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Abstract
Exposure of bacteria to sublethal concentrations of antibiotics can lead to bacterial adaptation and survival at higher doses of inhibitors, which in turn can lead to the emergence of antibiotic resistance. The presence of sublethal concentrations of antibiotics targeting translation results in an increase in the amount of ribosomes per cell but nonetheless a decrease in the cells’ growth rate. In this work, we have found that inhibition of ribosome activity can result in a decrease in the amount of free RNA polymerase available for transcription, thus limiting the protein expression rate via a different pathway than what was expected. This result can be explained by our observation that long genes, such as those coding for RNA polymerase subunits, have a higher probability of premature translation termination in the presence of ribosome inhibitors, while expression of short ribosomal genes is affected less, consistent with their increased concentration. In bacterial cells, inhibition of ribosomes by sublethal concentrations of antibiotics leads to a decrease in the growth rate despite an increase in ribosome content. The limitation of ribosomal activity results in an increase in the level of expression from ribosomal promoters; this can deplete the pool of RNA polymerase (RNAP) that is available for the expression of nonribosomal genes. However, the magnitude of this effect remains to be quantified. Here, we use the change in the activity of constitutive promoters with different affinities for RNAP to quantify the change in the concentration of free RNAP. The data are consistent with a significant decrease in the amount of RNAP available for transcription of both ribosomal and nonribosomal genes. Results obtained with different reporter genes reveal an mRNA length dependence on the amount of full-length translated protein, consistent with the decrease in ribosome processivity affecting more strongly the translation of longer genes. The genes coding for the β and β' subunits of RNAP are among the longest genes in the Escherichia coli genome, while the genes coding for ribosomal proteins are among the shortest genes. This can explain the observed decrease in transcription capacity that favors the expression of genes whose promoters have a high affinity for RNAP, such as ribosomal promoters. IMPORTANCE Exposure of bacteria to sublethal concentrations of antibiotics can lead to bacterial adaptation and survival at higher doses of inhibitors, which in turn can lead to the emergence of antibiotic resistance. The presence of sublethal concentrations of antibiotics targeting translation results in an increase in the amount of ribosomes per cell but nonetheless a decrease in the cells’ growth rate. In this work, we have found that inhibition of ribosome activity can result in a decrease in the amount of free RNA polymerase available for transcription, thus limiting the protein expression rate via a different pathway than what was expected. This result can be explained by our observation that long genes, such as those coding for RNA polymerase subunits, have a higher probability of premature translation termination in the presence of ribosome inhibitors, while expression of short ribosomal genes is affected less, consistent with their increased concentration.
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Baumstark R, Hänzelmann S, Tsuru S, Schaerli Y, Francesconi M, Mancuso FM, Castelo R, Isalan M. The propagation of perturbations in rewired bacterial gene networks. Nat Commun 2015; 6:10105. [PMID: 26670742 DOI: 10.1038/ncomms10105] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/05/2015] [Accepted: 11/04/2015] [Indexed: 11/09/2022] Open
Abstract
What happens to gene expression when you add new links to a gene regulatory network? To answer this question, we profile 85 network rewirings in E. coli. Here we report that concerted patterns of differential expression propagate from reconnected hub genes. The rewirings link promoter regions to different transcription factor and σ-factor genes, resulting in perturbations that span four orders of magnitude, changing up to ∼ 70% of the transcriptome. Importantly, factor connectivity and promoter activity both associate with perturbation size. Perturbations from related rewirings have more similar transcription profiles and a statistical analysis reveals ∼ 20 underlying states of the system, associating particular gene groups with rewiring constructs. We examine two large clusters (ribosomal and flagellar genes) in detail. These represent alternative global outcomes from different rewirings because of antagonism between these major cell states. This data set of systematically related perturbations enables reverse engineering and discovery of underlying network interactions.
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Affiliation(s)
- Rebecca Baumstark
- EMBL/CRG Systems Biology Research Unit, Centre for Genomic Regulation (CRG), Dr Aiguader 88, 08003 Barcelona, Spain.,Universitat Pompeu Fabra (UPF), Dr Aiguader 88, 08003 Barcelona, Spain
| | - Sonja Hänzelmann
- Research Program on Biomedical Informatics (GRIB), Hospital del Mar Medical Research Institute (IMIM), Dr Aiguader 88, 08003 Barcelona, Spain.,Department of Experimental and Health Sciences, Universitat Pompeu Fabra, Dr Aiguader 88, 08003 Barcelona, Spain
| | - Saburo Tsuru
- Department of Bioinformatic Engineering, Graduate School of Information Science and Technology, Osaka University, 1-5 Yamadaoka, Suita, Osaka 565-0871, Japan
| | - Yolanda Schaerli
- EMBL/CRG Systems Biology Research Unit, Centre for Genomic Regulation (CRG), Dr Aiguader 88, 08003 Barcelona, Spain.,Universitat Pompeu Fabra (UPF), Dr Aiguader 88, 08003 Barcelona, Spain
| | - Mirko Francesconi
- EMBL/CRG Systems Biology Research Unit, Centre for Genomic Regulation (CRG), Dr Aiguader 88, 08003 Barcelona, Spain.,Universitat Pompeu Fabra (UPF), Dr Aiguader 88, 08003 Barcelona, Spain
| | - Francesco M Mancuso
- EMBL/CRG Systems Biology Research Unit, Centre for Genomic Regulation (CRG), Dr Aiguader 88, 08003 Barcelona, Spain.,Genomics Cancer Group, Vall d 'Hebron Institute of Oncology (VHIO), Carrer Natzaret 15-17, 08035 Barcelona, Spain
| | - Robert Castelo
- Research Program on Biomedical Informatics (GRIB), Hospital del Mar Medical Research Institute (IMIM), Dr Aiguader 88, 08003 Barcelona, Spain.,Department of Experimental and Health Sciences, Universitat Pompeu Fabra, Dr Aiguader 88, 08003 Barcelona, Spain
| | - Mark Isalan
- EMBL/CRG Systems Biology Research Unit, Centre for Genomic Regulation (CRG), Dr Aiguader 88, 08003 Barcelona, Spain.,Universitat Pompeu Fabra (UPF), Dr Aiguader 88, 08003 Barcelona, Spain.,Department of Life Sciences, Imperial College London, London SW7 2AZ, UK
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Ehrenberg M, Bremer H, Dennis PP. Medium-dependent control of the bacterial growth rate. Biochimie 2012; 95:643-58. [PMID: 23228516 DOI: 10.1016/j.biochi.2012.11.012] [Citation(s) in RCA: 50] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/31/2012] [Accepted: 11/22/2012] [Indexed: 11/26/2022]
Abstract
By combining results from previous studies of nutritional up-shifts we here re-investigate how bacteria adapt to different nutritional environments by adjusting their macromolecular composition for optimal growth. We demonstrate that, in contrast to a commonly held view the macromolecular composition of bacteria does not depend on the growth rate as an independent variable, but on three factors: (i) the genetic background (i.e. the strain used), (ii) the physiological history of the bacteria used for inoculation of a given growth medium, and (iii) the kind of nutrients in the growth medium. These factors determine the ribosome concentration and the average rate of protein synthesis per ribosome, and thus the growth rate. Immediately after a nutritional up-shift, the average number of ribosomes in the bacterial population increases exponentially with time at a rate which eventually is attained as the final post-shift growth rate of all cell components. After a nutritional up-shift from one minimal medium to another minimal medium of higher nutritional quality, ribosome and RNA polymerase syntheses are co-regulated and immediately increase by the same factor equal to the increase in the final growth rate. However, after an up-shift from a minimal medium to a medium containing all 20 amino acids, RNA polymerase and ribosome syntheses are no longer coregulated; a smaller rate of synthesis of RNA polymerase is compensated by a gradual increase in the fraction of free RNA polymerase, possibly due to a gradual saturation of mRNA promoters. We have also analyzed data from a recent publication, in which it was concluded that the macromolecular composition in terms of RNA/protein and RNA/DNA ratios is solely determined by the effector molecule ppGpp. Our analysis indicates that this is true only in special cases and that, in general, medium adaptation also depends on factors other than ppGpp.
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Affiliation(s)
- Måns Ehrenberg
- Department of Cell and Molecular Biology, BMC, Uppsala University, Box 596, S-751 24 Uppsala, Sweden.
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Kanjee U, Ogata K, Houry WA. Direct binding targets of the stringent response alarmone (p)ppGpp. Mol Microbiol 2012; 85:1029-43. [PMID: 22812515 DOI: 10.1111/j.1365-2958.2012.08177.x] [Citation(s) in RCA: 126] [Impact Index Per Article: 10.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023]
Abstract
The Escherichia coli stringent response, mediated by the alarmone ppGpp, is responsible for the reorganization of cellular transcription upon nutritional starvation and other stresses. These transcriptional changes occur mainly as a result of the direct effects of ppGpp and its partner transcription factor DksA on RNA polymerase. An often overlooked feature of the stringent response is the direct targeting of other proteins by ppGpp. Here we review the literature on proteins that are known to bind ppGpp and, based on sequence homology, X-ray crystal structures and in silico docking, we propose new potential protein binding targets for ppGpp. These proteins were found to fall into five main categories: (i) cellular GTPases, (ii) proteins involved in nucleotide metabolism, (iii) proteins involved in lipid metabolism, (iv) general metabolic proteins and (v) PLP-dependent basic aliphatic amino acid decarboxylases. Bioinformatic rationale is provided for expanding the role of ppGpp in regulating the activities of the cellular GTPases. Proteins involved in nucleotide and lipid metabolism and general metabolic proteins provide an interesting set of structurally varied stringent response targets. While the inhibition of some PLP-dependent decarboxylases by ppGpp suggests the existence of cross-talk between the acid stress and stringent response systems.
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Affiliation(s)
- Usheer Kanjee
- Department of Biochemistry, University of Toronto, Toronto, Ontario M5S 1A8, Canada
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Cardinale S, Arkin AP. Contextualizing context for synthetic biology--identifying causes of failure of synthetic biological systems. Biotechnol J 2012; 7:856-66. [PMID: 22649052 PMCID: PMC3440575 DOI: 10.1002/biot.201200085] [Citation(s) in RCA: 251] [Impact Index Per Article: 20.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/10/2012] [Revised: 04/12/2012] [Accepted: 05/04/2012] [Indexed: 12/19/2022]
Abstract
Despite the efforts that bioengineers have exerted in designing and constructing biological processes that function according to a predetermined set of rules, their operation remains fundamentally circumstantial. The contextual situation in which molecules and single-celled or multi-cellular organisms find themselves shapes the way they interact, respond to the environment and process external information. Since the birth of the field, synthetic biologists have had to grapple with contextual issues, particularly when the molecular and genetic devices inexplicably fail to function as designed when tested in vivo. In this review, we set out to identify and classify the sources of the unexpected divergences between design and actual function of synthetic systems and analyze possible methodologies aimed at controlling, if not preventing, unwanted contextual issues.
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Affiliation(s)
- Stefano Cardinale
- Physical Biosciences Division, LBNL, Department of Bioengineering, University of California, Berkeley, CA, USA
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Abstract
The assembly of bacterial ribosomes is viewed with increasing interest as a potential target for new antibiotics. The in vivo synthesis and assembly of ribosomes are briefly reviewed here, highlighting the many ways in which assembly can be perturbed. The process is compared with the model in vitro process from which much of our knowledge is derived. The coordinate synthesis of the ribosomal components is essential for their ordered and efficient assembly; antibiotics interfere with this coordination and therefore affect assembly. It has also been claimed that the binding of antibiotics to nascent ribosomes prevents their assembly. These two contrasting models of antibiotic action are compared and evaluated. Finally, the suitability and tractability of assembly as a drug target are assessed.
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Bremer H, Dennis P. Feedback control of ribosome function in Escherichia coli. Biochimie 2007; 90:493-9. [PMID: 17999920 DOI: 10.1016/j.biochi.2007.10.008] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/19/2007] [Accepted: 10/20/2007] [Indexed: 11/19/2022]
Abstract
We have previously proposed that the rate of ribosome function during balanced growth in E. coli, expressed as the rate of peptide chain elongation, is adjusted by a feedback mechanism: whenever that rate is submaximal (i.e. below 22 amino acid residues polymerized per active ribosome at 37 degrees C), the feedback signal ppGpp is generated by an activation of the ppGpp synthetase expressed from the spoT gene. The accumulation of ppGpp reduces the synthesis of additional ribosomes and thereby reduces the consumption of amino acids which, in turn, allows the remaining ribosomes to function at a higher rate. Here we have described with supporting evidence the proposed feedback loop in greater detail and provided a mathematical analysis which predicts that the SpoT ppGpp synthetase activity should be highest when the ribosomes function at their half-maximal rate. This prediction is consistent with reported observations and is independent of the particular (unknown) mechanism by which the rate of translation controls the ppGpp synthetase activity of SpoT.
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Affiliation(s)
- H Bremer
- Department of Molecular and Cell Biology, University of Texas at Dallas, Richardson, TX 75083-0688, USA.
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