Metagenomic analysis suggests broad metabolic potential in extracellular symbionts of the bivalve Thyasira cf. gouldi
Bibliographic record
Abstract
BACKGROUND: Next-generation sequencing has opened new avenues for studying metabolic capabilities of bacteria that cannot be cultured. Here, we provide a metagenomic description of chemoautotrophic gammaproteobacterial symbionts associated with Thyasira cf. gouldi, a sediment-dwelling bivalve from the family Thyasiridae. Thyasirid symbionts differ from those of other bivalves by being extracellular, and recent work suggests that they are capable of living freely in the environment. RESULTS: Thyasira cf. gouldi symbionts appear to form mixed, non-clonal populations in the host, show no signs of genomic reduction and contain many genes that would only be useful outside the host, including flagellar and chemotaxis genes. The thyasirid symbionts may be capable of sulfur oxidation via both the sulfur oxidation and reverse dissimilatory sulfate reduction pathways, as observed in other bivalve symbionts. In addition, genes for hydrogen oxidation and dissimilatory nitrate reduction were found, suggesting varied metabolic capabilities under a range of redox conditions. The genes of the tricarboxylic acid cycle are also present, along with membrane bound sugar importer channels, suggesting that the bacteria may be mixotrophic. CONCLUSIONS: In this study, we have generated the first thyasirid symbiont genomic resources. In Thyasira cf. gouldi, symbiont populations appear non-clonal and encode genes for a plethora of metabolic capabilities; future work should examine whether symbiont heterogeneity and metabolic breadth, which have been shown in some intracellular chemosymbionts, are signatures of extracellular chemosymbionts in bivalves.
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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 | 0.002 | 0.001 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.001 | 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".