Methylammonium uptake by Rhodobacter capsulatus

AmtB Is Necessary for NH 4 + -Induced Nitrogenase Switch-Off and ADP-Ribosylation in Rhodobacter capsulatus

“…Previously it has been shown that R. capsulatus appears to possess two ammonium uptake systems; one that is constitutively synthesized and a second system, capable of transporting methylammonium, that seems to be under global nitrogen control (34). Since the presence of nitrogenase switch-off in R. capsulatus is correlated with an increased activity of the second NH 4 ϩ uptake system (50), we suggested that the nitrogenase switch-off system responds to a signal generated by this NH 4 ϩ transport system.…”

Ammonia-dependent growth (Adg-) mutants of Rhodobacter capsulatus and Rhodobacter sphaeroides: comparison of mutant phenotypes and cloning of the wild-type (adg A) genes

“…In R . capsulatus, it has been shown that methylammonium uptake is tightly coupled to its metabolism via GS (Rapp et al, 1986), so the loss of uptake activity in the Adg-mutants might have been due to an inability to metabolize methylamine. The biosynthetic activity of GS has been measured in Adgmutants of R. sphaeroides grown on glutamine, and was found to be 25-40% of the wild-type activity (Shestakov et al, 1988).…”

“…Methylammonium uptake was assayed essentially as described by Rapp et al (1986). Cells grown for transport studies (4 ml of a culture grown to mid-exponential phase in Ormerod medium) were harvested by centrifugation.…”

“…capsulatus and R . sphaeroides both conta n a methylammonium transport system, which is present in glutamate-grown or N,-grown cells, but lot in cells grown on NH,+ (Alef & Kleiner, 1982;Rapp et al, 1986;Cordts & Gibson, 1987). Methylammonium uptake is inhibited by low concentrations of NH,+ ions, implying that uptake of methylammonium is due to an NH,+ transport system.…”

“…In contrast, disruption of the nifR1, nifR2 or nzfR4 genes in R. capsulatus results in a Nif-phenotype, but not in an Ntr-phenotype, suggesting that the genes involved are specifically involved in controlling nitrogen fixation. However, a nifRl mutant, 561, in addition to being unable to synthesize nitrogenase, is also unable to synthesize an inducible methylammonium (ammonium) uptake system (Haselkorn, 1986;Rapp et al, 1986).…”