Differential Gene Expression of Three Mastitis-causing Escherichia coli Strains Grown in Planktonic, Swimming, and Swarming Culture Conditions

Bacterial motility is thought to play an important role in virulence. We have previously shown that proficient bacterial swimming and swarming in vitro is correlated with the persistent intramammary infection phenotype observed in cattle. However, little is known about the gene regulation differences important for different motility phenotypes in E. coli. In this work, three E. coli strains that cause persistent bovine mastitis infections were grown in three mediums that promote different types of motility (planktonic, swimming, and swarming). Using whole transcriptome RNA sequencing, we identified a total of 935 genes (~21% of the total genome) that were differentially expressed between the various motility promoting conditions. We found that approximately 7% of the differentially expressed genes were associated with iron regulation. We show that motility assays using iron or iron chelators confirmed the importance of iron regulation to the observed motility phenotypes. Because of the observation that E. coli strains that cause persistent infections are more motile, 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 become established within a host. Elucidating the mechanisms that regulate bacterial motility may provide new approaches in the development of intervention strategies, as well as facilitate the discovery of novel diagnostics and therapeutics.