| Many bacteria exchange N-acyl homoserine lactone (AHL) signal molecules to coordinate the behavior of individual cells. Such quorum sensing regulation controls many bacterial behaviors. The nitrogen-fixing symbiotic bacterium Sinorhizobium meliloti was found to produce AHLs with C14–C16 alkanoyl, alkenoyl and 3-oxo-alkenoyl side chains. In addition, some strains of S. meliloti also produced AHLs with C6–C10 alkanoyl and 3-oxo-alkanoyl side chains. Exposure of early log phase cells of wildtype S. meliloti 1021 to purified C14-HL and 3-oxo-C16:1-HL changed the accumulation of over a hundred polypeptides involved in stress responses, nitrogen and carbon cycling and utilization, nucleotide and secondary metabolite synthesis. These results provide the first global analysis of quorum sensing regulation in S. meliloti.; Seedlings of pea, Medicago truncatula, soybean, rice and tomato and cells of the unicellular alga Chlamydomonas reinhardtii were capable of producing substances that mimicked bacterial AHLs in well-characterized AHL reporter strains. This is the first demonstration of AHL signal-mimic compounds in eukaryotes after their discovery in a marine alga, and indicates that plants and algae may have a general ability to disrupt quorum sensing regulation in associated bacteria through secretion of quorum sensing signal mimics. Initial HPLC fractionation of AHL-mimics from plants separated about a half-dozen different activities, each affecting a different set of AHL receptors. AHL-mimics from plants may have important agricultural and industrial applications in controlling bacterial communities.; Exudates of pea seedlings were separated based on molecular weight. Low molecular weight components included the AHL-mimic compounds while the high molecular weight fraction contained root mucilage (complex polysaccharide-glycoprotein material). Rhizobium leguminosarum, a bacterial symbiont of pea, could use pea root mucilage and plant polysaccharides as sole carbon sources. Growth of R. leguminosarum on root mucilage, but not on the polysaccharides, was enhanced by the addition of micromolar concentrations of nod-gene inducing plant flavonoids. Several mutants of R. leguminosarum with altered glycosidase activity were isolated, none of which was affected in the ability to grow on root mucilage or other plant polysaccharides. |
