A hybrid sensor kinase regulates acetate metabolism and transport in Acinetobacter baumannii

Abstract Acinetobacter baumannii is a problematic pathogen in hospital settings. This study investigated a multi-component regulatory system involved in acetate metabolism in A. baumannii . Through transcriptomic, bioinformatic, and biophysical analyses, we characterised a hybrid histidine kinase, AcmS, encoded by the ABUW_0182 gene. Our findings suggest AcmS likely operates via a multistep phosphorelay mechanism in conjunction with a response regulator (AcmR) to control the expression of acetate metabolism genes. Biophysical analyses revealed that AcmS binds acetic and propionic acids with low micromolar affinity. Furthermore, inactivation of acmS significantly reduces cellular uptake of radiolabelled acetic acid, and acmS and acmR mutants are defective for growth on acetate, a phenotype restored upon complementation of acmS . Our data indicates AcmS not only activates the expression of genes essential for acetate metabolism, but also directly binds and facilitates the transport of acetic acid, suggesting that acetate is the physiological ligand of this hybrid histidine kinase system.