<i>Acinetobacter baumannii</i> Employs a Rare Fatty Acid Desaturase for Niche-Specific Host Adaptation

<i>Acinetobacter baumannii</i> is a hospital-associated pathogen with unique fatty acid homeostasis features. This includes a reliance on desaturases for proliferation, due to an inability to generate unsaturated fatty acids during the synthesis cycles. However, there are various unexplained gaps in <i>A. baumannii</i> fatty acid homeostasis, such as the desaturation of <i>de novo</i> synthesized fatty acids. We identified a conserved desaturase (DesC) with a rare structural feature that may have roles in coordinating fatty acids with acyl carrier protein conjugants. We showed that DesC can generate fatty acids with <i>cis</i> double bonds in the delta-9 position. Profiling of <i>A. baumannii</i> fatty acids and mRNA transcripts emphasized its significance during fatty acid synthesis. DesC was found to be most critical in mouse niches where <i>A. baumannii</i> relies on fatty acid synthesis. This work has contributed to our understanding of core metabolic features that are key to the disease potential of <i>A. baumannii</i>.