Abstract
Salmonella enterica is the most frequently reported cause of foodborne illness. As in other microorganisms, chemotaxis affords key physiological benefits, including enhanced access to growth substrates, but also plays an important role in infection and disease. Chemoreceptor signaling core complexes, consisting of CheA, CheW and methyl-accepting chemotaxis proteins (MCPs), modulate the switching of bacterial flagella rotation that drives cell motility. These complexes, through the formation of heterohexameric rings composed of CheA and CheW, form large clusters at the cell poles. RecA plays a key role in polar cluster formation, impairing the assembly when the SOS response is activated. In this study, we determined that RecA protein interacts with both CheW and CheA. The binding of these proteins to RecA is needed for wild-type polar cluster formation. In silico models showed that one RecA molecule, attached to one signaling unit, fits within a CheA-CheW ring without interfering with the complex formation or array assembly. Activation of the SOS response is followed by an increase in RecA, which rises up the number of signaling complexes associated with this protein. This suggests the presence of allosteric inhibition in the CheA-CheW interaction and thus of heterohexameric ring formation, impairing the array assembly. STED imaging demonstrated that all core unit components (CheA, CheW, and MPCs) have the same subcellular location as RecA. Activation of the SOS response promotes the RecA distribution along the cell instead of being at the cell poles. CheA- and CheW- RecA interactions are also crucial for chemotaxis, which is maintained when the SOS response is induced and the signaling units are dispersed. Our results provide new molecular-level insights into the function of RecA in chemoreceptor clustering and chemotaxis determining that the impaired chemoreceptor clustering not only inhibits swarming but also modulates chemotaxis in SOS-induced cells, thereby modifying bacterial motility in the presence of DNA-damaging compounds, such as antibiotics.
Highlights
Chemotaxis allows bacteria to sense their environment and adjust their flagellar rotation resulting in their directed movement toward attractants and away from repellents (Falke et al, 1997; Bi and Lai, 2015)
Neither polar cluster array formation nor chemotaxis (Figures 6, 8) were restored in a recA strain complemented with recA mutant derivatives unable to interact with CheA, CheW or both
Our results provide strong evidence supporting the interaction of RecA with P5-CheA domain (Figure 1), which is structurally similar to CheW (Vu et al, 2012; Table 1)
Summary
Chemotaxis allows bacteria to sense their environment and adjust their flagellar rotation resulting in their directed movement toward attractants and away from repellents (Falke et al, 1997; Bi and Lai, 2015). In many Bacteria and Archaea, MCPs group together to form large chemosensory arrays that contain from a few to thousands of chemoreceptor core complexes (Briegel et al, 2009, 2012, 2015; Greenfield et al, 2009). These ordered structures act as “antennae,” amplifying chemoeffector sensing by cooperative networking (Li and Hazelbauer, 2014; Frank et al, 2016; Piñas et al, 2016). Chemoreceptor clusters are essential for swarming motility (Cardozo et al, 2010; Santos et al, 2014; Irazoki et al, 2016b) and are involved in other important processes, including biofilm formation (He and Bauer, 2014; Huang et al, 2019b), cell adhesion (Huang et al, 2017), host colonization (Erhardt, 2016; Johnson and Ottemann, 2018) and antibiotic resistance (Butler et al, 2010; Irazoki et al, 2017)
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