Genetic Reporter Systems for Understanding the MAR operon in Escherichia Coli

Over the past decade, there has been an increasing amount of interest in bacterial individuality arising in clonal populations¹. This emergent behavior often arises from stochasticity at the transcriptional level and is modulated by elements of the greater genetic network². I seek to understand the role that interlocking negative and positive feedback loops within the resistance regulons of Escherichia Coli serve to maximize population fitness while maintaining phenotypic heterogeneity in individuals. To do this, I have developed a series of plasmid-based dynamic reporter systems to measure the expression of marA and downstream genes in real time.  It is important to note that the dynamics of the genes must be normalized to basal fluctuations in total transcription – so-called extrinsic noise. Therefore these reporter systems have the capacity to filter out unwanted variation through cross-correlative analysis with consistently induced genes such as sigma factors.

This platform allows us to gather quantitative data on the pulsing of various proteins as a result of transcriptional stochasticity and genetic network architecture. By combining the reporter systems with iterative deletions in the surrounding genetic architecture, we can further our understanding of how each component gene contributes to emergent phenomena in genetic networks.

1.     Davidson, C. J. & Surette, M. G. Individuality in Bacteria. http://dx.doi.org/10.1146/annurev.genet.42.110807.091601 (2008). doi:10.1146/annurev.genet.42.110807.091601

2.     Sanchez, A. & Golding, I. Genetic Determinants and Cellular Constraints in Noisy Gene Expression. Science 342, 1188–1193 (2013).