Question 1

Are reporter strains enough to identify a signal?

Accepted Answer

No. Biosensor strains respond to whole families of related molecules with differing sensitivity, so a positive signal only narrows the candidates. Chemical confirmation by liquid chromatography with tandem mass spectrometry, ideally against synthetic standards, is what establishes which molecule the producing strain actually makes.

Question 2

How should signal concentration be normalised?

Accepted Answer

Report it per cell or against optical density rather than per unit volume at fixed times. The central claim concerns density dependence, so plotting signal against viable counts across the growth curve, in parallel cultures sampled repeatedly, keeps the comparison meaningful across strains and media.

Question 3

What genetic evidence links a signal to a target gene?

Accepted Answer

A synthase mutant should lose target expression, exogenous addition of the purified molecule should restore it in a dose-dependent way, and a receptor mutant should stay unresponsive even with the signal supplied. Complementation returning both phenotypes closes the argument against secondary mutations.

Question 4

Why measure responses at single-cell resolution?

Accepted Answer

Bulk averages can hide bimodal switching, where part of the population responds strongly and the rest not at all. Fluorescent promoter fusions read by microscopy or flow cytometry reveal that distribution, which matters for claims about coordination and for fitting threshold models to the data.

Question 5

How are peptide signals handled differently?

Accepted Answer

Peptide autoinducers need processing and export, and often carry ring or thiolactone structures that complicate synthesis and storage. Detection relies on mass spectrometry rather than lactone biosensors, and receptor work centres on membrane histidine kinases, so the assay set differs substantially from the lactone systems.

Question 6

Does signal interference belong in this kind of project?

Accepted Answer

It fits well as a test of mechanism. Enzymes that degrade lactones or receptor antagonists should abolish the response without slowing growth, and that growth control is essential. Without it, an apparent interference effect may simply reflect general toxicity to the culture.

Microbiology

Microbiology

Research Frontiers in Bacterial Autoinducers and Density-Dependent Signaling