Abstract
BackgroundTwo-component signal transduction systems are one means of bacteria to respond to external stimuli. The LiaFSR two-component system of Bacillus subtilis consists of a regular two-component system LiaRS comprising the core Histidine Kinase (HK) LiaS and the Response Regulator (RR) LiaR and additionally the accessory protein LiaF, which acts as a negative regulator of LiaRS-dependent signal transduction. The complete LiaFSR system was shown to respond to various peptide antibiotics interfering with cell wall biosynthesis, including bacitracin.Methodology and Principal FindingsHere we study the response of the LiaFSR system to various concentrations of the peptide antibiotic bacitracin. Using quantitative fluorescence microscopy, we performed a whole population study analyzed on the single cell level. We investigated switching from the non-induced ‘OFF’ state into the bacitracin-induced ‘ON’ state by monitoring gene expression of a fluorescent reporter from the RR-regulated liaI promoter. We found that switching into the ‘ON’ state occurred within less than 20 min in a well-defined switching window, independent of the bacitracin concentration. The switching rate and the basal expression rate decreased at low bacitracin concentrations, establishing clear heterogeneity 60 min after bacitracin induction. Finally, we performed time-lapse microscopy of single cells confirming the quantitative response as obtained in the whole population analysis for high bacitracin concentrations.ConclusionThe LiaFSR system exhibits an immediate, heterogeneous and graded response to the inducer bacitracin in the exponential growth phase.
Highlights
Two-component systems (TCS) are a fundamental principle of bacterial signal transduction that enables cells to respond to environmental stimuli [1,2,3]
Using quantitative fluorescence microscopy [33,34], we focused on a whole population study analyzed at the single cell level
While expression levels from PliaI increased with the externally provided bacitracin amount, we found the immediate response of the LiaFSR system independent of the antibiotic concentration
Summary
Two-component systems (TCS) are a fundamental principle of bacterial signal transduction that enables cells to respond to environmental stimuli [1,2,3]. These phosphotransfer systems involve two conserved components, a histidine protein kinase (HK) and a response regulator protein (RR). The RR, in its ‘active’ form, elicits the specific response Bacteria such as Escherichia coli or Bacillus subtilis posses about 30 HKs and RRs [5,6], including well-known systems such as the EnvZ/ OmpR TCS of the osmosensing pathway [7] or the HK CheA of the chemotaxis system phosphorylating two RRs, CheB and CheY [8]. The complete LiaFSR system was shown to respond to various peptide antibiotics interfering with cell wall biosynthesis, including bacitracin
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