Identification and characterization of a conserved nuclease secreted by strains of the Lactobacillus casei group
Bibliographic record
Abstract
AIMS: Nuclease secretion was evaluated for five species of Lactobacillus and the activity was characterized in terms of thermal resistance, molecular weight and mode of action on plasmid DNA. METHODS AND RESULTS: Assays of nuclease from L. rhamnosus ATCC 9595 on DNA of different origins indicates a broad activity spectrum. Secreted nuclease from this strain resists a thermal treatment of 20 min at 100 degrees C, is not sensitive to a treatment for disruption of disulphide bonds nor to EDTA treatment under 10 mM l(-1). Nuclease production is not growth linked and seems to be constitutive. Extracellular nuclease of L. rhamnosus ATCC 9595 introduces a single-stranded nick in supercoiled DNA, thus potentially reducing the transformability of plasmid DNA. In seven of eight tested strains, SDS-PAGE revealed a major protein with a molecular weight of ca 35 kDa. Minor degradation products also showed nuclease activity. CONCLUSIONS: A comparative analysis of the extracellular fractions of 14 different Lactobacillus strains indicate that nuclease secretion seems to be a widely distributed function among species of milk-related lactobacilli. The production of secreted nuclease may contribute to the low ability of Lactobacillus spp. to be transformed and maintain exogenous DNA. SIGNIFICANCE AND IMPACT OF THE STUDY: Determination of the characteristics and distribution of nuclease activity contribute to developing strategies to overcome this barrier to efficient transformation of milk lactobacilli.
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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 | 0.001 |
| Meta-epidemiology (narrow) | 0.001 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.001 | 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 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".