Phenotypic Variability in Bacterial Populations and Population Fitness Dynamics

University Of Pittsburgh, Pittsburgh PA

Investigators

Abstract

Non-genetic phenotypic variation plays an important role in many biological phenomena. It is generated by a variety of physiological mechanisms and maintained by non-genetic inheritance with variable degrees of fidelity. Transitions between phenotypes are influenced by the internal history of the cell and the environment. The environment, on the other hand, can be altered by the population through metabolism and secretion of chemicals. Therefore, phenotypic variability and population fitness must be understood as a triad dynamical problem of cells-population-environment with dynamic interactions between all levels playing equally important roles. This research project will deepen our understanding of how non-genetic inheritance contributes to phenotypic variability in microorganisms and how variability affects the population fitness. This in turn will help better understand the evolution of such traits in living organisms. The PI will study of the dynamics of protein expression and population fitness. Initially, the influence of growth rate and non-genetic inheritance on the dynamics of protein expression controlled by the LacO promoter will be studied. Based on the acquired data here, together with similar data collected by collaborators on the GAL system in yeast, a universal model describing how the dynamics of protein expression contributes to the variability in protein copy-number across a population will be developed. Afterwards, the dynamics of population fitness and its symbiotic interaction with protein expression will be examined. In addition, the influence of different types of environmental stress on the fitness dynamics and protein expression will be assessed using the LacO system as before and a second model system with engineered plasmids expressing antibiotic resistance. The last stage of the project will focus on the dynamic interaction between phenotypic variability and population fitness in spatially inhomogeneous environments, where the environment can alter the phenotype and thus its interaction with the environment and the population fitness. For this purpose, the sensing network of Escherichia coli will be used as a model system, with the ratio of the receptors Tar/Tsr being the phenotype of interest. This study will examine the variation in the ratio of the two proteins, and aim to: (i) measure the effect of growth rate and protein inheritance on the Tar/Tsr distribution, and (ii) study the dynamics of phenotypic variability and population fitness in spatially inhomogeneous environments. The experiments described above will utilize microfluidic and microscopy techniques, and will be coupled to a theoretical component that aims to develop quantitative modeling of the data acquired and provide predictions that can be experimentally verified. The project will integrate research in the interdisciplinary field of biological physics with education to: (i) Include high school teachers and students in research projects in the PI's laboratory and develop instructional material based on their work to be distributed to high schools in the area. Students from under-represented minority groups will be particularly encouraged to participate in this initiative. (ii) Develop biophysics experiments for students' undergraduate laboratories, and (iii) Introduce new instructional material focusing on applications of physics in biology into courses at all levels in the undergraduate program. This project is being jointly supported by the Physics of Living Systems program in the Division of Physics and the Cellular Dynamics and Function Program in the Division of Molecular and Cellular Biosciences.