Table 1.
Quorum-sensing systems in symbiotic rhizobia.
| Rhizobial Strain | QS Signal | Genes | Phenotypes Regulated | References |
|---|---|---|---|---|
|
Bradyrhizobium japonicum
(B. diazoefficiens) |
||||
| USDA110 | Bradyoxetin | Unknown | nod gene regulation | [20,64] |
| Isovaleryl-HL | bjaI/bjaR1 | Unknown. | [21] | |
| USDA290 and other strains | Non-characterized AHL | Unknown | Unknown | [65] |
| Bradyrhizobium spp. | ||||
| ORS278 | Cinnamoyl-HL | braI/braR | Unknown | [22] |
| Peanut-nodulating strains | C6-HL, 3-oxo-C10-HL, 3-oxo-C12-HL, 3-oxo-C14-HL | Unknown | Motility, biofilm formation, cell aggregation a | [66] |
| SR-6 | C6-HL, 3-OH-C6-HL, C8-HL, C10-HL, 3-oxo-C10-HL, 3-oxo-C12-HL, 3-OH-C12-HL | Unknown | Nodulation b | [67] |
| Mesorhizobium loti | ||||
| NZP2213 | 3-oxo-C6-HL, C8-HL, C10-HL | mrlI2 | Unknown | [68] |
| C12-HL | mrlI1 | Nodulation | ||
| R7A | 3-oxo-C6-HL | traI1/traR | Symbiosis island transfer | [69] |
| C4-HL, 3-oxo-C12-HL | Unknown | Unknown | ||
| Mesorhizobium tianshanense | ||||
| CCBAU3306 | 3-oxo-C6-HL c, 3-oxo-C8-HL c | mrtI/mrtR | Nodulation (Nod-) | [70] |
| CCBAU060A | 3-oxo-C6-HL c, 3-oxo-C8-HL c, 3-oxo-C12-HL c | mtqI/mtqR/ mtqS | Growth rate, nodulation | [71] |
| Mesorhizobium huakuii | ||||
| CCBAU21173 | Peptide-related signal | Putative peptidase | Growth rate, biofilm formation, nodulation (Nod-) | [72] |
| Rhizobium etli | ||||
| CNPAF512 | 3-OH-(slc)-HL d | cinI/cinR | Nitrogen fixation, symbiosome development, growth rate, swarming | [73,74] |
| Short-chain AHLs c | raiI/raiR | Nodulation | [75] | |
| CFN42 | C8-HL c, 3-oxo-C6-HL c, 3-oxo-C8-HL c |
cinI/cinR
raiI/raiR |
Nodulation, nitrogen fixation | [17,76] |
| 3-oxo-C8-HL, 3-OH-C8-HL c | traI/traR1/traR2 | Plasmid transfer, nitrogen fixation, | [17,76,77] | |
| RT1 | 3-oxo-C8-HL, 3-OH-C14-HL | Unknown | Swarming, biofilm formation a | [78] |
| Rhizobium leguminosarum | ||||
| bv. viciae | 3-OH-C14:1-HL | cinI/cinR/cinS | Growth inhibition, regulation of EPS cleavage, biofilm formation | [79,80,81] |
| C6-HL, C7-HL, C8-HL | rhiI/rhiR | Nodulation e | [4,82] | |
| 3-oxo-C8-HL, C8-HL | trai/traR, bisR | Plasmid transfer | [4,83] | |
| C6-HL, C7-HL, C8-HL, 3-OH-C8-HL | raiI/raiR | Unknown | [84] | |
| Unknown effector | expR | Regulation of EPS cleavage, biofilm formation |
[80,81] | |
| Sinorhizobium fredii | ||||
| SMH12 | C8-HL, C14-HL 3-oxo-C8-HL |
Unknown traI/traR |
Biofilm formation Plasmid transfer |
[85,86] |
| NGR234 | 3-oxo-C8-HL | traI/traR | Plasmid transfer, growth rate, sedimentation, motility, biofilm formation, regulation of EPS genes, regulation of the copy number of the symbiotic plasmid | [87,88,89] |
| Non-characterized AHL c | ngrI/ngrR | |||
|
Sinorhizobium meliloti
(Ensifer meliloti) |
||||
| Rm1021 | C12-HL, C14-HL, 3-oxo-C14-HL, C16-HL, 3-oxo-C16-HL, C16:1-HL, 3-oxo-C16:1-HL, C18-HL | sinI/sinR, expR | EPS production, surface translocation, regulation of motility genes, growth rate, nodulation | [16,24,25,26,28,34,36,37,38,39,40,43,90,91] |
| Rm41 f | 3-oxo-C8-HL | traI/traR | Plasmid transfer | [27] |
a Effects observed by adding synthetic AHLs. b Effects observed by adding purified extracts of AHLs. c Detected by using biosensors but not characterized by mass spectrometry analysis. d Saturated long chain 3-hydroxy-acyl-HL. e Only in a mutant strain already compromised for nodulation. f Rm41 also harbors the ExpR/Sin system of Rm1021