title: Gene expression analysis of E. coli strains provides insights into the role of gene regulation in diversification.
abstract: Escherichia coli spans a genetic continuum from enteric strains to several phylogenetically distinct, atypical lineages that are rare in humans, but more common in extra-intestinal environments. To investigate the link between gene regulation, phylogeny and diversification in this species, we analyzed global gene expression profiles of four strains representing distinct evolutionary lineages, including a well-studied laboratory strain, a typical commensal (enteric) strain and two environmental strains. RNA-Seq was employed to compare the whole transcriptomes of strains grown under batch, chemostat and starvation conditions. Highly differentially expressed genes showed a significantly lower nucleotide sequence identity compared with other genes, indicating that gene regulation and coding sequence conservation are directly connected. Overall, distances between the strains based on gene expression profiles were largely dependent on the culture condition and did not reflect phylogenetic relatedness. Expression differences of commonly shared genes (all four strains) and E. coli core genes were consistently smaller between strains characterized by more similar primary habitats. For instance, environmental strains exhibited increased expression of stress defense genes under carbon-limited growth and entered a more pronounced survival-like phenotype during starvation compared with other strains, which stayed more alert for substrate scavenging and catabolism during no-growth conditions. Since those environmental strains show similar genetic distance to each other and to the other two strains, these findings cannot be simply attributed to genetic relatedness but suggest physiological adaptations. Our study provides new insights into ecologically relevant gene-expression and underscores the role of (differential) gene regulation for the diversification of the model bacterial species.
authors.affiliation: Center for Microbial Ecology, Michigan State University, East Lansing, MI, USA.
authors.forename: Marius
authors.initials: M
authors.lastname: Vital
authors.affiliation: Center for Microbial Ecology, Michigan State University, East Lansing, MI, USA.
authors.forename: Benli
authors.initials: B
authors.lastname: Chai
authors.affiliation: BEACON Center for the Study of Evolution in Action, Michigan State University, East Lansing, MI, USA.
authors.forename: Bjørn
authors.initials: B
authors.lastname: Østman
authors.affiliation: Center for Microbial Ecology, Michigan State University, East Lansing, MI, USA.
authors.forename: James
authors.initials: J
authors.lastname: Cole
authors.affiliation: School of Civil and Environmental Engineering and School of Biology, Georgia Institute of Technology, Atlanta, GA, USA.
authors.forename: Konstantinos T
authors.initials: KT
authors.lastname: Konstantinidis
authors.affiliation: Center for Microbial Ecology, Michigan State University, East Lansing, MI, USA.
authors.forename: James M
authors.initials: JM
authors.lastname: Tiedje
mesh_terms: D004777:Environment; D004926:Escherichia coli / Q000235:genetics*; D029968:Escherichia coli Proteins / Q000235:genetics; D020869:Gene Expression Profiling; D015964:Gene Expression Regulation, Bacterial; D016680:Genome, Bacterial; D006801:Humans; D007422:Intestines / Q000382:microbiology; D010802:Phylogeny; D017423:Sequence Analysis, RNA; D059467:Transcriptome
chemical_list: D029968:Escherichia coli Proteins