Novel function assignment to a member of the essential HP1043 response regulator family of epsilon-proteobacteria

HP1043 of Helicobacter pylori is an orphan response regulator (RR) with a highly degenerate receiver sequence incapable of phosphorylation, which is essential for cell viability. In contrast, the orthologous RR protein of Helicobacter pullorum, an enterohepatic Helicobacter species mainly isolated from poultry, harbours a consensus receiver sequence and is associated with a cognate histidine kinase (HK). Here, we show that this two-component system of H. pullorum, denoted HPMG439/HPMG440, is involved in the control of nitrogen metabolism by regulating the expression of glutamate dehydrogenase, an AmtB ammonium transporter and a PII protein. However, the role of the RR HPMG439 is not restricted to nitrogen regulation since, in contrast with the HK HPMG440, HPMG439 is essential for growth of H. pullorum under nutrient-rich conditions.