The AdcACB/AdcAII system is essential for zinc homeostasis and an important contributor of Enterococcus faecalis virulence

Abstract

Bacterial pathogens require a variety of micronutrients for growth, including trace metals such as iron, manganese, and zinc (Zn). Despite their relative abundance in host environments, access to these metals is severely restricted during infection due to host-mediated defense mechanisms collectively known as nutritional immunity. Despite a growing appreciation of the importance of Zn in host-pathogen interactions, the mechanisms of Zn homeostasis and the significance of Zn to the pathophysiology of E. faecalis , a major pathogen of nosocomial and community-associated infections, have not been thoroughly investigated. Here, we show that E. faecalis encoded ABC-type transporter AdcACB and an orphan substrate-binding lipoprotein AdcAII that work cooperatively to maintain Zn homeostasis. Simultaneous inactivation of adcA and adcAII or the entire adcACB operon led to a significant reduction in intracellular Zn under Zn-restricted conditions and heightened sensitivity to Zn-chelating agents including human calprotectin, aberrant cell morphology, and impaired fitness in serum ex vivo . Additionally, inactivation of adcACB and adcAII significantly reduced bacterial tolerance toward cell envelope-targeting antibiotics. Finally, we showed that the AdcACB/AdcAII system contributes to E. faecalis virulence in a Galleria mellonella invertebrate infection model and in two catheter-associated mouse infection models that recapitulate many of the host conditions associated with enterococcal human infections. Collectively, this report reveals that high-affinity Zn import is important for the pathogenesis of E. faecalis establishing the surface-associated AdcA and AdcAII lipoproteins as potential therapeutic targets.

Transition metals and Enterococcus faecalis: Homeostasis, virulence and perspectives

“…The ability of E. faecalis to survive in Zn-restricted environment is attributed to its high affinity zinc acquisition system AdcACB (annotated as znuACB) and its orphan substrate-binding lipoprotein AdcAII (Lam et al, 2022). The AdcACB/AdcAII system was induced under Zn starvation, which leads to elevated intracellular zinc levels.…”

“…In this mechanism, a zincophore is exported to bind the extracellular zinc followed by the import of the zincophore-zinc complex (Grim et al, 2017). However, such a mechanism has not been identified in E. faecalis (Lam et al, 2022).…”

“…Contribution of Zn to E. faecalis growth was demonstrated by the sever growth defects observed upon the simultaneous inactivation of the Zn-binding lipoproteins AdcA and AdcII or the ABC-type AdcACB transport family protein, and these defects were partially restored by zinc supplementation (Lam et al, 2022). Zinc supplementation also rescued the inhibited growth of E. faecalis devoid of the ACB protein and/or the orphan lipoprotein AdcII in the presence of zinc chelator (Lam et al, 2022).…”

“…Contribution of Zn to E. faecalis growth was demonstrated by the sever growth defects observed upon the simultaneous inactivation of the Zn-binding lipoproteins AdcA and AdcII or the ABC-type AdcACB transport family protein, and these defects were partially restored by zinc supplementation (Lam et al, 2022). Zinc supplementation also rescued the inhibited growth of E. faecalis devoid of the ACB protein and/or the orphan lipoprotein AdcII in the presence of zinc chelator (Lam et al, 2022). The AdcACB/AdcAII system contributes to E. faecalis survival in zinc depleted-fluids such as serum, tolerance to the metal chelating effects of calprotectin, and cell envelop targeting antibiotics such as ampicillin, bacitracin, and daptomycin (Lam et al, 2022).…”

“…The understanding of how transition metals influence E. faecalis virulence, alter its transcriptome, and how this pathogen regulates metal homeostasis has advanced significantly over the past few years (Abrantes et al, 2014;Colomer-Winter et al, 2018;Keogh et al, 2018;Lam et al, 2022;Low et al, 2003). Meanwhile, the role of transition metals and their homeostasis mechanisms in several bacterial pathogens has been reviewed (Porcheron et al, 2013).…”