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Sinorhizobium meliloti chemotaxis to quaternary ammonium compounds is mediated by the chemoreceptor McpX
Author(s) -
Webb Benjamin A.,
Karl Compton K.,
Castañeda Saldaña Rafael,
Arapov Timofey D.,
Keith Ray W.,
Helm Richard F.,
Scharf Birgit E.
Publication year - 2017
Publication title -
molecular microbiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.857
H-Index - 247
eISSN - 1365-2958
pISSN - 0950-382X
DOI - 10.1111/mmi.13561
Subject(s) - sinorhizobium meliloti , biology , betaine , biochemistry , chemotaxis , enterococcus faecalis , ammonium , rhizobiaceae , microbiology and biotechnology , bacteria , mutant , escherichia coli , chemistry , symbiosis , genetics , receptor , organic chemistry , gene
Summary The bacterium Sinorhizobium meliloti is attracted to seed exudates of its host plant alfalfa ( Medicago sativa ). Since quaternary ammonium compounds (QACs) are exuded by germinating seeds, we assayed chemotaxis of S. meliloti towards betonicine, choline, glycine betaine, stachydrine and trigonelline. The wild type displayed a positive response to all QACs. Using LC–MS, we determined that each germinating alfalfa seed exuded QACs in the nanogram range. Compared to the closely related nonhost species, spotted medic ( Medicago arabica ), unique profiles were released. Further assessments of single chemoreceptor deletion strains revealed that an mcpX deletion strain displayed little to no response to these compounds. Differential scanning fluorimetry showed interaction of the isolated periplasmic region of McpX (McpX PR and McpX 34‐306 ) with QACs. Isothermal titration calorimetry experiments revealed tight binding to McpX PR with dissociation constants ( K d ) in the nanomolar range for choline and glycine betaine, micromolar K d for stachydrine and trigonelline and a K d in the millimolar range for betonicine. Our discovery of S. meliloti chemotaxis to plant‐derived QACs adds another role to this group of compounds, which are known to serve as nutrient sources, osmoprotectants and cell‐to‐cell signalling molecules. This is the first report of a chemoreceptor that mediates QACs taxis through direct binding.