Nickel Uptake by Pseudomonas aeruginosa: Role of Modifying Factors

Abstract.

Pseudomonas aeruginosa cells growing in minimal medium were 40-fold more sensitive to Ni²⁺ than cells growing in enriched medium, suggesting a possible protective role of medium ingredients. Likewise, cells pre-grown in enriched medium showed a high K _m (6.15 mM) and increased Ni²⁺ uptake (950 nmol mg⁻¹ protein, 1h) over cells pre-sown in minimal medium (K _m , 0.48 mM; 146 nmol mg⁻¹ protein, 1 h). The overall pattern indicates that cells pre-grown in enriched medium were characterized by having lowered affinity towards Ni²⁺ than those with minimal medium background. The enhanced Ni²⁺ uptake by enriched medium-grown cells can be correlated with the improved metabolic state of the cells. Ni²⁺ uptake was optimum at neutrality (pH 7.0). A major Ni²⁺ transport system was competitively inhibited by Mg²⁺, Zn²⁺, Cd²⁺, or Co²⁺ (400 μM each). Noticeably, a minor Ni²⁺ transport pathway was still operative even in the higher concentration range of Mg²⁺ (4 mM and 40 mM). The stimulation of Ni²⁺ uptake monitored in the presence of different carbon sources (0.5% wt/vol, each) showed the sequence: glucose (1.6-fold) > phenol = gallic acid (1.5-fold). Succinate, in comparison, reduced Ni²⁺ uptake (0.5-fold) possibly because of its acting as a metal chelator as well. Sensitivity of Ni²⁺ transport towards methyl viologen, azide, 2-4 DNP, and DCCD suggested that transport was energy-linked.