Isolation of <i>Streptomyces</i> sp. PCB7, the first microorganism demonstrating high-affinity uptake of tropospheric H2
Bibliographic record
Abstract
Microbial-mediated soil uptake accounts for approximately 80% of the global tropospheric dihydrogen (H(2)) sinks. Studies conducted over the last three decades provide indirect evidences that H(2) soil uptake is mediated by free soil hydrogenases or by unknown microorganisms that have a high affinity for H(2). The exact nature of these hypothetical free soil enzymes or of H(2)-consuming microorganisms remains elusive because the activity has never been observed in pure culture. Here, we present the first aerobic microorganism able to consume tropospheric H(2) at ambient levels. A dynamic microcosm chamber was developed to enrich a microbial consortium with a high affinity for H(2), from which selected bacterial and fungal strains were isolated and tested for H(2) uptake. Strain PCB7 had a H(2) consumption activity that followed a Michaelis-Menten kinetics, with an apparent K(m) of 11 p.p.m.v. and a H(2) threshold concentration <0.100 p.p.m.v., corresponding to the high-affinity uptake of tropospheric H(2) observed in soil. 16S ribosomal RNA gene sequences showed that strain PCB7 is highly related to several Streptomyces species. H(2) consumption occurred during the sporulation period of the bacterium. Addition of nickel increased the activity, suggesting that the enzymes involved in H(2) consumption belong to the NiFe uptake class of hydrogenases. Because this is the first microorganism showing a high-affinity uptake of tropospheric H(2), we anticipate that Streptomyces sp. PCB7 will become a model organism for the understanding of the environmental factors influencing H(2) soil uptake.
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How this classification was reachedexpand
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 | 0.001 | 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 | 0.001 | 0.001 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.001 | 0.000 |
| Research integrity | 0.000 | 0.001 |
| Insufficient payload (model declined to judge) | 0.004 | 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 teacher head, 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".