Member of the two-component regulatory system PhoP/PhoQ that plays a role in the regulation of resistance towards polymyxin B and cationic antimicrobial peptides in response to limiting concentrations of Mg(2+) (PubMed:10564474, PubMed:11021929, PubMed:16707691). May function as a membrane-associated protein kinase that phosphorylates PhoP in response to environmental signals leading to activation of specific gene promoters (Probable). ATP + protein L-histidine = ADP + protein N-phospho-L-histidine. Deletion mutant displays significantly lower virulence than the wild-type strain (PubMed:10564474). Also exhibits a constitutive polymyxin B resistance (PubMed:11021929).