In silico metabolic profiling of non-baumannii Acinetobacter species uncovers conserved functions and provides first evidence of siderophore biosynthetic genes in Acinetobacter junii

Abstract

The genus Acinetobacter is recognized for its metabolic versatility, which contributes to environmental persistence, virulence, and antimicrobial resistance. This study aimed to elucidate the metabolic pathways, particularly those associated with virulence and antimicrobial resistance (AMR), in non-baumannii Acinetobacter species. Genome-scale metabolic prediction of 19 Acinetobacter isolates identified 104 distinct pathways spanning 32 metabolic categories. Ninety-six pathways were conserved across all genomes, whereas a small subset exhibited species- or strain-specific distributions: four pathways occurred in 18 isolates, three were restricted to five A. junii isolates, and one was unique to 14 A. nosocomialis genomes. Amino acid metabolism was the most diverse (29 pathways), followed by lipid metabolism (14 pathways) and energy metabolism (8 pathways). The 96 conserved pathways supported essential cellular functions, including protein synthesis, energy production, and nucleotide metabolism. Notably, 20 pathways were associated with virulence, pathogenicity, and AMR, spanning lipid metabolism, siderophore biosynthesis, and nucleotide metabolism, among others. Eighteen of these pathways were conserved across all isolates and encompassed diverse metabolic functions, including protein N-glycosylation, heme biosynthesis, lipid IVA synthesis, fatty acid β-oxidation, tRNA maturation, triclosan resistance, and superoxide degradation. Interestingly, all A. junii isolates uniquely encoded siderophore biosynthesis systems. In silico analysis of the whole-genome sequences from the five A. junii isolates revealed the presence of genes sharing > 91% sequence identity with the acinetoferrin biosynthetic cluster (acbABCD) from Acinetobacter haemolyticus. Additionally, genes homologous to the acinetoferrin transport genes (actB, actC, actA, and actD) were identified. However, genes associated with the desferrioxamine E biosynthetic pathway were not detected in these isolates. The high degree of conservation of the acinetoferrin biosynthetic cluster in A. haemolyticus and A. junii suggests that A. junii likely produces acinetoferrin. These findings highlight the high degree of conservation of metabolic pathways in non-baumannii Acinetobacter species and represent the first report of the putative acinetoferrin biosynthetic gene cluster in A. junii.