Involvement of Fumarase C and NADH Oxidase in Metabolic Adaptation ofPseudomonas fluorescensCells Evoked by Aluminum and Gallium Toxicity

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 cycle enzymes dependent on Fe for their catalytic activity, while FUM C, an 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 an H 2 O-forming NADH oxidase were 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.

The role of formate in combatting oxidative stress

“…This metabolite aided by the enzymes ME and ICDH-NADP, may allow P. fluorescens to battle the oxidative challenge posed by H2O2. Indeed, various organisms are shown to evoke intricate NADPH-generating pathways to modulate their NADPH budget to combat oxidative stress Chenier et al, 2008;Drummond et al, 2011;Spanier et al, 2009). …”

“…Additionally, oxidative phosphorylation is downregulated as revealed by the diminished activity of Complex I, a situation that may impede the generation of 28 NAD. To rectify such an occurrence, the microbe invokes the participation of NADH oxidase, an enzyme whose activity is known to be increased during environmental stress (Chenier et al, 2008).…”

The Antibacterial Activity of Ga3+Is Influenced by Ligand Complexation as Well as the Bacterial Carbon Source

“…Chenier et al found that as a consequence of the pronounced stress in the presence of Ga or Al, P. fluorescens responds with active reorganization of its metabolic pathways to use the tricarboxylic acid (TCA) cycle (12,32). At present, it is not known whether pathogenic bacteria possess similar mechanisms and how the presence or absence of such mechanisms can affect their virulence.…”

“…It has been shown that Ga and another Fe mimetic, Al, have severe toxicity for Pseudomonas fluorescens, impeding the functionality of the electron transport chain and enzymes containing Fe-S clusters (12). Chenier et al found that as a consequence of the pronounced stress in the presence of Ga or Al, P. fluorescens responds with active reorganization of its metabolic pathways to use the tricarboxylic acid (TCA) cycle (12,32).…”

“…The antibacterial properties of Ga are generally attributed to its ability to substitute for Fe 3ϩ in bacterial metabolism. Unlike Fe, Ga cannot redox cycle, and as a consequence, it blocks multiple processes in bacteria where the shift between reduced and oxidized iron (Fe 2ϩ and Fe 3ϩ ) is crucial (7,12). It was suggested that in P. aeruginosa, Ga decreases the uptake of Fe by disrupting Fe signaling through repression of pvdS, which encodes a sigma factor that enables transcription of the genes for pyoverdine synthesis.…”