Rhizobium leguminosarum bv. trifolii rosR is required for interaction with clover, biofilm formation and adaptation to the environment

Abstract

BackgroundRhizobium leguminosarum bv. trifolii is a symbiotic nitrogen-fixing bacterium that elicits nodules on roots of host plants Trifolium spp. Bacterial surface polysaccharides are crucial for establishment of a successful symbiosis with legumes that form indeterminate-type nodules, such as Trifolium, Pisum, Vicia, and Medicago spp. and aid the bacterium in withstanding osmotic and other environmental stresses. Recently, the R. leguminosarum bv. trifolii RosR regulatory protein which controls exopolysaccharide production has been identified and characterized.ResultsIn this work, we extend our earlier studies to the characterization of rosR mutants which exhibit pleiotropic phenotypes. The mutants produce three times less exopolysaccharide than the wild type, and the low-molecular-weight fraction in that polymer is greatly reduced. Mutation in rosR also results in quantitative alterations in the polysaccharide constituent of lipopolysaccharide. The rosR mutants are more sensitive to surface-active detergents, antibiotics of the beta-lactam group and some osmolytes, indicating changes in the bacterial membranes. In addition, the rosR mutants exhibit significant decrease in motility and form a biofilm on plastic surfaces, which differs significantly in depth, architecture, and bacterial viability from that of the wild type. The most striking effect of rosR mutation is the considerably decreased attachment and colonization of root hairs, indicating that the mutation affects the first stage of the invasion process. Infection threads initiate at a drastically reduced rate and frequently abort before they reach the base of root hairs. Although these mutants form nodules on clover, they are unable to fix nitrogen and are outcompeted by the wild type in mixed inoculations, demonstrating that functional rosR is important for competitive nodulation.ConclusionsThis report demonstrates the significant role RosR regulatory protein plays in bacterial stress adaptation and in the symbiotic relationship between clover and R. leguminosarum bv. trifolii 24.2.

The response of the Rhizobium leguminosarum bv. trifolii wild-type and exopolysaccharide-deficient mutants to oxidative stress

“…Previously, it was observed that the pssA mutant totally defective in EPS synthesis induced almost empty nodules inefficient in nitrogen fixation. Additionally, the rosR mutant produced 3-fold less EPS and elicited significantly fewer nodules, which were occupied by ten times fewer bacteria than the wild-type strain (Janczarek et al 2009a(Janczarek et al , 2010. The part-after-part estimation of the several enzymatic as well as non-enzymatic biochemical and physiological features of the wild-type and the pssA and rosR mutants cultured under oxidative stress conditions confirmed the crucial role of these genes involved in EPS synthesis in oxidative stress defence mechanisms.…”

“…Our previous studies indicated that mutations in rosR and pssA genes resulted in several pleiotropic effects, among them disturbances in membrane integrity causing unspecific protein leakage (Janczarek et al 2009a(Janczarek et al , 2010. Therefore, the levels of both extracellular and intracellular SOD activity have been determined.…”

“…Moreover, the rosR mutant shows several other pleiotropic effects such as increased sensitivity to surface-active detergents and some osmolytes, changes in extracellular and membrane protein profiles, and decreased ability to infect roots of the host plant, indicating that the product of this gene is involved in the adaptation of R. leguminosarum bv. trifolii to stress conditions (Janczarek et al 2010). On the other hand, multiple copies of rosR and pssA genes significantly enhance EPS production and the number of nodules induced on clover roots (Janczarek et al 2009a).…”

Intruders below the Radar: Molecular Pathogenesis of Bartonella spp

“…Like the BatR/BatS system, other transcriptional regulators have been hit in the STM screens and may thus participate in coordinating the expression of the huge arsenal of Bartonella virulence factors. One of those, RosR (374), is well known to be essential for productive host interaction in other Rhizobiales such as Sinorhizobium (207).…”

Mutation of the Sensor Kinase chvG in Rhizobium leguminosarum Negatively Impacts Cellular Metabolism, Outer Membrane Stability, and Symbiosis

“…In R. leguminosarum bv. trifolii, the pssA gene is positively regulated by the transcriptional regulator RosR (15). Mutants of rosR have phenotypes similar to those described for chvG, including alterations in membrane stability, decreased levels of ropB expression, and symbiotic defects, suggesting that there may be overlap between the regulons of ChvG/ChvI and RosR (16).…”