A unique symbiosome in an anaerobic single-celled eukaryote
Bibliographic record
Abstract
Abstract Symbiotic relationships drive evolutionary change and are important sources of novelty. Here we demonstrate a highly structured syntrophic symbiosis between species of the anaerobic protist Anaeramoeba (Anaeramoebae, Metamonada) and bacterial ectosymbionts. We dissected this symbiosis with long-read metagenomics, transcriptomics of host and symbiont cells coupled with fluorescent in situ hybridization (FISH), and microscopy. Genome sequencing, phylogenomic analyses and FISH show that the symbionts belong to the Desulfobacteraceae and were acquired independently in two different Anaeramoeba species. We show that ectosymbionts likely reside deep within cell surface invaginations in a symbiosomal membrane network that is tightly associated with cytoplasmic hydrogenosomes. Metabolic reconstructions based on the genomes and transcriptomes of the symbionts suggest a highly evolved syntrophic interaction. Host hydrogenosomes likely produce hydrogen, acetate, and propionate that are consumed by the symbionts dissimilatory sulfate reduction, Wood-Ljungdahl and methylmalonyl pathways, respectively. Because the host genome sequences encode several vitamin B12-dependent enzymes but appear to lack the ability to biosynthesize this vitamin, we hypothesize that the symbionts supply their hosts with B12. We detected numerous lateral gene transfers from diverse bacteria to Anaeramoeba , including genes involved in oxygen defense and anaerobic metabolism. Gene families encoding membrane-trafficking components that regulate the phagosomal maturation machinery are notably expanded in Anaeramoeba spp. and may be involved in organizing and/or stabilizing the symbiosomal membrane system. Overall, the Anaeramoebae have evolved a dynamic symbiosome comprised of a vacuolar system that facilitates positioning and maintenance of sulfate-reducing bacterial ectosymbionts.
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How this classification was reachedexpand
Full frame machine prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. The Gemma side is a direct model label for every work in the frame, read from the title-only record. The Codex side is a classifier learned from the 10,348 direct Codex labels and calibrated to design-weighted sample rates; fields without enough sample support carry no Codex call. Candidate is the union of the two sides; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels.
Distilled classifier scores by category (both heads)
| 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 | 0.001 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.001 | 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 itClassification
machine, unvalidatedMachine predicted; a candidate call from one source (direct Gemma or distilled Codex), not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".