Correlation between protein concentration and bacterial cell size can reveal mechanisms of gene expression

• Published in: Physical biology Vol. 17; no. 4; p. 045002
• Main Authors: Nieto-Acuña, César, Arias-Castro, Juan Carlos, Vargas-García, César, Sánchez, Carlos, Pedraza, Juan Manuel
• Format: Journal Article
• Language: English
• Published: England IOP Publishing 01.07.2020
• Subjects: cell size; division; Escherichia coli - cytology; Escherichia coli - genetics; Escherichia coli Proteins - analysis; Escherichia coli Proteins - genetics; gene expression; Gene Expression Regulation, Bacterial; Plasmids - genetics
• ISSN: 1478-3975; 1478-3967; 1478-3975
• DOI: 10.1088/1478-3975/ab891c

Classically, gene expression is modeled as a chemical process with reaction rates dependent on the concentration of the reactants (typically, DNA loci, plasmids, RNA, enzymes, etc). Other variables like cell size are in general ignored. Size dynamics can become an important variable due to the low number of many of these reactants, imperfectly symmetric cell partitioning and molecule segregation. In this work we measure the correlation between size and protein concentration by observing the gene expression of the RpOD gene from a low-copy plasmid in Escherichia coli during balanced growth in different media. A positive correlation was found, and we used it to examine possible models of cell size dynamics and plasmid replication. We implemented a previously developed model describing the full gene expression process including transcription, translation, loci replication, cell division and molecule segregation. By comparing with the observed correlation, we determine that the transcription rate must be proportional to the size times the number of plasmids. We discuss how fluctuations in plasmid segregation, due to the low copy number, can impose limits in this correlation.