A novel ECF-type transporter promotes heme acquisition in Staphylococcus lugdunensis to overcome nutritional limitation

• Applicant: Professor Dr. Simon Heilbronner
• Subject Area: Medical Microbiology and Mycology, Hygiene, Molecular Infection Biology ; Metabolism, Biochemistry and Genetics of Microorganisms
• Term: from 2019 to 2024
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 429484415

• Final Report Year: 2024

Final Report Abstract

Bacterial pathogens can cause severe and often deadly infections in humans. New strategies to prevent or treat these infections are urgently needed, which requires an in-depth understanding of the molecular mechanisms underlying pathogen biology. During infection, bacteria encounter a hostile environment created by host immune factors aimed at eradicating them. However, successful pathogens manage not only to survive but also to proliferate in such conditions. One strategy the immune system uses to limit pathogen growth is the active reduction of free iron ions. Iron is an essential trace element, and without adequate access to it, pathogens cannot establish infection. To overcome this iron scarcity, some pathogens have developed mechanisms to exploit the host’s hemoglobin pool. Hemoglobin, an abundant protein in humans and contains four heme groups, each with a central iron ion. In this project, we investigate a novel heme acquisition system (LhaSTA) in the bacterial pathogen Staphylococcus lugdunensis. Unlike other known heme acquisition systems, LhaSTA is a member of the Energy-Coupling Factor (ECF) transporter family. ECF transporters are unusual in that they are fully embedded within the bacterial membrane and exhibit very high affinity for their substrates. While ECF transporters are known to allow bacteria acquire essential trace nutrients, such as vitamins, this work is the first to identify a hemespecific ECF transporter. In the first manuscript published as part of this project, we identify the ECF transporter LhaSTA to facilitate heme acquisition. We found that S. lugdunensis produces LhaSTA strongly under iron-limited conditions, which mimic those encountered during infection. LhaSTA enables S. lugdunensis to grow using human heme and hemoglobin as a sole iron sources, resulting in cytoplasmic accumulation of the essential metal. We also demonstrate that purified LhaS protein exhibits strong affinity for heme and can accept heme from various host hemoproteins, including hemoglobin and myoglobin. Altogether, our experiments identify LhaSTA as the first heme-specific ECF transporter and highlight its importance for iron acquisition. In a further manuscript, we demonstrate that LhaSTA-mediated heme acquisition functions in conjunction with hemolytic toxins. S. lugdunensis secretes small peptides that damage host erythrocytes, releasing hemoglobin, which then serves as a source of nutritional iron for the pathogen. This study shows how hemolytic toxins and heme acquisition systems work in concert to help the pathogen overcome iron limitation during infection. Additionally, research funded by this project contributed to an international study showing that iron acquisition systems are critical virulence factors required by S. lugdunensis to cause infection in experimental animals. Finally, the scientists involved in this project also published review articles summarizing the virulence potential of S. lugdunensis.

Publications

• An ECF-type transporter scavenges heme to overcome iron-limitation in Staphylococcus lugdunensis. eLife, 9.
  Jochim, Angelika; Adolf, Lea; Belikova, Darya; Schilling, Nadine Anna; Setyawati, Inda; Chin, Denny; Meyers, Severien; Verhamme, Peter; Heinrichs, David E.; Slotboom, Dirk J. & Heilbronner, Simon
  
• Staphylococcus lugdunensis. Trends in Microbiology, 29(12), 1143-1145.
  Heilbronner, S.
  
• Staphylococcus lugdunensis: a Skin Commensal with Invasive Pathogenic Potential. Clinical Microbiology Reviews, 34(2).
  Heilbronner, Simon & Foster, Timothy J.
  
• In vivo growth of Staphylococcus lugdunensis is facilitated by the concerted function of heme and non-heme iron acquisition mechanisms. Journal of Biological Chemistry, 298(5), 101823.
  Flannagan, Ronald S.; Brozyna, Jeremy R.; Kumar, Brijesh; Adolf, Lea A.; Power, Jeffrey John; Heilbronner, Simon & Heinrichs, David E.
  
• SLUSH peptides of the PSMβ family enable Staphylococcus lugdunensis to use erythrocytes as a sole source of nutrient iron. The FASEB Journal, 38(16).
  Sekar, Sharmila; Schwarzbach, Selina; Nega, Mulugeta; Bloes, Dominik Alexander; Smeds, Emanuel; Kretschmer, Dorothee; Foster, Timothy J. & Heilbronner, Simon