The interplay between <i>Acinetobacter baumannii</i> ZigA and SltB promotes zinc homeostasis and cell envelope integrity

<i>Acinetobacter baumannii</i> is an opportunistic human pathogen that acquires nutrient metals from the vertebrate host amid infection. During zinc (Zn) scarcity, <i>A. baumannii</i> upregulates the expression of the predicted Zn metallochaperone, <i>zigA</i>. Loss of <i>zigA</i> compromises fitness during Zn deficiency, highlighting its role in this condition. To assess the contribution of ZigA to Zn-deficient <i>A. baumannii</i>, a multiparallel transposon sequencing and genetic interaction mapping approach was used. Transposon insertions in <i>A1S_3027</i>, encoding a predicted soluble lytic transglycosylase that tailors the bacterial cell wall, were enriched in the Zn-starved Δ<i>zigA</i> transposon library. Based on previous studies as well as structural and sequence homology, we designated A1S_3027 as <u>s</u>oluble <u>l</u>ytic <u>t</u>ransglycosylase <u>B</u> (SltB). Further analyses revealed that inactivating <i>sltB</i> rescued Δ<i>zigA</i> fitness defects during Zn starvation. An <i>A. baumannii</i> Δ<i>zigA</i>Δ<i>sltB</i> mutant demonstrated altered cell envelope structures and increased cellular permeability, highlighting the roles of ZigA and SltB in maintaining cell envelope integrity. Furthermore, these mutants exhibited heightened resistance to β-lactam antibiotics and other cell wall-targeting agents. Alterations in cell envelope integrity in the Δ<i>zigA</i>Δ<i>sltB</i> mutant improved fitness in a murine pneumonia infection model, emphasizing the contribution of ZigA and SltB to <i>A. baumannii</i> pathogenesis. This study elucidates how functional interactions between ZigA and SltB modulate cell envelope integrity and pathogenesis of <i>A. baumannii</i> during Zn depletion. These findings reveal an interplay between metal homeostasis and cell envelope integrity, offering insights into how <i>A. baumannii</i> ZigA contributes to these critical cellular processes.