Fate of donor deoxyribonucleic acid in a highly transformation-deficient strain of Haemophilus influenzae

Area of Science:

• Microbiology
• Molecular Biology
• Genetics

Background:

• Transformation is a key process for genetic exchange in bacteria like Haemophilus influenzae.
• DNA repair mechanisms, such as those involving RecA, are crucial for maintaining genomic integrity and facilitating genetic recombination.

Purpose of the Study:

• To isolate and characterize a transformation-deficient mutant of Haemophilus influenzae.
• To elucidate the molecular mechanisms underlying DNA integration during bacterial transformation.

Main Methods:

• Isolation of a transformation-deficient mutant (TD24) via selection for mitomycin C sensitivity.
• Genetic mapping of the mutation using antibiotic resistance markers (str-r, nov-r).
• Analysis of donor DNA uptake, intracellular fate, and chromosomal association in wild-type and mutant strains.

Main Results:

• The TD24 mutant exhibited a 10^4-fold decrease in transformation efficiency, similar to recA mutants.
• Donor DNA uptake was normal, but recombinant molecules were not formed.
• While donor DNA associated with the recipient chromosome, fewer donor atoms were integrated, and this was accompanied by loss of donor marker activity.

Conclusions:

• The TD24 mutation impairs a post-uptake step in transformation, distinct from DNA uptake or initial association.
• The data favor a model where donor DNA integration involves local DNA synthesis rather than dispersive recombination.
• This finding provides insights into alternative mechanisms of DNA integration in bacteria.