Differential roles for ArcA and ArcB homologues in swarming motility in Serratia marcescens FS14

ArcAB is a two-component regulatory system that can help bacteria respond to and survive in a changing environment. To identify the function of ArcAB homologues in Serratia marcescens FS14, in-frame deletion mutants of the arcA, arcB and arcAB genes were constructed. Surprisingly, ArcB affects the motility of FS14, but ArcA does not. These results are the reverse of those found in Escherichia coli. Further studies demonstrated that ArcB could promote bacterial motility by activating the synthesis of flagella and particularly by activating the expression of the biosurfactant serrawettin W1. Our results suggest that ArcB may regulate FS14 motility by interacting with an unidentified response regulator other than ArcA. The regulation of ArcAB may be bacterial strain-specific, and the same regulatory system may participate in different mechanisms to adapt to different environments.