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Positive feedback and noise activate the stringent response regulator rel in mycobacteria.

ABSTRACT: Phenotypic heterogeneity in an isogenic, microbial population enables a subset of the population to persist under stress. In mycobacteria, stresses like nutrient and oxygen deprivation activate the stress response pathway involving the two-component system MprAB and the sigma factor, SigE. SigE in turn activates the expression of the stringent response regulator, rel. The enzyme polyphosphate kinase 1 (PPK1) regulates this pathway by synthesizing polyphosphate required for the activation of MprB. The precise manner in which only a subpopulation of bacterial cells develops persistence, remains unknown. Rel is required for mycobacterial persistence. Here we show that the distribution of rel expression levels in a growing population of mycobacteria is bimodal with two distinct peaks corresponding to low (L) and high (H) expression states, and further establish that a positive feedback loop involving the mprAB operon along with stochastic gene expression are responsible for the phenotypic heterogeneity. Combining single cell analysis by flow cytometry with theoretical modeling, we observe that during growth, noise-driven transitions take a subpopulation of cells from the L to the H state within a "window of opportunity" in time preceding the stationary phase. It is these cells which adapt to nutrient depletion in the stationary phase via the stringent response. We find evidence of hysteresis in the expression of rel in response to changing concentrations of PPK1. Hysteresis promotes robustness in the maintenance of the induced state. Our results provide, for the first time, evidence that bistability and stochastic gene expression could be important for the development of "heterogeneity with an advantage" in mycobacteria and suggest strategies for tackling tuberculosis like targeting transitions from the low to the high rel expression state.

SUBMITTER: Sureka K

PROVIDER: S-EPMC2258413 | biostudies-literature | 2008 Mar

REPOSITORIES: biostudies-literature

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Positive feedback and noise activate the stringent response regulator rel in mycobacteria.

Sureka Kamakshi K Ghosh Bhaswar B Dasgupta Arunava A Basu Joyoti J Kundu Manikuntala M Bose Indrani I

PloS one 20080312 3

Phenotypic heterogeneity in an isogenic, microbial population enables a subset of the population to persist under stress. In mycobacteria, stresses like nutrient and oxygen deprivation activate the stress response pathway involving the two-component system MprAB and the sigma factor, SigE. SigE in turn activates the expression of the stringent response regulator, rel. The enzyme polyphosphate kinase 1 (PPK1) regulates this pathway by synthesizing polyphosphate required for the activation of MprB ...[more]

PMID: 18335046

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Project description:The stringent response is a global bacterial response to nutritional stress mediated by (p)ppGpp. We previously found that both noninfectious Borrelia burgdorferi strain B31 and infectious B. burgdorferi strain N40 produced large amounts of (p)ppGpp during growth in BSK-H medium and suggested that the stringent response was triggered in B. burgdorferi under these conditions. Here we report that (p)ppGpp levels in B. burgdorferi growing in BSK-II or BSK-H medium are not further increased by nutrient limitation or by serine hydroxamate-induced inhibition of protein synthesis and that the presence of (p)ppGpp during growth of N40 in BSK-H medium is not associated with decreased 16S rRNA synthesis. Decreased 16S rRNA synthesis was associated with the decreased growth rate of N40 seen during coculture with tick cells, which are growth conditions that were previously shown to decrease (p)ppGpp levels. One-half as much of the mRNA of the gene encoding the Rel protein of B. burgdorferi (rel(Bbu)) was produced by B31 as by N40 during in vitro growth (2 +/- 0.5 and 4 +/- 0.8 fg of rel(Bbu) mRNA/ng of total Borrelia RNA, respectively). Although the amounts of N40 rel(Bbu) mRNA were identical during growth in vitro and in rat peritoneal chambers, they were markedly decreased during growth in nymphal ticks. In contrast to the lack of change in rel(Bbu) mRNA levels, larger amounts of a 78-kDa protein that was cross-reactive with antibodies to Bacillus subtilis Rel(Bsu) were detected in immunoblots of N40 lysates after growth in rat peritoneal chambers than after growth in vitro. Differences in the level of production of (p)ppGpp between B31 and N40 could not be explained by differences in rel(Bbu) promoters since identical transcriptional start sites 309 nucleotides upstream from the B31 and N40 rel(Bbu) ATG start codon and identical sigma(70)-like promoters were identified by primer extension and sequencing analysis. rel(Bbu) complemented an Escherichia coli CF1693 relA spoT double mutant for growth on M9 minimal medium, and the transformed cells produced rel(Bbu) mRNA. These results indicate that rel(Bbu) is functional and that its transcription and translation and production of (p)ppGpp are affected by environmental conditions in strains N40 and B31. They also suggest that in B. burgdorferi, an organism with few rRNA operons that grows slowly, the role of (p)ppGpp may differ from the classic role played by this molecule in E. coli and that (p)ppGpp may not be responsible for growth rate control.

Dataset Information

Positive feedback and noise activate the stringent response regulator rel in mycobacteria.

Publications

Positive feedback and noise activate the stringent response regulator rel in mycobacteria.

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