2-Oxoglutarate transport system in Staphylococcus aureus

Abstract.

2-[¹⁴C]oxoglutarate uptake in resting cells of Staphylococcus aureus 17810S occurs via two kinetically different systems: (1) a secondary, electrogenic 2-oxoglutarate:H⁺ symporter (K _m=0.105 mM), energized by an electrochemical proton potential (Δµ_H+) that is generated by the oxidation of endogenous amino acids and sensitive to ionophores, and (2) a Δµ_H+-independent facilitated diffusion system (K _m=1.31 mM). The 2-oxoglutarate transport system of S. aureus 17810S can be classified as a new member of the MHS (metabolite:H⁺ symporter) family. This transporter takes up various dicarboxylic acids in the order of affinity: succinate = malate > fumarate > 2-oxoglutarate > glutamate. Energy conservation with 2-oxoglutarate was studied in starved cells of strain 17810S. Initial transport of 2-oxoglutarate in these cells is energized by Δµ_H+ generated via hydrolysis of residual ATP. Subsequent oxidation of the accumulated 2-oxoglutarate generates Δµ_H+ for further, autoenergized transport of this 2-oxoacid and also for Δµ_H+-linked resynthesis of ATP. In the cadmium-sensitive S. aureus 17810S, Cd²⁺ accumulation strongly inhibits energy conservation with 2-oxoglutarate at the level of Δµ_H+ generation, without direct blocking of the 2-oxoglutarate transport system or ATP synthase complex. In the cadmium-resistant S. aureus 17810R, Cd²⁺ does not affect energy conservation due to its extrusion by the Cd²⁺ efflux system (Cd²⁺-ATPase of P-type), which prevents Cd²⁺ accumulation.