Point mutations in a peptidoglycan biosynthesis gene cause competence induction in Haemophilus influenzae
1Department of Zoology, University of British Columbia, Vancouver, Canada.
Abstract:
We have identified three new Haemophilus influenzae mutations causing cells to exhibit extreme hypercompetence at all stages of growth. The mutations are in murE, which encodes the meso-diaminopimelate-adding enzyme of peptidoglycan synthesis. All are point mutations causing nonconservative amino acid substitutions, two at a poorly conserved residue (G(435)-->R and G(435)-->W) and the third at a highly conserved leucine (L(361)-->S). The mutant strains have very similar phenotypes and do not exhibit any defects in cell growth, permeability, or sensitivity to peptidoglycan antibiotics. Cells retain the normal specificity of DNA uptake for the H. influenzae uptake signal sequence. The mutations do not bypass genes known to be needed for competence induction but do dramatically increase expression of genes required for the normal pathway of DNA uptake. We conclude that the mutations do not act by increasing cell permeability but by causing induction of the normal competence pathway via a previously unsuspected signal.
Insights
Three new Haemophilus influenzae mutations in murE cause extreme hypercompetence. These genetic changes dramatically increase DNA uptake pathway gene expression, suggesting a novel induction signal.
Area of Science:
- Microbiology
- Bacterial genetics
- Molecular biology
Background:
- Haemophilus influenzae is a facultative anaerobic bacterium.
- Bacterial competence is a state of DNA uptake.
- Peptidoglycan synthesis is essential for bacterial cell structure.
Purpose of the Study:
- To identify genetic mutations in Haemophilus influenzae that lead to enhanced cellular competence.
- To investigate the mechanism by which these mutations affect competence and DNA uptake.
Main Methods:
- Genetic analysis of Haemophilus influenzae strains.
- Identification of mutations in the murE gene.
- Phenotypic characterization of mutant strains, including growth, permeability, and DNA uptake specificity.
- Analysis of gene expression related to competence pathways.
Main Results:
- Three point mutations in the murE gene were identified, causing extreme hypercompetence in Haemophilus influenzae.
- Mutations resulted in nonconservative amino acid substitutions in the peptidoglycan synthesis enzyme.
- Mutant strains showed no defects in growth, permeability, or antibiotic sensitivity.
- Mutations significantly increased the expression of genes involved in the normal DNA uptake pathway.
- DNA uptake specificity for the H. influenzae uptake signal sequence was retained.
Conclusions:
- The identified murE mutations induce hypercompetence by upregulating the normal DNA uptake pathway, not by altering cell permeability.
- A previously unrecognized signal likely mediates competence induction through these mutations.
- These findings provide new insights into the regulation of genetic transformation in bacteria.
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