ExoS/ChvI Two-Component Signal-Transduction System Activated in the Absence of Bacterial Phosphatidylcholine

Abstract

Sinorhizobium meliloti contains the negatively charged phosphatidylglycerol and cardiolipin as well as the zwitterionic phosphatidylethanolamine (PE) and phosphatidylcholine (PC) as major membrane phospholipids. In previous studies we had isolated S. meliloti mutants that lack PE or PC. Although mutants deficient in PE are able to form nitrogen-fixing nodules on alfalfa host plants, mutants lacking PC cannot sustain development of any nodules on host roots. Transcript profiles of mutants unable to form PE or PC are distinct; they differ from each other and they are different from the wild type profile. For example, a PC-deficient mutant of S. meliloti shows an increase of transcripts that encode enzymes required for succinoglycan biosynthesis and a decrease of transcripts required for flagellum formation. Indeed, a PC-deficient mutant is unable to swim and overproduces succinoglycan. Some suppressor mutants, that regain swimming and form normal levels of succinoglycan, are altered in the ExoS sensor. Our findings suggest that the lack of PC in the sinorhizobial membrane activates the ExoS/ChvI two-component regulatory system. ExoS/ChvI constitute a molecular switch in S. meliloti for changing from a free-living to a symbiotic life style. The periplasmic repressor protein ExoR controls ExoS/ChvI function and it is thought that proteolytic ExoR degradation would relieve repression of ExoS/ChvI thereby switching on this system. However, as ExoR levels are similar in wild type, PC-deficient mutant and suppressor mutants, we propose that lack of PC in the bacterial membrane provokes directly a conformational change of the ExoS sensor and thereby activation of the ExoS/ChvI two-component system.

Membrane Homeoviscous Adaptation in Sinorhizobium Submitted to a Stressful Thermal Cycle Contributes to the Maintenance of the Symbiotic Plant–Bacteria Interaction

“…Underlying the process of homeoviscous adaptation is the stress-triggered catalytic activity of membrane bound enzymes (Solís-Oviedo et al, 2012) and/or membrane sensors related to signal transduction mechanisms (Geiger et al, 2021). Thus, the membrane remodeling in composition and organization may operate as an on/off switch on the controlling mechanisms.…”

“…Interestingly, the transition to 40 • C, although it did not affect the U/S OM , a decrease in the mean length of the acyl chains of saturated FA was observed, by increasing 16:0 and decreasing. Underlying the process of homeoviscous adaptation is the stress-triggered catalytic activity of membrane-bound enzymes (Solís-Oviedo et al, 2012) and/or membrane sensors related to signal transduction mechanisms (Geiger et al, 2021). Thus, the membrane remodeling in composition and organization may operate as an on/off switch on the controlling mechanisms 18:0.…”

Formation of sulfoquinovosyl diacylglycerol by acylation of sulfoquinovosyl glycerol

“…In some cases, as in ( B ), CL and MMPE were not completely separated and were quantified together. In the examples shown here, the complex medium used was LB/MC containing 10 mM CaCl 2 that confers similar growth rate to strains 1021, CS111 and OG10017 (Geiger et al ., 2021).…”

The <em>Sinorhizobium Meliloti</em> Nsps-Mbaa System affects Biofilm Formation, Exopolysaccharide Production and Motility in Response to Specific Polyamines

“…The ExpR/SinI QS system controls EPS II and ß-glucan biosynthesis and affects biofilm formation. EPS I production, biofilm formation and motility are also controlled by the ExoR-ExoS/ChvI signalling pathway.Although the transcriptional regulator MucR also affects EPS I and EPS II synthesis it does not greatly alter biofilm formation nor does mucR transcription respond to environmental cues [5,12,17,18].…”