Protection of Sinorhizobium against host cysteine-rich antimicrobial peptides is critical for symbiosis

Andreas F Haag, Mikhail Baloban, Monica Sani, Bernhard Kerscher, Olivier Pierre, Attila Farkas, Renato Longhi, Eric Boncompagni, Didier Hérouart, Sergio Dall'angelo, Eva Kondorosi, Matteo Zanda, Peter Mergaert, Gail P Ferguson

Research output: Contribution to journalArticlepeer-review


Sinorhizobium meliloti differentiates into persisting, nitrogen-fixing bacteroids within root nodules of the legume Medicago truncatula. Nodule-specific cysteine-rich antimicrobial peptides (NCR AMPs) and the bacterial BacA protein are essential for bacteroid development. However, the bacterial factors central to the NCR AMP response and the in planta role of BacA are unknown. We investigated the hypothesis that BacA is critical for the bacterial response towards NCR AMPs. We found that BacA was not essential for NCR AMPs to induce features of S. meliloti bacteroids in vitro. Instead, BacA was critical to reduce the amount of NCR AMP-induced membrane permeabilization and bacterial killing in vitro. Within M. truncatula, both wild-type and BacA-deficient mutant bacteria were challenged with NCR AMPs, but this resulted in persistence of the wild-type bacteria and rapid cell death of the mutant bacteria. In contrast, BacA was dispensable for bacterial survival in an M. truncatula dnf1 mutant defective in NCR AMP transport to the bacterial compartment. Therefore, BacA is critical for the legume symbiosis by protecting S. meliloti against the bactericidal effects of NCR AMPs. Host AMPs are ubiquitous in nature and BacA proteins are essential for other chronic host infections by symbiotic and pathogenic bacteria. Hence, our findings suggest that BacA-mediated protection of bacteria against host AMPs is a critical stage in the establishment of different prolonged host infections.

Original languageEnglish
Pages (from-to)e1001169
JournalPLoS Biology
Issue number10
Publication statusPublished - 4 Oct 2011


  • Amino Acid Sequence
  • Antimicrobial Cationic Peptides/chemistry
  • Bacterial Proteins/metabolism
  • Cysteine/metabolism
  • Host-Pathogen Interactions/drug effects
  • Medicago truncatula/drug effects
  • Microbial Viability/drug effects
  • Molecular Sequence Data
  • Mutation/genetics
  • Protein Structure, Secondary
  • Sinorhizobium meliloti/cytology
  • Symbiosis/drug effects


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