Price et al. [(1999). J. Bacteriol. 181:2358–2362] conducted a genetic study of the toxin transport protein (PA) of Bacillus anthracis, the bacterium that causes anthrax in humans. Within the 2294-nucleotide gene in 26 strains they identified five point mutations—two missense and three synonyms—among different isolates. Necropsy samples from an anthrax outbreak in 1979 revealed a novel missense mutation and five unique nucleotide changes among ten victims. The authors concluded that these data indicate little or no horizontal transfer between different B. anthracis strains.
What is meant by 'horizontal transfer'?

Verified step by step guidance

1. Understand that 'horizontal transfer' (also called horizontal gene transfer) refers to the movement of genetic material between organisms in a manner other than traditional reproduction (vertical transfer from parent to offspring).
2. Recognize that in bacteria, horizontal transfer can occur through mechanisms such as transformation (uptake of free DNA), transduction (transfer by viruses), or conjugation (direct transfer between cells).
3. Note that horizontal transfer allows bacteria to acquire new genes, such as those for antibiotic resistance or virulence factors, from unrelated strains or species.
4. Contrast horizontal transfer with vertical transfer, which is the inheritance of genes from parent to progeny during cell division.
5. Summarize that in the context of the problem, 'little or no horizontal transfer' means that the genetic differences observed among the Bacillus anthracis strains likely arose through mutation and vertical inheritance rather than gene exchange between strains.

Key Concepts

Horizontal Gene Transfer

Horizontal gene transfer (HGT) is the movement of genetic material between organisms other than by descent from parent to offspring. It allows bacteria to acquire new genes, such as antibiotic resistance, from unrelated strains or species. HGT contrasts with vertical transfer, which is inheritance through reproduction.

Point Mutations (Missense and Synonymous)

Point mutations are changes in a single nucleotide of DNA. Missense mutations alter the amino acid sequence of a protein, potentially affecting its function, while synonymous mutations do not change the amino acid sequence and are often neutral. These mutations help track genetic variation among strains.

Genetic Variation and Strain Differentiation

Genetic variation refers to differences in DNA sequences among individuals or strains. Identifying unique mutations in bacterial strains helps distinguish them and understand their evolutionary relationships. Limited variation and lack of shared mutations suggest minimal gene exchange between strains.