Bacterial Epigenetics
One-Sentence Definition
Bacterial epigenetics refers to heritable (or quasi-heritable) phenotypic changes driven by DNA methylation and related marks without altering the primary DNA sequence — often via phase-variable methyltransferases that reprogram regulons (phasevarions).
Simple Explanation
Bacteria can flip gene programs with chemical tags on DNA, not just by mutating letters — like switching accents without rewriting the book.
Detailed Scientific Explanation
| Mark / system | Effect |
|---|---|
| Dam / CcrM methylation | Replication timing, mismatch repair, virulence gene control (E. coli, Caulobacter) |
| R–M methyltransferases | Self vs non-self + gene regulation (Restriction-Modification Systems) |
| Phasevarions | ON/OFF switching of MTase specificity → genome-wide expression shifts |
| Adenine vs cytosine methylation | Different sequence contexts; readable by SMRT/ONT |
Pathogen examples: Haemophilus, Neisseria, Helicobacter, Streptococcus phasevarions altering adhesion, immune evasion, and antibiotic stress responses (Antigenic Variation overlap).
Mechanism
MTase methylates specific motifs → alters DNA-protein binding → transcription changes → phenotype switch; phase variation of mod genes randomly reorients the system in progeny.
Clinical Importance
- Explains rapid phenotypic heterogeneity within a genetically “same” clone during infection.
- May affect vaccine antigen display and colonization success.
Research Importance
- Methylomes from Long-Read and Hybrid Bacterial Assembly / SMRT sequencing.
- Epigenetic contribution to persistence and biofilm traits.
Diagnostic Relevance
- Emerging: methylation signatures as typing adjuncts; not routine clinical AST.
AMR Relevance
Indirect — phasevarions can change envelope and stress programs that shift MICs or tolerance without new resistance ORFs (Persisters and Antibiotic Tolerance).
Related Methods
Related MOCs
Active Recall Questions
- What is a phasevarion?
- How can ONT/SMRT reveal bacterial epigenetics?
- Why might two isolates with identical assemblies behave differently in adhesion assays?