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Appl. Environ. Microbiol. doi:10.1128/AEM.02702-07
Copyright (c) 2008, American Society for Microbiology and/or the Listed Authors/Institutions. All Rights Reserved.

Metabolic adaptation in Pseudomonas fluorescens evoked by aluminum and gallium toxicity: Involvement of fumarase C and NADH oxidase

Department of Chemistry and Biochemistry, Laurentian University, Sudbury, Ontario, Canada, P3E 2C6; International Center for Environmental Research, 47 Kostaya Str, 380079, Tbilisi, Georgia

^* To whom correspondence should be addressed. Email: vappanna{at}laurentian.ca.

	Abstract

Iron (Fe) is a critical element in all aerobic organisms as it participates in a variety of metabolic networks. In this study, aluminum (Al) and gallium (Ga), two Fe-mimetics, severely impeded the ability of the soil microbe, Pseudomonas fluorescens, to perform oxidative phosphorylation. This was achieved by disrupting the activity and expression of complexes I, II, and IV. These toxic metals also inactivated aconitase (ACN) and fumarase A (FUM A), two tricarboxylic acid (TCA) cycle enzymes dependent on Fe for their catalytic activity while fumarase C (FUM C), a Fe-independent enzyme, displayed an increase in activity and expression under these stressed situations. Furthermore, in the Al and Ga-exposed cells, the activity and expression of a H₂O-forming NADH oxidase (NOX), was markedly increased. The incubation of the Al and Ga-challenged cells in an Fe-containing medium led to the recovery of the affected enzymatic activities. Taken together, these data provide novel insights into how environmental pollutants such as Al and Ga interfere with cellular Fe metabolism and also illustrate the ability of Pseudomonas fluorescens to modulate metabolic networks to combat this situation.