FliL has a conserved function in diverse microbes to negatively modulate motor output via its N-terminal region

Abstract

Bacterial surface sensing is often conferred by flagella. The flagellar motor protein FliL plays a key role in this process, but its exact role has been obscured by varying fliL mutant phenotypes. We reanalyzed results from studies on these fliL alleles and found they inadvertently compared mutants with differing length of the retained native N-terminal region, including the transmembrane helix (TM). We find that TM retention in the mutants that lack the native C-terminal domain results in loss of swimming and swarming motility, while alleles that completely lack the TM retain motility. We suggest FliL negatively regulates motor function via its N-terminal region, an observation that may relate to FliL function in mechanosensing.