Phenotypic Switching of Bacterial Cells in Extreme Environments

Student: Sudip Nepal

Degree: Ph.D., July 2020

Major Professor: Dr. Pradeep Kumar

Research Area(s):

Biological Materials & Processes

Modeling & Simulation

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  • While there are studies on the cellular response of bacteria under continuous environmental stress, cellular response under temporal fluctuations of environmental stress poorly explored.
  • Biological switches in response to external perturbations allow cells to change to different phenotypes that can withstand environmental stress.


  • Stochastic switching is a survival strategy under environmental stress. This study will explore phenotypic switching of bacteria under extreme environmental fluctuations, such as pressure, salinity, and pH using experimental and theoretical approaches.


  • Fluorescence and phase contrast images of bacteria grown in different environments are acquired and analyzed to characterize different phenotypes.
  • Stochastic switching of the cells at fluctuating pressure is explained using a new model for cell division in conjunction with with 2-state behavior of the cells.
  • Time-lapse movies of the cells are obtained and analyzed to investigate the cell division of a heterogeneous population of phenotypes.

Key Results

  • Bacterial cells exhibit phenotypic switching at high pressure and high salinity, and these phenotypes are reversible upon the removal of the applied stress.
  • Cells exhibit plasmolysis at high MgSO4 concentration, and the plasmolysis is stronger at poles.
  • The genes involved in sulfate transport and osmotic response are upregulated at high concentration of magnesium sulfate.


  • Bacteria switch to a new phenotype at high pressure and salinity that is reversible upon removal of pressure and salt stresses.

  • At high salinity, cells undergo plasmolysis. The gene involved in sulfate transport and an osmotically inducible gene are upregulated at  1.25 M MgSO4.

Future Work

  • Investigate the adaptation of bacteria in stressed conditions at laboratory time scales.