Nickel uptake by Pseudomonas aeruginosa: role of modifying factors.
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 Km (6.15 mM) and increased Ni2+ uptake (950 nmol mg-1 protein, 1h) over cells pre-sown in minimal medium (Km, 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 microM 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.
Algal Research Laboratory, Centre of Advanced Study in Botany, Banaras Hindu University, Varanasi 221005, India.
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Sar
S K
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Kazy
R K
RK
Asthana
S P
SP
Singh
D002413:Cations, Divalent / Q000494:pharmacology; D003470:Culture Media; D004024:Dicyclohexylcarbodiimide / Q000494:pharmacology; D005947:Glucose / Q000494:pharmacology; D006863:Hydrogen-Ion Concentration; D017136:Ion Transport / Q000187:drug effects; D007700:Kinetics; D009532:Nickel / Q000378:metabolism*; D011550:Pseudomonas aeruginosa / Q000254:growth & development / Q000378:metabolism*; D012988:Soil Microbiology
D002413:Cations, Divalent; D003470:Culture Media; D004024:Dicyclohexylcarbodiimide; D009532:Nickel; D005947:Glucose