Disruption of cysteine metabolism leads to synthetic lethality and in vivo fitness impairment in Acinetobacter baumannii

Acinetobacter baumannii is a critical nosocomial pathogen that causes infections in diverse host niches, including the respiratory tract, bloodstream, and urinary tract. Considering the contemporary landscape of antibiotic resistance, alongside targeting resistance determinants, there is a need to identify novel and alternative targets for therapeutic intervention. Central metabolism plays a major role in the success of a pathogen and represents a pool of plausible drug targets. However, metabolic networks are inherently complex and often employ redundant pathways to ensure the supply of essential metabolites. In our efforts to delineate the metabolic pathways contributing to the pathophysiological fitness of A. baumannii , we focused on biosynthesis and uptake mechanisms that maintain intracellular cysteine homeostasis. Cysteine is one of the least abundant amino acids in proteins; however, it is crucial for the folding and catalytic activity of enzymes involved in diverse pathophysiological pathways. We show that A. baumannii possesses two partially redundant serine acetyltransferases involved in cysteine biosynthesis. Disruption of cysteine biosynthesis affects the intracellular cysteine pool, leading to metabolic dysregulation. The metabolic dysregulation further leads to a defect in cellular bioenergetics, oxidative stress mitigation, and antibiotic stress survival in vitro and in vivo . Combinatorial disruption of cysteine biosynthesis and cystine transport results in synthetic lethality and fitness attenuation within the host. Our work provides insights into the metabolic complexities and vulnerabilities of A. baumannii and underscores the therapeutic potential of targeting pathways that sustain cysteine homeostasis, including combination strategies, to combat infections caused by this priority pathogen. IMPORTANCE Acinetobacter baumannii is a critical nosocomial pathogen, and the rising prevalence of antibiotic resistance in this organism necessitates the identification of novel therapeutic targets. Central metabolism, particularly amino acid metabolic pathways, represents a promising yet underexplored area for such interventions. Cysteine, a sulfur-containing amino acid, is essential for the activity of different enzymes involved in key physiological processes. In this study, we demonstrate that the cysteine biosynthesis pathway plays a critical role in maintaining metabolic homeostasis and survival under antibiotic stress while exhibiting functional redundancy with the cystine uptake system in sustaining in vivo fitness in A. baumannii . Simultaneous disruption of cysteine biosynthesis and uptake results in synthetic lethality and a marked fitness defect in a murine pneumonia model. Our work reveals metabolic complexities and highlights the metabolic vulnerabilities of A. baumannii , which can be further explored for therapeutic interventions to curb infections caused by this priority pathogen.