Assembly of the <i>Mycobacterium tuberculosis</i> type VII ESX-1 secretion system in <i>Mycobacterium smegmatis</i> identifies a new transcriptional activator of <i>esx-1</i> genes and a novel TB vaccine
Bibliographic record
Abstract
ABSTRACT Mycobacterium tuberculosis ( M. tb ) uses its type VII secretion system (T7SS) ESX-1 to export immunogenic, virulence-mediating protein effectors. In this study, the fast-growing, non-pathogenic model mycobacteria Mycobacterium smegmatis mc 2 -155 was engineered to express the M. tb T7SS ESX-1 system. We found that M. smegmatis transformed with M. tb esx-1 locus genes only, as well as M. smegmatis transformed with M. tb esx-1 and espACD operon genes (designated MSX-1), produces and secretes the M. tb ESX-1 protein effectors EsxA, EsxB, and EspB. However, the abundance of these proteins was higher inside the cell and culture filtrate of the MSX-1 strain. Although ESX-1 is critical for M. tb pathogenesis, expression of M. tb ESX-1 did not make the recombinant M. smegmatis strains virulent in macrophages. Serendipitously, transformation of M. smegmatis with a modified esx-1 locus in this study revealed rv3860 , a gene of previously unknown function, to be required for the transcription of pe35 , ppe68 , esxB, and esxA genes. Finally, mice vaccinated with MSX-1 were found to be as protected as mice vaccinated with Mycobacterium bovis BCG against M. tb infection, without becoming sensitized to tuberculin. These results show that a functional M. tb ESX-1 system can be assembled in M. smegmatis to uncover novel facets of the secretion machinery and that the modified M. smegmatis strain can function as a tuberculosis (TB) vaccine. Unlike BCG, however, its deployment may be compatible with tests currently used to diagnose TB. IMPORTANCE In this study, we modified Mycobacterium smegmatis , which is often used as a surrogate model organism in mycobacterial research, to produce and assemble a functional Mycobacterium tuberculosis ( M. tb ) ESX-1 protein secretion system. One such M. smegmatis strain named MSX-1 was found to make a functional M. tb ESX-1 system without becoming virulent. And in using M. smegmatis as a chassis to study the ESX-1 system, we found that rv3860 , an M. tb gene of previously unknown function, is needed for the production of key ESX-1 proteins. Finally, mice vaccinated with MSX-1 were as protected from tuberculosis (TB) as mice given BCG, the only approved TB vaccine. Notably, we found that unlike BCG, MSX-1 does not sensitize mice to the antigens used in existing TB diagnostic tests. These observations, taken together, highlight the utility of M. smegmatis as a chassis to study the M. tb ESX-1 secretion machinery.
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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) | 0.001 | 0.000 |
| Bibliometrics | 0.000 | 0.001 |
| 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 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".