title: Altered motility of Caulobacter Crescentus in viscous and viscoelastic media.
abstract: BACKGROUND
  Motility of flagellated bacteria depends crucially on their organelles such as flagella and pili, as well as physical properties of the external medium, such as viscosity and matrix elasticity. We studied the motility of wild-type and two mutant strains of Caulobacter crescentus swarmer cells in two different types of media: a viscous and hyperosmotic glycerol-growth medium mixture and a viscoelastic growth medium, containing polyethylene glycol or polyethylene oxide of different defined sizes.
  
  
  RESULTS
  For all three strains in the medium containing glycerol, we found linear drops in percentage of motile cells and decreases in speed of those that remained motile to be inversely proportional to viscosity. The majority of immobilized cells lost viability, evidenced by their membrane leakage. In the viscoelastic media, we found less loss of motility and attenuated decrease of swimming speed at shear viscosity values comparable to the viscous medium. In both types of media, we found more severe loss in percentage of motile cells of wild-type than the mutants without pili, indicating that the interference of pili with flagellated motility is aggravated by increased viscosity. However, we found no difference in swimming speed among all three strains under all test conditions for the cells that remained motile. Finally, the viscoelastic medium caused no significant change in intervals between flagellar motor switches unless the motor stalled.
  
  
  CONCLUSIONS
  Hyperosmotic effect causes loss of motility and cell death. Addition of polymers into the cell medium also causes loss of motility due to increased shear viscosity, but the majority of immobilized bacteria remain viable. Both viscous and viscoelastic media alter the motility of flagellated bacteria without affecting the internal regulation of their motor switching behavior.
authors.affiliation: Physics Department, Brown University, Providence, RI, 02192, USA. yukun_gao@alumni.brown.edu.
authors.forename: Yukun
authors.initials: Y
authors.lastname: Gao
authors.affiliation: Physics Department, Brown University, Providence, RI, 02192, USA. marianna.h.neubauer@gmail.com.
authors.forename: Marianna
authors.initials: M
authors.lastname: Neubauer
authors.affiliation: Physics Department, Brown University, Providence, RI, 02192, USA. alexander_yang@brown.edu.
authors.forename: Alexander
authors.initials: A
authors.lastname: Yang
authors.affiliation: Physics Department, Brown University, Providence, RI, 02192, USA. nathan_johnson@brown.edu.
authors.forename: Nathan
authors.initials: N
authors.lastname: Johnson
authors.affiliation: Physics Department, Brown University, Providence, RI, 02192, USA. TheMikeMorse@gmail.com.
authors.forename: Michael
authors.initials: M
authors.lastname: Morse
authors.affiliation: Physics Department, Brown University, Providence, RI, 02192, USA. liguanglai@gmail.com.
authors.forename: Guanglai
authors.initials: G
authors.lastname: Li
authors.affiliation: Physics Department, Brown University, Providence, RI, 02192, USA. Jay_Tang@brown.edu.
authors.forename: Jay X
authors.initials: JX
authors.lastname: Tang
mesh_terms: D016935:Caulobacter crescentus / Q000502:physiology*; D003470:Culture Media / Q000737:chemistry*; D004548:Elasticity; D008124:Locomotion; D050296:Microbial Viability; D009997:Osmotic Pressure; D014783:Viscosity
chemical_list: D003470:Culture Media