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  • 1.
    Felletti, Michele
    et al.
    Stockholm University, Faculty of Science, Department of Molecular Biosciences, The Wenner-Gren Institute. Stockholm University, Science for Life Laboratory (SciLifeLab).
    Omnus, Deike J.
    Stockholm University, Faculty of Science, Department of Molecular Biosciences, The Wenner-Gren Institute. Stockholm University, Science for Life Laboratory (SciLifeLab).
    Jonas, Kristina
    Stockholm University, Faculty of Science, Department of Molecular Biosciences, The Wenner-Gren Institute. Stockholm University, Science for Life Laboratory (SciLifeLab).
    Regulation of the replication initiator DnaA in Caulobacter crescentus2019In: Biochimica et Biophysica Acta. Gene Regulatory Mechanisms, ISSN 1874-9399, E-ISSN 1876-4320, Vol. 1862, no 7, p. 697-705Article, review/survey (Refereed)
    Abstract [en]

    The decision to initiate DNA replication is a critical step in the cell cycle of all organisms. In nearly all bacteria, replication initiation requires the activity of the conserved replication initiation protein DnaA. Due to its central role in cell cycle progression, DnaA activity must be precisely regulated. This review summarizes the current state of DnaA regulation in the asymmetrically dividing alpha-proteobacterium Caulobacter crescentus, an important model for bacterial cell cycle studies. Mechanisms will be discussed that regulate DnaA activity and abundance under optimal conditions and in coordination with the asymmetric Caulobacter cell cycle. Furthermore, we highlight recent findings of how regulated DnaA synthesis and degradation collaborate to adjust DnaA abundance under stress conditions. The mechanisms described provide important examples of how DNA replication is regulated in an a-proteobacterium and thus represent an important starting point for the study of DNA replication in many other bacteria. This article is part of a Special Issue entitled: Dynamic gene expression, edited by Prof. Patrick Viollier.

  • 2.
    Heinrich, Kristina
    et al.
    Stockholm University, Faculty of Science, Department of Molecular Biosciences, The Wenner-Gren Institute. Stockholm University, Science for Life Laboratory (SciLifeLab).
    Leslie, David J.
    Stockholm University, Faculty of Science, Department of Molecular Biosciences, The Wenner-Gren Institute. Stockholm University, Science for Life Laboratory (SciLifeLab).
    Morlock, Michaela
    Stockholm University, Faculty of Science, Department of Molecular Biosciences, The Wenner-Gren Institute. Stockholm University, Science for Life Laboratory (SciLifeLab).
    Bertilsson, Stefan
    Jonas, Kristina
    Stockholm University, Faculty of Science, Department of Molecular Biosciences, The Wenner-Gren Institute. Stockholm University, Science for Life Laboratory (SciLifeLab).
    Molecular Basis and Ecological Relevance of Caulobacter Cell Filamentation in Freshwater Habitats2019In: mBio, ISSN 2161-2129, E-ISSN 2150-7511, Vol. 10, no 4, article id e01557-19Article in journal (Refereed)
    Abstract [en]

    All living cells are characterized by certain cell shapes and sizes. Many bacteria can change these properties depending on the growth conditions. The underlying mechanisms and the ecological relevance of changing cell shape and size remain unclear in most cases. One bacterium that undergoes extensive shape-shifting in response to changing growth conditions is the freshwater bacterium Caulobacter crescentus. When incubated for an extended time in stationary phase, a subpopulation of C. crescentus forms viable filamentous cells with a helical shape. Here, we demonstrated that this stationary-phase-induced filamentation results from downregulation of most critical cell cycle regulators and a consequent block of DNA replication and cell division while cell growth and metabolism continue. Our data indicate that this response is triggered by a combination of three stresses caused by prolonged growth in complex medium, namely, the depletion of phosphate, alkaline pH, and an excess of ammonium. We found that these conditions are experienced in the summer months during algal blooms near the surface in freshwater lakes, a natural habitat of C. crescentus, suggesting that filamentous growth is a common response of C. crescentus to its environment. Finally, we demonstrate that when grown in a biofilm, the filamentous cells can reach beyond the surface of the biofilm and potentially access nutrients or release progeny. Altogether, our work highlights the ability of bacteria to alter their morphology and suggests how this behavior might enable adaptation to changing environments.

  • 3.
    Heinrich, Kristina
    et al.
    Stockholm University, Faculty of Science, Department of Molecular Biosciences, The Wenner-Gren Institute. Stockholm University, Science for Life Laboratory (SciLifeLab). Philipps University Marburg, Germany.
    Sobetzko, Patrick
    Jonas, Kristina
    Stockholm University, Faculty of Science, Department of Molecular Biosciences, The Wenner-Gren Institute. Stockholm University, Science for Life Laboratory (SciLifeLab). Philipps University Marburg, Germany.
    A Kinase-Phosphatase Switch Transduces Environmental Information into a Bacterial Cell Cycle Circuit2016In: PLoS Genetics, ISSN 1553-7390, E-ISSN 1553-7404, Vol. 12, no 12, article id e1006522Article in journal (Refereed)
    Abstract [en]

    The bacterial cell cycle has been extensively studied under standard growth conditions. How it is modulated in response to environmental changes remains poorly understood. Here, we demonstrate that the freshwater bacterium Caulobacter crescentus blocks cell division and grows to filamentous cells in response to stress conditions affecting the cell membrane. Our data suggest that stress switches the membrane-bound cell cycle kinase CckA to its phosphatase mode, leading to the rapid dephosphorylation, inactivation and proteolysis of the master cell cycle regulator CtrA. The clearance of CtrA results in downregulation of division and morphogenesis genes and consequently a cell division block. Upon shift to non-stress conditions, cells quickly restart cell division and return to normal cell size. Our data indicate that the temporary inhibition of cell division through the regulated inactivation of CtrA constitutes a growth advantage under stress. Taken together, our work reveals a new mechanism that allows bacteria to alter their mode of proliferation in response to environmental cues by controlling the activity of a master cell cycle transcription factor. Furthermore, our results highlight the role of a bifunctional kinase in this process that integrates the cell cycle with environmental information.

  • 4.
    Leslie, David J.
    et al.
    Philipps University Marburg, Germany; Max Planck Institute for Terrestrial Microbiology, Germany.
    Heinen, Christian
    Philipps University Marburg, Germany, Max Planck Institute for Terrestrial Microbiology, Germany.
    Schramm, Frederic D.
    Philipps University Marburg, Germany.
    Thüring, Marietta
    Philipps University Marburg, Germany.
    Aakre, Christopher D.
    Massachusetts Institute of Technology, United States of America.
    Murray, Sean M.
    Philipps University Marburg, Germany; Max Planck Institute for Terrestrial Microbiology, Germany.
    Laub, Michael T.
    Massachusetts Institute of Technology, United States of America.
    Jonas, Kristina
    Philipps University Marburg, Germany.
    Nutritional Control of DNA Replication Initiation through the Proteolysis and Regulated Translation of DnaA2015In: PLOS Genetics, ISSN 1553-7390, E-ISSN 1553-7404, Vol. 11, no 7, article id e1005342Article in journal (Refereed)
    Abstract [en]

    Bacteria can arrest their own growth and proliferation upon nutrient depletion and under various stressful conditions to ensure their survival. However, the molecular mechanisms responsible for suppressing growth and arresting the cell cycle under such conditions remain incompletely understood. Here, we identify post-transcriptional mechanisms that help enforce a cell-cycle arrest in Caulobacter crescentus following nutrient limitation and during entry into stationary phase by limiting the accumulation of DnaA, the conserved replication initiator protein. DnaA is rapidly degraded by the Lon protease following nutrient limitation. However, the rate of DnaA degradation is not significantly altered by changes in nutrient availability. Instead, we demonstrate that decreased nutrient availability downregulates dnaA translation by a mechanism involving the 5' untranslated leader region of the dnaA transcript; Lon-dependent proteolysis of DnaA then outpaces synthesis, leading to the elimination of DnaA and the arrest of DNA replication. Our results demonstrate how regulated translation and constitutive degradation provide cells a means of precisely and rapidly modulating the concentration of key regulatory proteins in response to environmental inputs.

  • 5.
    Leslie, David J.
    et al.
    Stockholm University, Faculty of Science, Department of Molecular Biosciences, The Wenner-Gren Institute. Stockholm University, Science for Life Laboratory (SciLifeLab).
    Thüring, Marietta
    Wongwattanarat, Sasipa
    Stockholm University, Faculty of Science, Department of Molecular Biosciences, The Wenner-Gren Institute. Stockholm University, Science for Life Laboratory (SciLifeLab).
    Jonas, Kristina
    Stockholm University, Faculty of Science, Department of Molecular Biosciences, The Wenner-Gren Institute. Stockholm University, Science for Life Laboratory (SciLifeLab).
    Regulation of DnaA and DNA replication at the onset of stationary phase in E. coliManuscript (preprint) (Other academic)
  • 6.
    Schramm, Frederic D.
    et al.
    Stockholm University, Faculty of Science, Department of Molecular Biosciences, The Wenner-Gren Institute. Stockholm University, Science for Life Laboratory (SciLifeLab). Philipps University Marburg, Germany.
    Heinrich, Kristina
    Stockholm University, Faculty of Science, Department of Molecular Biosciences, The Wenner-Gren Institute. Stockholm University, Science for Life Laboratory (SciLifeLab). Philipps University Marburg, Germany.
    Thüring, Marietta
    Bernhardt, Jörg
    Jonas, Kristina
    Stockholm University, Faculty of Science, Department of Molecular Biosciences, The Wenner-Gren Institute. Stockholm University, Science for Life Laboratory (SciLifeLab). Philipps University Marburg, Germany.
    An essential regulatory function of the DnaK chaperone dictates the decision between proliferation and maintenance in Caulobacter crescentus2017In: PLoS Genetics, ISSN 1553-7390, E-ISSN 1553-7404, Vol. 13, no 12, article id e1007148Article in journal (Refereed)
    Abstract [en]

    Hsp70 chaperones are well known for their important functions in maintaining protein homeostasis during thermal stress conditions. In many bacteria the Hsp70 homolog DnaK is also required for growth in the absence of stress. The molecular reasons underlying Hsp70 essentiality remain in most cases unclear. Here, we demonstrate that DnaK is essential in the alpha-proteobacterium Caulobacter crescentus due to its regulatory function in gene expression. Using a suppressor screen we identified mutations that allow growth in the absence of DnaK. All mutations reduced the activity of the heat shock sigma factor sigma(32) , demonstrating that the DnaK-dependent inactivation of sigma(32) is a growth requirement. While most mutations occurred in the rpoH gene encoding sigma(32) , we also identified mutations affecting sigma(32) activity or stability in trans, providing important new insight into the regulatory mechanisms controlling sigma(32) activity. Most notably, we describe a mutation in the ATP dependent protease HslUV that induces rapid degradation of sigma(32) , and a mutation leading to increased levels of the house keeping sigma(70) that outcompete sigma(32) for binding to the RNA polymerase. We demonstrate that sigma(32) inhibits growth and that its unrestrained activity leads to an extensive reprogramming of global gene expression, resulting in upregulation of repair and maintenance functions and downregulation of the growth-promoting functions of protein translation, DNA replication and certain metabolic processes. While this re-allocation from proliferative to maintenance functions could provide an advantage during heat stress, it leads to growth defects under favorable conditions. We conclude that Caulobacter has coopted the DnaK chaperone system as an essential regulator of gene expression under conditions when its folding activity is dispensable.

  • 7.
    Schramm, Frederic D.
    et al.
    Stockholm University, Faculty of Science, Department of Molecular Biosciences, The Wenner-Gren Institute. Stockholm University, Science for Life Laboratory (SciLifeLab).
    Schroeder, Kristen
    Stockholm University, Faculty of Science, Department of Molecular Biosciences, The Wenner-Gren Institute. Stockholm University, Science for Life Laboratory (SciLifeLab).
    Alvelid, Jonatan
    Testa, Ilaria
    Jonas, Kristina
    Stockholm University, Faculty of Science, Department of Molecular Biosciences, The Wenner-Gren Institute. Stockholm University, Science for Life Laboratory (SciLifeLab).
    Growth‐driven displacement of protein aggregates along the cell length ensures partitioning to both daughter cells in Caulobacter crescentus2019In: Molecular Microbiology, ISSN 0950-382X, E-ISSN 1365-2958, Vol. 111, no 6, p. 1430-1448Article in journal (Refereed)
    Abstract [en]

    All living cells must cope with protein aggregation, which occurs as a result of experiencing stress. In previously studied bacteria, aggregated protein collects at the cell poles and is retained throughout consecutive cell divisions only in old pole‐inheriting daughter cells, resulting in aggregation‐free progeny within a few generations. In this study we describe the in vivo kinetics of aggregate formation and elimination following heat and antibiotic stress in the asymmetrically dividing bacterium Caulobacter crescentus. Unexpectedly, in this bacterium protein aggregates form as multiple distributed foci located throughout the cell volume. Time‐lapse microscopy revealed that under moderate stress, the majority of these protein aggregates are short‐lived and rapidly dissolved by the major chaperone DnaK and the disaggregase ClpB. Severe stress or genetic perturbation of the protein quality control machinery induces the formation of long‐lived aggregates. Importantly, the majority of persistent aggregates neither collect at the cell poles nor are they partitioned to only one daughter cell type. Instead, we show that aggregates are distributed to both daughter cells in the same ratio at each division, which is driven by the continuous elongation of the growing mother cell. Therefore, our study has revealed a new pattern of protein aggregate inheritance in bacteria.

  • 8.
    Schramm, Frederic D.
    et al.
    Stockholm University, Faculty of Science, Department of Molecular Biosciences, The Wenner-Gren Institute. Stockholm University, Science for Life Laboratory (SciLifeLab).
    Schroeder, Kristen
    Stockholm University, Faculty of Science, Department of Molecular Biosciences, The Wenner-Gren Institute. Stockholm University, Science for Life Laboratory (SciLifeLab).
    Jonas, Kristina
    Stockholm University, Faculty of Science, Department of Molecular Biosciences, The Wenner-Gren Institute. Stockholm University, Science for Life Laboratory (SciLifeLab).
    Protein aggregation in bacteria2020In: FEMS Microbiology Reviews, ISSN 0168-6445, E-ISSN 1574-6976, Vol. 44, no 1, p. 54-72Article, review/survey (Refereed)
    Abstract [en]

    Protein aggregation occurs as a consequence of perturbations in protein homeostasis that can be triggered by environmental and cellular stresses. The accumulation of protein aggregates has been associated with aging and other pathologies in eukaryotes, and in bacteria with changes in growth rate, stress resistance and virulence. Numerous past studies, mostly performed in Escherichia coli, have led to a detailed understanding of the functions of the bacterial protein quality control machinery in preventing and reversing protein aggregation. However, more recent research points toward unexpected diversity in how phylogenetically different bacteria utilize components of this machinery to cope with protein aggregation. Furthermore, how persistent protein aggregates localize and are passed on to progeny during cell division and how their presence impacts reproduction and the fitness of bacterial populations remains a controversial field of research. Finally, although protein aggregation is generally seen as a symptom of stress, recent work suggests that aggregation of specific proteins under certain conditions can regulate gene expression and cellular resource allocation. This review discusses recent advances in understanding the consequences of protein aggregation and how this process is dealt with in bacteria, with focus on highlighting the differences and similarities observed between phylogenetically different groups of bacteria.

  • 9.
    Wassing, Gabriela
    et al.
    Stockholm University, Faculty of Science, Department of Molecular Biosciences, The Wenner-Gren Institute.
    Sigurlásdóttir, Sara
    Stockholm University, Faculty of Science, Department of Molecular Biosciences, The Wenner-Gren Institute.
    Schroeder, Kristen
    Stockholm University, Faculty of Science, Department of Molecular Biosciences, The Wenner-Gren Institute.
    Ilehag, Nathalie
    Stockholm University, Faculty of Science, Department of Molecular Biosciences, The Wenner-Gren Institute.
    Lindås, Ann-Christin
    Stockholm University, Faculty of Science, Department of Molecular Biosciences, The Wenner-Gren Institute.
    Jonas, Kristina
    Stockholm University, Faculty of Science, Department of Molecular Biosciences, The Wenner-Gren Institute.
    Jonsson, Ann-Beth
    Stockholm University, Faculty of Science, Department of Molecular Biosciences, The Wenner-Gren Institute.
    Meningococcal DNA binds to human beta-defensin 2 and blocks its lethal effect against the bacteriaManuscript (preprint) (Other academic)
1 - 9 of 9
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