Publications by authors named "R D'ari"
Biofilms are structured communities characterized by distinctive gene expression patterns and profound physiological changes compared to those of planktonic cultures. Here, we show that many gram-negative bacterial biofilms secrete high levels of a small-molecular-weight compound, which inhibits the growth of only Escherichia coli K-12 and a rare few other natural isolates. We demonstrate both genetically and biochemically that this molecule is the amino acid valine, and we provide evidence that valine production within biofilms results from metabolic changes occurring within high-density biofilm communities when carbon sources are not limiting.
View Article and Find Full Text PDFLuria-Bertani broth supports Escherichia coli growth to an optical density at 600 nm (OD(600)) of 7. Surprisingly, however, steady-state growth ceases at an OD(600) of 0.3, when the growth rate slows down and cell mass decreases.
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- The study investigates the characteristics of bacterial L forms, known to typically lack peptidoglycan, particularly focusing on how they divide.
- Using the beta-lactam cefsulodin, researchers turned wild Escherichia coli K-12 into a state resembling L forms, finding these cells to be spherical and sensitive to osmotic changes.
- Despite appearances, further analysis revealed that these L-form-like cells still require components linked to peptidoglycan synthesis for growth and division, suggesting that even in this altered state, they retain a reduced form of peptidoglycan that is critical for cell division.
The Escherichia coli proteins DksA, GreA, and GreB are all structural homologs that bind the secondary channel of RNA polymerase (RNAP) but are thought to act at different levels of transcription. DksA, with its co-factor ppGpp, inhibits rrnB P1 transcription initiation, whereas GreA and GreB activate RNAP to cleave back-tracked RNA during elongational pausing. Here, in vivo and in vitro evidence reveals antagonistic regulation of rrnB P1 transcription initiation by Gre factors (particularly GreA) and DksA; GreA activates and DksA inhibits.
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- Mecillinam specifically targets penicillin-binding protein 2 (PBP2) in E. coli, which is crucial for maintaining the rod shape of the cells; its inactivation causes a division block.
- A mutation in the fes gene leads to mecillinam resistance in certain E. coli strains by causing increased levels of the signaling molecule ppGpp, which allows cell division even without PBP2 activity.
- The study highlights a regulatory loop where iron limitation increases ppGpp levels, which in turn enhances the expression of iron uptake genes, helping the cells cope with iron scarcity.