B. bacati possesses all of the euglenozoan synapomorphies. Moreover, phylogenetic analyses of SSU rDNA sequences demonstrated that B. bacati groups strongly with the Symbiontida: a newly established subclade within the Euglenozoa that includes Calkinsia aureus and other unidentified organisms living in low-oxygen sediments. B. bacati also possessed novel features, such as a compact C-shaped rod apparatus encircling the nucleus, a cytostomal funnel and a distinctive cell surface organization reminiscent of the pellicle strips in phagotrophic euglenids. CONCLUSIONS: We characterized the ultrastructure and molecular phylogenetic position of B. bacati n. gen. et sp. Molecular phylogenetic analyses demonstrated that this species belongs to the Euglenozoa and currently branches as the earliest diverging member of the Symbiontida. This is concordant with ultrastructural features of B. bacati that are intermediate between C. aureus and phagotrophic euglenids, indicating that the most recent ancestor of the Symbiontida descended from phagotrophic euglenids. Additionally, the extrusive episymbionts in B. bacati are strikingly similar to so-called "epixenosomes", prokaryotes previously described in a ciliate species and identified as members of the Verrucomicrobia. These parallel symbioses increase the comparative context for understanding the origin(s) of extrusive organelles in eukaryotes and underscores how little we know about the symbiotic communities of marine benthic environments.
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Full frame distilled prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. Learned from the 10,348 direct Codex labels and 10,348 direct Gemma labels. Candidate is the union of thresholded teacher heads; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels or direct frontier model labels.
Codex and Gemma teacher scores by category
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.000 | 0.000 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from it