Characterization of the orf1glnKamtB operon of Herbaspirillum seropedicae

Abstract

Herbaspirillum seropedicae is an endophytic nitrogen-fixing bacterium that colonizes economically important grasses. In this organism, the amtB gene is co-transcribed with two other genes: glnK that codes for a PII-like protein and orf1 that codes for a probable periplasmatic protein of unknown function. The expression of the orf1glnKamtB operon is increased under nitrogen-limiting conditions and is dependent on NtrC. An amtB mutant failed to transport methylammonium. Post-translational control of nitrogenase was also partially impaired in this mutant, since a complete switch-off of nitrogenase after ammonium addition was not observed. This result suggests that the AmtB protein is involved in the signaling pathway for the reversible inactivation of nitrogenase in H. seropedicae.

The involvement of the nif-associated ferredoxin-like genes fdxA and fdxN of Herbaspirillum seropedicae in nitrogen fixation

“…and H. seropedicae is that in the former the nitrogenase switch-off involves reversible ADP-ribosylation by the DraT and DraG enzymes (Martin and Reinhold-Hurek, 2002). In H. seropedicae the nitrogenase switch off/on occurs through an as yet unknown mechanism of post-translational regulation which involves the ammonia channel AmtB (Noindorf et al, 2006). The wild type switch-off phenotype of the fdxA mutant of H. seropedicae may be explained by the distinct mechanisms for nitrogenase post-translational control.…”

Uridylylation of Herbaspirillum seropedicae GlnB and GlnK proteins is differentially affected by ATP, ADP and 2-oxoglutarate in vitro

“…In this organism, all genes coding proteins involved in nitrogen metabolism were identified, including glnB, glnK, glnD, ntrB, ntrC and nifA (Souza et al 1991;Benelli et al 1997;Pedrosa et al 2001Pedrosa et al , 2011Noindorf et al 2006). Previous work showed that the H. seropedicae PII proteins GlnB and GlnK are uridylylated in vitro by GlnD.…”

Role of PII proteins in nitrogen fixation control of Herbaspirillum seropedicae strain SmR1

“…In this organism two PII-like coding genes were identified, glnB and glnK [14,15]. The glnB gene is monocistronic and its expression is constitutive [14], whereas glnK is apparently co-transcribed with amtB and orf1 , which encode for an ammonium transporter and a membrane associated protein of unknown function, respectively [15]. Recently orf1 was named nlmA ( n itrogen l imitation m embrane protein A) since its product was detected in membrane extracts of H. seropedicae grown under nitrogen-limitation conditions [16].…”

“…Recently orf1 was named nlmA ( n itrogen l imitation m embrane protein A) since its product was detected in membrane extracts of H. seropedicae grown under nitrogen-limitation conditions [16]. The expression of the nlmAglnKamtB operon is dramatically increased under nitrogen-limiting conditions and is dependent on NtrC [15]. As in other Proteobacteria , both PII proteins from H. seropedicae are targets of covalent modification by GlnD (uridylyl-transferase/uridylyl removing enzyme) in response to the levels of ammonium ions [17].…”