Too Much of a Good Thing? Differential Gene Expression in Escherichia coli Associated with the Evolution of Resistance to Heavy Metals

Student Classification


Faculty Mentor

Misty Thomas, Ph.D. and Scott Harrison, Ph.D.


Department of Biology

Document Type


Publication Date

Fall 2018




DNA sequencing of experimentally evolved iron (II) resistant strains of Escherichia coli (E. coli) K-12 MG1655, identified 21 genes which selectively swept the populations. The goal of this study is to analyze the differential mRNA expression patterns of 50 selected genes (based on gene networks associated with the 21 genes found in DNAseq) using the nanoString technology. For this study, we used three different lines of E.coli K-12 MG1655 with 5 replicates of each all grown in standard DMB media. We used E.coli K-12 MG1655 grown in standard DMB media as our control, an experimentally evolved iron (II) resistant strain, that is maintained in 1750 µg/mL iron (II) sulfate and an experimentally evolved silver resistant strain (Tajkarimi et al. 2017), subsequently evolved to then become iron (II) resistant maintained in presence of 1750 µg/mL iron (II) sulfate. Strains were then grown into lag, log and stationary phase in presence and absence of iron (II) sulfate, RNA was extracted and quantified then sent to nanoString (https://www.nanostring.com) for quantification of gene expression patterns of our 50 selected genes. The differences observed in growth rates of the different strains and under stress of iron sulfate indicated that there is likely a changed in gene expression between the different strain/conditions tested. Overall, the iron resistant strains responded by own regulating the iron regulator protein gene fur and iron transport genes. In addition, the iron resistant strains, in the presence of iron, downregulated genes that play a role in survival and reproduction. This accurately correlates with lower fitness levels shown during the growth of these strains; which may be a method these strains use as a defense until the environment is suitable for growth. This study will provide further information regarding how E. coli can adapt and evolve in presence of heavy metals such iron and silver and understanding these mechanisms before they appear in nature is a proactive approach to addressing an inevitable problem. The limitations in our study are that nanoString technology is cost-effective method and cuts down on data analysis, there is the likely possibility that we are missing out on some key expression findings. Therefore, subsequent to the nanoString experiments we will then analyze the sample samples using RNA-seq in order to get a complete view of all differential expression under our tested conditions.

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