Partially Reciprocal Replacement of FlrA and FlrC in Regulation of Shewanella oneidensis Flagellar Biosynthesis

Abstract

In some bacteria with a polar flagellum, an established regulatory hierarchy controlling stepwise assembly of the organelle consists of four regulators: FlrA, σ, FlrBC, and σ Because all of these regulators mediate the expression of multiple targets, they are essential to the assembly of a functional flagellum and therefore to motility. However, this is not the case for the gammaproteobacterium : cells lacking FlrB, FlrC, or both remain flagellated and motile. In this study, we unravel the underlying mechanism, showing that FlrA and FlrC are partially substitutable for each other in regulating flagellar assembly. While both regulators are bacterial enhancer binding proteins (bEBPs) for σ, FlrA differs from FlrC in its independence of σ for its own transcription and its inability to activate the flagellin gene These differences largely account for the distinct phenotypes resulting from the loss or overproduction of FlrA and FlrC. The assembly of a polar flagellum in bacteria has been characterized as relying on four regulators, FlrA, σ, FlrBC, and σ, in a hierarchical manner. They all are essential to the process and therefore to motility, except in , in which FlrB, FlrC, or both together are not essential. Here we show that FlrA and FlrC, as bEBPs, are partially reciprocal in functionality in this species. As a consequence, the presence of one allows flagellar assembly and motility in the other's absence. Despite this, there are significant differences in the physiological roles played by these two regulators: FlrA is the master regulator of flagellar assembly, whereas FlrC fine-tunes motility. These intriguing observations open up a new avenue to further exploration of the regulation of flagellar assembly.

Transcriptional organization and regulation of thePseudomonas putidaflagellar system

“…FlrC, the FleR ortholog of S. oneidensis, is not required for motility and plays a minor role in the regulation of the flagellar promoters (Shi et al, 2014). In this organism ectopic production of FlrC can suppress the nonmotile phenotype of a ∆flrA mutant (lacking the cognate FleQ ortholog) by replacing FlrA as the activator of the flagellar s 54 -dependent promoters (Gao et al, 2018).…”

“…FlrC, the FleR ortholog of S. oneidensis, is not required for motility and plays a minor role in the regulation of the flagellar promoters (Shi et al, 2014). In this organism ectopic production of FlrC can suppress the nonmotile phenotype of a ∆flrA mutant (lacking the cognate FleQ ortholog) by replacing FlrA as the activator of the flagellar s 54 -dependent promoters (Gao et al, 2018). In a similar vein, the functions of FlrA and FlrC are partially redundant in the flagellar cascade of V. campbelli; however, in this case, it is FlrA, and not FlrC, that is dispensable for flagellar motility (Petersen et al, 2021).…”

Role of RpoS in stress resistance, biofilm formation and quorum sensing of Shewanella baltica

“…The primers were designed based on S. baltica OS678 genome in NCBI database (NC_016901.1). The rpoS mutant of S. baltica X7 was constructed according to attbased fusion PCR as described by Gao et al (2018). Briefly, two fragments flanking the upstream and downstream regions of rpoS gene were amplified.…”

Sensor I Regulated ATPase Activity of FleQ Is Essential for Motility to Biofilm Transition in Pseudomonas aeruginosa

“…Deletion of fleQ results in downregulation of flagellar gene expression and renders the bacterium nonmotile . Homologues of FleQ are also present in other monoflagellate bacteria such as Vibrio cholerae , Xanthomonas oryzae , Aeromonas hydrophila , Shewanella oneidensis , and Legionella species. − Structurally, FleQ consists of an N-terminal domain followed by a central AAA+ ATPase domain and the C-terminal DNA binding domain that recognizes a consensus motif. , The central domain harbors the conserved σ 54 interacting motif, the Walker A motif, the Walker B motif, sensor I, and the R-motif. , Interestingly, an antiactivator protein FleN binds with FleQ in an ATP-dependent dimeric form and inhibits its ATPase activity. , …”