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Differential gene expression of three mastitis-causing Escherichia coli strains grown in planktonic, swimming, and swarming culture conditions

John D. Lippolis, Brian W. Brunelle, Timothy A. Reinhardt, Randy E. Sacco, Tyler C. Thacker, Torey P. Looft, Thomas A. Casey
mSystems 2016 v.1 no.4 pp. -
Escherichia coli, bacteria, bacterial motility, chelation, chronic diseases, culture media, dairy cattle, gene expression, gene expression regulation, genes, iron, phenotype, sequence analysis, swimming, transcriptome, transcriptomics, virulence
Escherichia coli is a leading cause of intramammary infections in dairy cattle and is typically transient in nature. However, in a minority of cases, E. coli can cause persistent infections. Although the mechanisms that allow for a persistent intramammary E. coli infection are not fully understood, we have previously shown that proficient bacterial motility (swimming and swarming) in vitro is correlated with the persistent infection phenotype observed in cattle. In this work, three E. coli strains that cause persistent infections were grown in liquid culture media (planktonic), as well as on semi-solid media that promote swimming and swarming motility phenotypes. Using whole transcriptome RNA sequencing, we identified genes that were differentially expressed among these three growth conditions. We contend that better understanding of the genes that are differentially expressed due to the type of motility will yield important information about how bacteria can establish a persistent infection. Our data indicate that iron plays a critical role in motility, as genes associated with iron account for nearly 7% of all the genes that are differentially regulated. The addition of iron to the motility-promoting media has a negative effect on swarming and no effect on swimming, while the chelation of iron causes changes in the swimming pattern but little effect on swarming. Critically, bacterial motility is thought to play an important role in virulence. Elucidating the mechanisms that regulate bacterial motility and its relationship to persistent intramammary infections may provide new approaches in the development of intervention strategies, as well as facilitate the discovery of novel diagnostics and therapeutics. Unique to this report is the complete transcriptomics comparison of gene expression differences between growth in liquid LB, swimming plates, and swarming plates of three strains of E. coli.