Roles of GacSA and DJ41_1407 in Acinetobacter baumannii ATCC 19606

Two-component systems (TCSs) in bacteria are often involved in the global regulation of various physiological activities and behaviours. This study investigated the GacSA TCS and DJ41_1407 transcriptional sensor adjacent to GacA in <i>Acinetobacter baumannii</i> ATCC 19606. The relationship between GacS, GacA, and DJ41_1407 and their functions and signal transduction mechanisms are described. <i>A. baumannii</i> ATCC 19606 mutants, ∆<i>gacS</i>, ∆<i>gacA</i>, and ∆<i>DJ41_1407</i>, were generated using markerless mutation and cultured in LB medium, then collected for RNA sequencing. It was found that GacS, GacA, and DJ41_1407 regulate a series of genes involved in carbon metabolism. Quantitative reverse transcription PCR (qRT-PCR) results showed that DJ41_1407 and GacA may regulate the expression of <i>adh4</i>, <i>ipdC, iacH</i>, and <i>paa</i>. Phos-tag™ results revealed that GacS plays a more significant role in GacA phosphorylation. GacA regulated colony size and growth conditions in rich medium. Compared to the wild-type strain, the ∆<i>gacA</i> and ∆<i>gacSA</i> mutants exhibited smaller colony sizes, and mutation of the <i>gacS</i>, <i>gacA</i>, and <i>DJ41_1407</i> genes also reduced bacterial virulence as determined by the <i>Galleria mellonella</i> infection assay. GacA also plays a crucial role in modulating antibiotic resistance, and the ∆<i>gacA</i>∆<i>DJ41_1407</i> mutant demonstrated greater susceptibility to antibiotics. These results highlight the multiple functions regulated by the GacSA global TCS in <i>A</i>. <i>baumannii</i> ATCC 19606.