Inhibitor effects on the accumulation and efflux of nickel ions in plasmid pMOL28-harboring strains of Alcaligenes eutrophus

Abstract

The accumulation and efflux of 63Ni2+ ions were studied using two strains of the strictly respiratory bacterium Alcaligenes eutrophus, the wild type strain N9A and its transconjugant N9A-M243 which harbors plasmid pMOL28.1 encoding constitutive resistance to nickel. When 1 μM 63Ni2+ is added to respiring cells, strain N9A accumulates high, but M243 only negligibly small amounts of nickel. When the cells were preincubated for about 20 h under anoxic conditions and were then exposed to 1 μM 63Ni2+ anaerobically, both strains accumulated approximately the same amounts of nickel. Aeration of these preloaded cells resulted in rapid efflux by strain M243 but renewed uptake of nickel by N9A. 63Ni2+ uptake and efflux are highly sensitive to protonophores such as CCCP, FCCP and TCS but insensitive to DCCD (each at 20 μM concentrations). Measurements on the effects of the inhibitors on biosynthetic processes requiring ATP either from substrate phosphorylation or from electron transport phosphorylation made sure that at the concentrations used the inhibitor effects were specific. Thus the results suggest that in the nickelresistant strain M243 under normal aerobic conditions two constitutive energy-dependent nickel transport systems can function concomitantly, a chromosomally-determined specific uptake system and a plasmid-mediated specific nickel efflux system.