An ATP and Oxalate Generating Variant Tricarboxylic Acid Cycle Counters Aluminum Toxicity in Pseudomonas fluorescens

Abstract

Although the tricarboxylic acid (TCA) cycle is essential in almost all aerobic organisms, its precise modulation and integration in global cellular metabolism is not fully understood. Here, we report on an alternative TCA cycle uniquely aimed at generating ATP and oxalate, two metabolites critical for the survival of Pseudomonas fluorescens. The upregulation of isocitrate lyase (ICL) and acylating glyoxylate dehydrogenase (AGODH) led to the enhanced synthesis of oxalate, a dicarboxylic acid involved in the immobilization of aluminum (Al). The increased activity of succinyl-CoA synthetase (SCS) and oxalate CoA-transferase (OCT) in the Al-stressed cells afforded an effective route to ATP synthesis from oxalyl-CoA via substrate level phosphorylation. This modified TCA cycle with diminished efficacy in NADH production and decreased CO2-evolving capacity, orchestrates the synthesis of oxalate, NADPH, and ATP, ingredients pivotal to the survival of P. fluorescens in an Al environment. The channeling of succinyl-CoA towards ATP formation may be an important function of the TCA cycle during anaerobiosis, Fe starvation and O2-limited conditions.

Bacterial quorum sensing, cooperativity, and anticipation of stationary-phase stress

“…In bacteria, oxalate synthesis more commonly occurs through a separate pathway involving glyoxylate as an intermediate (36,37); however, we found no evidence of this pathway in any of the three Burkholderia species that we studied. We show that Obc1 is responsible for oxalate synthesis in B. thailandensis.…”

Glyoxylate Metabolism Is a Key Feature of the Metabolic Degradation of 1,4-Dioxane by Pseudonocardia dioxanivorans Strain CB1190

“…While the transformation of glyoxylate to oxalate has been reported in Pseudomonas fluorescens (40), the gene sequence for the enzyme catalyzing this reaction has not yet been determined in bacteria. Finally, aerobic bacterial growth on oxalate was shown to be dependent on the oxalate decarboxylase OxdC, which converts oxalate to formate (45).…”

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

“…Additionally, Fur regulates expression of small RNAs, RyhB in E. coli and V. cholerae and PrrF1 and PrrF2 in P. aeruginosa (38,51), responsible for translational inhibition of the synthesis of nonessential Fe proteins as a part of an iron-saving strategy when Fe is limited. Electron transport chain proteins involved in oxidative phosphorylation often depend on heme, and it is thought that when Fe is limited, heme biosynthesis becomes ineffective (38,47). The presence of Al, which like Ga disturbs Fe metabolism, drives P. fluorescens to produce ATP through a modified TCA cycle instead of oxidative phosphorylation (47).…”

“…Electron transport chain proteins involved in oxidative phosphorylation often depend on heme, and it is thought that when Fe is limited, heme biosynthesis becomes ineffective (38,47). The presence of Al, which like Ga disturbs Fe metabolism, drives P. fluorescens to produce ATP through a modified TCA cycle instead of oxidative phosphorylation (47). This type of compensatory mechanism involving the TCA cycle has also been shown to appear in S. aureus during Fe starvation (20).…”