Direct observation of type 1 fimbrial switching

The defining feature of bacterial phase variation is a stochastic ‘all‐or‐nothing’ switching in gene expression. However, direct observations of these rare switching events have so far been lacking, obscuring possible correlations between switching events themselves, and between switching and other cellular events, such as division and DNA replication. We monitored the phase variation of type 1 fimbriae in individual Escherichia coli in real time and simultaneously tracked the chromosome replication process. We observed distinctive patterns of fim (fimbriae) expression in multiple genealogically related lineages. These patterns could be explained by a model that combines a single switching event with chromosomal fim replication, as well as the epigenetic inheritance of expressed fim protein and RNA, and their dilution by growth. Analysis of the moment of switching at sub‐cell‐cycle resolution revealed a correlation between fim switching and cell age, which challenges the traditional idea of phase variation as a random Poissonian phenomenon.

[1]  D. Low,et al.  Roles of DNA Adenine Methylation in Regulating Bacterial Gene Expression and Virulence , 2001, Infection and Immunity.

[2]  S. Kanaya,et al.  Sequential binding of SeqA protein to nascent DNA segments at replication forks in synchronized cultures of Escherichia coli , 2004, Molecular microbiology.

[3]  S. Cooper,et al.  Chromosome replication and the division cycle of Escherichia coli B/r. , 1968, Journal of molecular biology.

[4]  J. Plumbridge,et al.  Integrated regulatory responses of fimB to N-acetylneuraminic (sialic) acid and GlcNAc in Escherichia coli K-12. , 2004, Proceedings of the National Academy of Sciences of the United States of America.

[5]  Nancy Kleckner,et al.  SeqA: A negative modulator of replication initiation in E. coli , 1994, Cell.

[6]  H. E. Kubitschek,et al.  Chromosome Replication and the Division Cycle of Escherichia coli B/r , 1971, Journal of bacteriology.

[7]  M. W. van der Woude,et al.  Phase and Antigenic Variation in Bacteria , 2004, Clinical Microbiology Reviews.

[8]  T. Tønjum,et al.  Meningococcal genome dynamics , 2006, Nature Reviews Microbiology.

[9]  François Taddei,et al.  Aging and Death in an Organism That Reproduces by Morphologically Symmetric Division , 2005, PLoS Biology.

[10]  C. Dorman,et al.  Multicopy fim B gene expression in Escherichia coli: binding to inverted repeats in vivo, effect on fimA gene transcription and DNA inversion , 1996, Molecular microbiology.

[11]  I. Blomfield,et al.  Environmental regulation of the fim switch controlling type 1 fimbrial phase variation in Escherichia coli K-12: effects of temperature and media , 1993, Journal of bacteriology.

[12]  N. Sueoka,et al.  Sequential replication of the Bacillus subtilis chromosome. IV. Genetic mapping by density transfer experiment. , 1967, Journal of molecular biology.

[13]  D. Gally,et al.  Regulation of type 1 fimbrial expression in uropathogenic Escherichia coli : heterogeneity of expression through sequence changes in the fim switch region , 1998, Molecular microbiology.

[14]  I. Blomfield.  The regulation of pap and type 1 fimbriation in Escherichia coli. , 2001, Advances in microbial physiology.

[15]  H. Niki,et al.  Bidirectional migration of SeqA‐bound hemimethylated DNA clusters and pairing of oriC copies in Escherichia coli , 2000, Genes to cells : devoted to molecular & cellular mechanisms.

[16]  C. Dorman,et al.  The site‐specific recombination system regulating expression of the Type 1 fimbrial subunit gene of Escherichia coli is sensitive to changes in DNA supercoiling , 1994, Molecular microbiology.

[17]  N. Sueoka,et al.  SEQUENTIAL REPLICATION OF THE BACILLUS SUBTILIS CHROMOSOME. 3. REGULATION OF INITIATION. , 1964, Proceedings of the National Academy of Sciences of the United States of America.

[18]  I. Henderson,et al.  Molecular switches — the ON and OFF of bacterial phase variation , 1999, Molecular microbiology.

[19]  M. Gefter,et al.  DNA replication , 1988, Methods in Molecular Biology.