Download MendeleySinorhizobium meliloti, a bacterium lacking the autoinducer-2 (AI-2) synthase, responds to AI-2 supplied by other bacteria.
Pereira, C.S., McAuley, J.R., Taga, M.E., Xavier, K.B., Miller, S.T.(2008) Mol Microbiol 70: 1223-1235
- PubMed: 18990189
- DOI: https://doi.org/10.1111/j.1365-2958.2008.06477.x
- Primary Citation of Related Structures:
3EJW - PubMed Abstract:
Many bacterial species respond to the quorum-sensing signal autoinducer-2 (AI-2) by regulating different niche-specific genes. Here, we show that Sinorhizobium meliloti, a plant symbiont lacking the gene for the AI-2 synthase, while not capable of producing AI-2 can nonetheless respond to AI-2 produced by other species. We demonstrate that S. meliloti has a periplasmic binding protein that binds AI-2. The crystal structure of this protein (here named SmlsrB) with its ligand reveals that it binds (2R,4S)-2-methyl-2,3,3,4-tetrahydroxytetrahydrofuran (R-THMF), the identical AI-2 isomer recognized by LsrB of Salmonella typhimurium. The gene encoding SmlsrB is in an operon with orthologues of the lsr genes required for AI-2 internalization in enteric bacteria. Accordingly, S. meliloti internalizes exogenous AI-2, and mutants in this operon are defective in AI-2 internalization. S. meliloti does not gain a metabolic benefit from internalizing AI-2, suggesting that AI-2 functions as a signal in S. meliloti. Furthermore, S. meliloti can completely eliminate the AI-2 secreted by Erwinia carotovora, a plant pathogen shown to use AI-2 to regulate virulence. Our findings suggest that S. meliloti is capable of 'eavesdropping' on the AI-2 signalling of other species and interfering with AI-2-regulated behaviours such as virulence.
Organizational Affiliation:
Bacterial Signaling Laboratory, Instituto Gulbenkian de Ciência, Oeiras, Portugal.
