title: The interrelationship between promoter strength, gene expression, and growth rate.
abstract: In exponentially growing bacteria, expression of heterologous protein impedes cellular growth rates. Quantitative understanding of the relationship between expression and growth rate will advance our ability to forward engineer bacteria, important for metabolic engineering and synthetic biology applications. Recently, a work described a scaling model based on optimal allocation of ribosomes for protein translation. This model quantitatively predicts a linear relationship between microbial growth rate and heterologous protein expression with no free parameters. With the aim of validating this model, we have rigorously quantified the fitness cost of gene expression by using a library of synthetic constitutive promoters to drive expression of two separate proteins (eGFP and amiE) in E. coli in different strains and growth media. In all cases, we demonstrate that the fitness cost is consistent with the previous findings. We expand upon the previous theory by introducing a simple promoter activity model to quantitatively predict how basal promoter strength relates to growth rate and protein expression. We then estimate the amount of protein expression needed to support high flux through a heterologous metabolic pathway and predict the sizable fitness cost associated with enzyme production. This work has broad implications across applied biological sciences because it allows for prediction of the interplay between promoter strength, protein expression, and the resulting cost to microbial growth rates.
authors.affiliation: Department of Chemical Engineering and Materials Science, Michigan State University, East Lansing, Michigan, United States of America.
authors.forename: Matthew S
authors.initials: MS
authors.lastname: Bienick
authors.affiliation: Department of Chemical Engineering and Materials Science, Michigan State University, East Lansing, Michigan, United States of America; High School Honors Science/Mathematics/Engineering Program, Michigan State University, East Lansing, Michigan, United States of America.
authors.forename: Katherine W
authors.initials: KW
authors.lastname: Young
authors.affiliation: Department of Biochemistry and Molecular Biology, Michigan State University, East Lansing, Michigan, United States of America.
authors.forename: Justin R
authors.initials: JR
authors.lastname: Klesmith
authors.affiliation: Department of Chemical Engineering and Materials Science, Michigan State University, East Lansing, Michigan, United States of America.
authors.forename: Emily E
authors.initials: EE
authors.lastname: Detwiler
authors.affiliation: Department of Chemical Engineering and Materials Science, Michigan State University, East Lansing, Michigan, United States of America.
authors.forename: Kyle J
authors.initials: KJ
authors.lastname: Tomek
authors.affiliation: Department of Chemical Engineering and Materials Science, Michigan State University, East Lansing, Michigan, United States of America; Department of Biosystems and Agricultural Engineering, Michigan State University, East Lansing, Michigan, United States of America.
authors.forename: Timothy A
authors.initials: TA
authors.lastname: Whitehead
mesh_terms: D000581:Amidohydrolases / Q000378:metabolism; D004926:Escherichia coli / Q000235:genetics* / Q000254:growth & development; D029968:Escherichia coli Proteins / Q000378:metabolism; D015964:Gene Expression Regulation, Bacterial; D049452:Green Fluorescent Proteins / Q000378:metabolism; D060847:Metabolic Engineering; D008957:Models, Genetic; D011401:Promoter Regions, Genetic; D015203:Reproducibility of Results; D012270:Ribosomes / Q000378:metabolism
chemical_list: D029968:Escherichia coli Proteins; C485184:enhanced green fluorescent protein; D049452:Green Fluorescent Proteins; D000581:Amidohydrolases; C019665:amidase