Question 1

Why do spot assays overstate the host range of a phage?

Accepted Answer

Concentrated lysates can clear a lawn through lysis from without or through enzymes carried in the preparation, without any productive infection. Efficiency of plating with serial dilutions, confirmed by progeny recovery from the cleared zone, distinguishes genuine replication from surface killing and should anchor every host range table.

Question 2

How is the surface receptor for a new phage identified?

Accepted Answer

The usual route is selecting resistant derivatives, sequencing their genomes, and testing whether restoring the candidate gene restores sensitivity. Adsorption assays on the mutant confirm the block occurs at binding. Purified receptor competition or binding of labelled tail proteins adds direct evidence beyond the genetic argument.

Question 3

How can adsorption blocks be separated from intracellular defences?

Accepted Answer

Measure adsorption directly by counting unbound particles over time, then quantify genome entry using nucleic acid detection inside the cell. If the phage binds and injects but no progeny appear, restriction systems, CRISPR immunity or abortive infection are the likely obstacles rather than receptor recognition.

Question 4

How large should the bacterial panel be?

Accepted Answer

Size follows the claim being made. Mechanism studies work with a small, well characterised set including isogenic surface mutants. Ecological or therapeutic matching questions need dozens of isolates with recorded serotype, sequence type and origin, since conclusions about breadth depend heavily on how the collection was assembled.

Question 5

What does structural work add to host range studies?

Accepted Answer

Structures of receptor-binding proteins reveal the loops and pockets that contact the surface molecule, turning a broad genetic mapping into residue-level explanation. Predicted models now cover many tail proteins, but predictions need testing through site-directed variants and chimeric constructs before mechanistic claims are made.

Question 6

Can host range be predicted from genome sequence alone?

Accepted Answer

Sequence-based tools give useful shortlists, especially within well sampled phage groups, but they train on uneven data and often miss defence systems in the host. Treat predictions as hypotheses to test experimentally, and report both matches and mismatches so the limits of the method stay visible.

Microbiology

Microbiology

Research Frontiers in Bacteriophage Host Range Determinants