@article{GongKlumpp2017,
  author    = {Gong, Chen Chris and Klumpp, Stefan},
  title     = {Modeling sRNA-Regulated Plasmid Maintenance},
  series = {PLoS one},
  volume    = {12},
  journal   = {PLoS one},
  publisher = {PLoS},
  address   = {San Fransisco},
  issn      = {1932-6203},
  doi       = {10.1371/journal.pone.0169703},
  pages     = {19},
  year      = {2017},
  abstract  = {We study a theoretical model for the toxin-antitoxin (hok/sok) mechanism for plasmid maintenance in bacteria. Toxin-antitoxin systems enforce the maintenance of a plasmid through post-segregational killing of cells that have lost the plasmid. Key to their function is the tight regulation of expression of a protein toxin by an sRNA antitoxin. Here, we focus on the nonlinear nature of the regulatory circuit dynamics of the toxin-antitoxin mechanism. The mechanism relies on a transient increase in protein concentration rather than on the steady state of the genetic circuit. Through a systematic analysis of the parameter dependence of this transient increase, we confirm some known design features of this system and identify new ones: for an efficient toxin-antitoxin mechanism, the synthesis rate of the toxin's mRNA template should be lower that of the sRNA antitoxin, the mRNA template should be more stable than the sRNA antitoxin, and the mRNA-sRNA complex should be more stable than the sRNA antitoxin. Moreover, a short half-life of the protein toxin is also beneficial to the function of the toxin-antitoxin system. In addition, we study a therapeutic scenario in which a competitor mRNA is introduced to sequester the sRNA antitoxin, causing the toxic protein to be expressed.},
  language  = {en}
}
@article{GhaisariWinklhoferStrauchetal.2017,
  author    = {Ghaisari, Sara and Winklhofer, Michael and Strauch, Peter and Klumpp, Stefan and Faivre, Damien},
  title     = {Magnetosome Organization in Magnetotactic Bacteria Unraveled by Ferromagnetic Resonance Spectroscopy},
  series = {Biophysical journal},
  volume    = {113},
  journal   = {Biophysical journal},
  publisher = {Cell Press},
  address   = {Cambridge},
  issn      = {0006-3495},
  doi       = {10.1016/j.bpj.2017.06.031},
  pages     = {637 -- 644},
  year      = {2017},
  abstract  = {Magnetotactic bacteria form assemblies of magnetic nanoparticles called magnetosomes. These magnetosomes are typically arranged in chains, but other forms of assemblies such as clusters can be observed in some species and genetic mutants. As such, the bacteria have developed as a model for the understanding of how organization of particles can influence the magnetic properties. Here, we use ferromagnetic resonance spectroscopy to measure the magnetic anisotropies in different strains of Magnetosprillum gtyphiswaldense MSR-1, a bacterial species that is amendable to genetic mutations. We combine our experimental results with a model describing the spectra. The model includes chain imperfections and misalignments following a Fisher distribution function, in addition to the intrinsic magnetic properties of the magnetosomes. Therefore, by applying the model to analyze the ferromagnetic resonance data, the distribution of orientations in the bulk sample can be retrieved in addition to the average magnetosome arrangement. In this way, we quantitatively characterize the magnetosome arrangement in both wild-type cells and Delta mamJ mutants, which exhibit differing magnetosome organization.},
  language  = {en}
}
@article{CoduttiBenteFaivreetal.2019,
  author    = {Codutti, Agnese and Bente, Klaas and Faivre, Damien and Klumpp, Stefan},
  title     = {Chemotaxis in external fields: Simulations for active magnetic biological matter},
  series = {PLoS Computational Biology : a new community journal},
  volume    = {15},
  journal   = {PLoS Computational Biology : a new community journal},
  number    = {12},
  publisher = {PLoS},
  address   = {San Fransisco},
  issn      = {1553-734X},
  doi       = {10.1371/journal.pcbi.1007548},
  pages     = {26},
  year      = {2019},
  abstract  = {The movement of microswimmers is often described by active Brownian particle models. Here we introduce a variant of these models with several internal states of the swimmer to describe stochastic strategies for directional swimming such as run and tumble or run and reverse that are used by microorganisms for chemotaxis. The model includes a mechanism to generate a directional bias for chemotaxis and interactions with external fields (e.g., gravity, magnetic field, fluid flow) that impose forces or torques on the swimmer. We show how this modified model can be applied to various scenarios: First, the run and tumble motion of E. coli is used to establish a paradigm for chemotaxis and investigate how it is affected by external forces. Then, we study magneto-aerotaxis in magnetotactic bacteria, which is biased not only by an oxygen gradient towards a preferred concentration, but also by magnetic fields, which exert a torque on an intracellular chain of magnets. We study the competition of magnetic alignment with active reorientation and show that the magnetic orientation can improve chemotaxis and thereby provide an advantage to the bacteria, even at rather large inclination angles of the magnetic field relative to the oxygen gradient, a case reminiscent of what is expected for the bacteria at or close to the equator. The highest gain in chemotactic velocity is obtained for run and tumble with a magnetic field parallel to the gradient, but in general a mechanism for reverse motion is necessary to swim against the magnetic field and a run and reverse strategy is more advantageous in the presence of a magnetic torque. This finding is consistent with observations that the dominant mode of directional changes in magnetotactic bacteria is reversal rather than tumbles. Moreover, it provides guidance for the design of future magnetic biohybrid swimmers. Author summary In this paper, we propose a modified Active Brownian particle model to describe bacterial swimming behavior under the influence of external forces and torques, in particular of a magnetic torque. This type of interaction is particularly important for magnetic biohybrids (i.e. motile bacteria coupled to a synthetic magnetic component) and for magnetotactic bacteria (i.e. bacteria with a natural intracellular magnetic chain), which perform chemotaxis to swim along chemical gradients, but are also directed by an external magnetic field. The model allows us to investigate the benefits and disadvantages of such coupling between two different directionality mechanisms. In particular we show that the magnetic torque can speed chemotaxis up in some conditions, while it can hinder it in other cases. In addition to an understanding of the swimming strategies of naturally magnetotactic organisms, the results may guide the design of future biomedical devices.},
  language  = {en}
}