INSTITUTO DE BIOTECNOLOGIA Y BIOLOGIA MOLECULAR
Unidad Ejecutora - UE
congresos y reuniones científicas
ROLE OF PII PROTEINS IN THE NITROGEN STRESS RESPONSE IN Bradyrhizobium diazoefficiens USDA 110
LAMELZA, F.; LÓPEZ GARCÍA, S.L.; HEGEL, V.
Congreso; LIII Reunión de La Sociedad Argentina de Investigación Bioquímica y Biología Molecular (SAIB 2017).; 2017
The NitrogenStress Response (NSR) is a specific mechanism that bacteria have developed toacquire and metabolize nitrogen (N) in an efficient way. The core elements ofNSR include an uridylyltransferase/uridylyl-cleavage enzyme, GlnD, and two PIIproteins: GlnB and GlnK. In N-starved cells, GlnD uridylylates PII proteinswhich, in turn, activates the bacterial NSR leading to more efficient ammoniumassimilation by increasing glutamine synthetase (GS) activity.The genomeof Bradyrhizobium diazoefficiensUSDA110, the N2-fixing symbiont of soybean plants, encodes one copyof glnB and two copies of glnK (called glnK1 and glnK2). Generally,rhizobia have only one copy of glnK,so we decided to investigate whether both copies are functional as well as understandthe role of the three PII proteins in the N metabolism.To achieveour objective we obtained mutants strains lacking glnK1 (ΔglnK1), glnK2 (ΔglnK2) or glnB (ΔglnB). The phenotype of the strains wasevaluated by monitoring growth kinetics in minimal medium containing 20mM of NH4Clas N source. Only ΔglnBmutant showed a significant delay in growth rate compared with WT strain. However,when we measured GS activity by ϒ-glutamiltransferaseassay, ΔglnK1 and ΔglnK2 showedhigher activity than WT meanwhile activity values of ΔglnB were lower.In view of theseresults and taking into account that in other bacteria GlnK could interact withAmtB (ammonium transporter) to regulate the NH4+ entranceto the bacteria, we decided to evaluate whether the lack of any PII affects theNH4+ uptake. Neither ΔglnK1nor ΔglnK2 showed significantdifference compared to the WT. Surprisingly, ΔglnB resulted strongly affected showing a pronounce decrease inthe amount of NH4+ able to get in the bacteria. The results suggestedthat both GlnK are functional in B.diazoefficiens and they are involved in GS activation. Moreover, the dataobtained showed that GlnB is crucial to sense N status and activate NSR infree-living bacteria.