Subcellular compartmentalization of sulfur metabolism in a bacterial pathogen

The National Institute of Allergy and Infectious Diseases awarded Vanderbilt University Medical Center $153,560 on October 10, 2026, under the Allergy and Infectious Diseases Research program (CFDA 93.855) to investigate subcellular compartmentalization of sulfur metabolism in Acinetobacter baumannii, a bacterial pathogen responsible for 15–25 percent of ventilator-associated pneumonia cases in hospitals.

The research examines how A. baumannii regulates sulfur uptake and metabolism during infection, focusing on a conserved four-gene operon that encodes an encapsulin nanocompartment loaded with cysteine desulfurase. The work will test the hypothesis that this encapsulin operon is critical to bacterial infection, upregulated during sulfur starvation, and involved in iron-sulfur cluster repair of client proteins. The recipient will determine the in vivo physiological function and virulence contribution of this structure and extend findings to other bacterial phyla. The research is assistance type Project Grant.

Performance occurs in Forest Hills, Tennessee, with a period of performance from October 10, 2026, through June 30, 2027.

Abstract

Sulfur uptake and metabolism are fundamental processes to all life that must be precisely regulated to maintain proper enzymatic functions, redox potential, and general cellular homeostasis. Bacterial pathogens are no exception to this, as they must acquire and assimilate sulfur during infection to colonize tissue and cause disease. The important pathogen acinetobacter baumannii is responsible for 15-25% of ventilator-associated pneumonia cases in hospitals with isolation of multi- and extensively drug-resistant strains becoming increasingly prevalent. Recent work has identified a conserved four gene operon in a. Baumannii that is upregulated in response to sulfur starvation which encodes for an encapsulin nanocompartment that is loaded with a cysteine desulfurase (ENCCD). In vitro structural studies have found that the activity of encapsulated ENCCD leads to accumulation of sulfur within the encapsulin lumen. However, the physiological function and contribution to virulence of this structure remains unknown. Interestingly, we have found that expression of the a. Baumannii encapsulin operon results in increased resistance to superoxide. Superoxide is a reactive oxygen species that damages essential iron-sulfur (FE-S) cluster cofactors within proteins, suggesting that the CD-encapsulin system is involved in FE-S cluster repair. I hypothesize that the encapsulin operon is critical to a. Baumannii infection and is upregulated by an unknown transcription factor(S) during sulfur starvation. Subsequently, the activity of ENCCD results in a sulfur pool within the encapsulin lumen that is accessed by encrd and utilized for FE-S cluster repair of encrd-client proteins. Experiments in this proposal will test this hypothesis and contribute to the understanding of encapsulins and FE-S cluster repair in a. Baumannii and other bacterial phyla. Additionally, I will determine the in vivo encapsulin ultrastructure using advanced imaging techniques. Results from this study will not only elucidate the function of CD-encapsulin system but may also identify a novel therapeutic target for a. Baumannii infection.