Seminar über aktuelle Fragen zur Dynamik komplexer Fluide: Swimming with multiple flagella

Seminar über aktuelle Fragen zur Dynamik komplexer Fluide

  • Date: Apr 27, 2018
  • Time: 10:15 AM - 11:15 AM (Local Time Germany)
  • Speaker: Javad Najafi
  • Saarland University, Saarbrücken
  • Location: Max-Planck-Institut für Dynamik und Selbstorganisation (MPIDS)
  • Room: SR 0.77
  • Host: MPIDS/DCF
  • Contact:
Many prokaryotes employ rotating helical appendages known as flagella to propel themselves in aqueous medium. Peritrichous bacteria such as Escherichia coli synchronize and bundle their flagella to actively swim while dispersion of bundle leads to tumbling. Various species have different number of flagella but it is not well understood what the consequences are for them. We studied differentially flagellated Bacillus subtilis strains as model system to shed light on the dynamics of swimming bacteria with multiple flagella.
Decreasing the number of flagella reduces the average turning angle between successive run phases and enhances the run time and directional persistency of the run phase. Consequently, having less flagella is beneficial for long distance transport and fast spreading while having a lot of flagella is advantageous for the processes which require slower spreading such as biofilm formation. We developed a two-state random walk model which yields exact analytical expression for the transport properties in agreement with experiments. The results of numerical simulations based on the two-state model have been used to discuss the search efficiency of different strains. We stained flagella to further investigate the dynamics of bundling, and interestingly found that Bacillus subtilis can make several bundles during run phase where the probability distribution of the number of bundles is similar for all strains independent of the flagellar number. The projected angle between the bundles on the observation plane widens with increasing the number of flagella leading to slight modification of effective cell aspect ratio while the other bundle properties do not significantly change.
Collective motion of dense suspension of bacteria will be also addressed to understand how the dynamics of individual cells and their geometrical properties, i.e., their aspect ratio including flagellar bundle can influence characteristic features of collective behavior. The results show that the characteristic time and length scale of the collective motion are robust to the shape variation and swimming dynamics of the individual cells in the range of experimental parameters.
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