Role of Motility and the flhDC Operon in Escherichia coli MG1655 Colonization of the Mouse Intestine

Abstract

Previously, we reported that the mouse intestine selected mutants of Escherichia coli MG1655 that have improved colonizing ability (M. P. Leatham et al., Infect. Immun. 73:8039-8049, 2005). These mutants grew 10 to 20% faster than their parent in mouse cecal mucus in vitro and 15 to 30% faster on several sugars found in the mouse intestine. The mutants were nonmotile and had deletions of various lengths beginning immediately downstream of an IS1 element located within the regulatory region of the flhDC operon, which encodes the master regulator of flagellum biosynthesis, FlhD 4 C 2 . Here we show that during intestinal colonization by wild-type E. coli strain MG1655, 45 to 50% of the cells became nonmotile by day 3 after feeding of the strain to mice and between 80 and 90% of the cells were nonmotile by day 15 after feeding. Ten nonmotile mutants isolated from mice were sequenced, and all were found to have flhDC deletions of various lengths. Despite this strong selection, 10 to 20% of the E. coli MG1655 cells remained motile over a 15-day period, suggesting that there is an as-yet-undefined intestinal niche in which motility is an advantage. The deletions appear to be selected in the intestine for two reasons. First, genes unrelated to motility that are normally either directly or indirectly repressed by FlhD 4 C 2 but can contribute to maximum colonizing ability are released from repression. Second, energy normally used to synthesize flagella and turn the flagellar motor is redirected to growth.Intestinal colonization is defined as the indefinite persistence of a bacterial population in the intestine of an animal in stable numbers without repeated introduction of the bacterium into the animal. Commensal Escherichia coli strains colonize the mouse intestine by growing in the intestinal mucus layer which covers the epithelium (18,24,25,28,38,39,43). The intestinal mucus layer is constantly being synthesized, degraded by indigenous bacteria, and sloughed into feces (15,27). Colonization requires bacteria to penetrate the mucus layer, compete for nutrients with the indigenous flora, and divide at a rate that is at least equal to the washout rate caused by sloughing of the mucus layer into feces (7, 16); however, the role of motility in mucosal colonization is complex and appears to differ in different microorganisms (12).Motility and chemotaxis in E. coli are controlled by a master regulator encoded by flhD and flhC, which comprise the flhDC operon. Together, FlhD and FlhC form the FlhD 4 C 2 complex (20, 44), which activates transcription of class II flagellar genes that encode components of the flagellar basal body and export machinery (30). One of the class II flagellar genes, fliA, encodes an RNA polymerase sigma factor, 28 , which switches on expression of the class III genes coding for the cell-distal structural components of the flagellum (30). The sequenced E. coli MG1655 strain has an IS1 element in the regulatory region of the flhDC promoter (3), which increases the expression of the flhDC operon and mak...

IS5 inserts upstream of the master motility operon flhDC in a quasi-Lamarckian way

“…The specific growth rate of the cells with IS5 in flhD was slightly lower, and the cells had a lower yield (6 ± 1% reduction) (Figure 2c). This result is consistent with an earlier study, which shows that MG1655 (IS1 inserted upstream of flhDC) grew more slowly than MG1655 that lacks IS1 upstream of flhDC due to the reduction in energy available for growth due to the enhanced motility (Gauger et al, 2007). For our work, when IS5 was cured from the upstream region of flhD þ , growth, motility and biofilm formation were restored to the wild-type values (Figure 2), which demonstrates that the increase in motility, the increase in early biofilm formation, and the decrease in growth are due to the presence of IS5 in promoter of flhDC.…”

“…This occurrence of a motile sub-population of cells was also reported for MG1655 fnr from an inoculum of poorly motile MG1655 fnr on soft-agar plates, and PCR screening confirmed that IS5 inserted into the flhDC regulatory region in the same manner (Barker et al, 2004). The sequenced K12 strain, MG1655, is a relative of BW25113 (Baba et al, 2006), and is highly motile because of a similar IS1 insertion sequence upstream of flhD þ (Blattner et al, 1997;Gauger et al, 2007).…”

“…In recent years, insertion elements IS1 and IS5 have been identified in some E. coli strains that activate the promoter of flhDC and increase motility (Barker et al, 2004;Gauger et al, 2007); however, these mutations were rejected as cases of directed mutation (Barker et al, 2004). Here, we explored the regulation of flhDC by IS5 hopping under different environmental conditions and found that the environment influences the IS5 insertion upstream of flhDC.…”

Pathogenicity-Associated Islands in Extraintestinal PathogenicEscherichia coliAre Fitness Elements Involved in Intestinal Colonization

“…Motility is a major trait involved in both the pathogen and commensal lifestyles of E. coli (16,34). Different orthologous genes present on several PAIs of E. coli 536 were shown to be involved in the regulation of motility in other ExPEC strains (57,58).…”

Osmotaxis in Escherichia coli through changes in motor speed

“…We discuss how such observed speed increases can lead to negative taxis previously reported. Our study emphasizes the importance of investigating bacterial motility in environments that mimic natural habitats, in the effort to understand the role and evolutionary advantage swimming offers to bacterial cells [Lackraj et al, 2016, Gauger et al, 2007, Tamar et al, 2016.…”