LAUSR

Acinetobacter baumannii is a well-known nosocomial pathogen that can survive in different environments through the use of intricate networks to regulate gene expression. Two-component systems (TCS) form an important part of such regulatory networks, and in this study, we describe the identification and characterization of a novel EmaSR TCS in A. baumannii. We constructed a Tn5-tagged mutagenesis library, from which an emaS sensor kinase gene and emaR response regulator gene were identified. We found that emaS/emaR single-mutants and double-mutants were unable to replicate in M9 medium with 1% ethanol as the single carbon source. Motility and biofilm formation were negatively affected in double-mutants, and transcriptomic analysis showed that mutation of emaSR dysregulated genes required for carbon metabolism. In addition, emaS/emaR single-mutants and double-mutants were unable to survive in acetic acid- and sodium acetate-containing medium, indicating that the EmaSR TCS is also important for acetate metabolism. Furthermore, virulence against Galleria mellonella was diminished in emaS/emaR single- and double-mutants. Taken together, these results show that this novel EmaSR TCS is involved in the regulation of A. baumannii ethanol metabolism and acetate metabolism, with important implications on motility, biofilm formation, and virulence if mutated. Further research on the underlying mechanisms is warranted.