A novel metabolic network leads to enhanced citrate biogenesis in Pseudomonas fluorescens exposed to aluminum toxicity.
Aluminum (Al), an environmental toxin, is known to have a negative impact on various biological systems. However, some microbes have devised intricate mechanisms to combat the toxic influence of this trivalent metal. In this study, Pseudomonas fluorescens grown in malate invoked a unique metabolic shift to promote the synthesis of citrate, a metabolite involved in the sequestration of Al. Electrophoretic and spectrophotometric assays revealed several malate-metabolizing enzymes including malate dehydrogenase (MDH) and malic enzyme (ME) displayed increases in activity and expression in the Al-treated cells. Whereas pyruvate dehydrogenase (PDH) also showed increased activity and expression in the Al-stressed cultures, phosphoenolpyruvate carboxykinase (PEPCK) displayed a marked diminution in the Al-treated cells. The upregulation of citrate synthase (CS) coupled with the diminished activities of aconitase (ACN) and NAD-isocitrate dehydrogenase (NAD-ICDH) appeared to be instrumental in the accumulation of citrate. HPLC experiments revealed high levels of citrate in the Al-stressed cultures. Thus, an Al-enriched environment provoked a metabolic shift in P. fluorescens dedicated to the conversion of malate to citrate.
Mailloux
Ryan J
RJ
Department of Chemistry and Biochemistry, Laurentian University, Sudbury, ON, Canada P3E 2C6.
Lemire
Joseph
J
Kalyuzhnyi
Sergey
S
Appanna
Vasu
V
D000154:Aconitate Hydratase / Q000378:metabolism; D000222:Adaptation, Physiological; D000077410:Aluminum Chloride; D017607:Aluminum Compounds / Q000633:toxicity*; D001426:Bacterial Proteins / Q000378:metabolism; D002712:Chlorides / Q000633:toxicity*; D002950:Citrate (si)-Synthase / Q000378:metabolism; D019343:Citric Acid / Q000378:metabolism*; D004734:Energy Metabolism / Q000187:drug effects*; D004785:Environmental Pollutants / Q000633:toxicity*; D007521:Isocitrate Dehydrogenase / Q000378:metabolism; D007658:Ketone Oxidoreductases / Q000378:metabolism; D008291:Malate Dehydrogenase / Q000378:metabolism; D008293:Malates / Q000378:metabolism; D010730:Phosphoenolpyruvate Carboxylase / Q000378:metabolism; D011551:Pseudomonas fluorescens / Q000187:drug effects* / Q000201:enzymology / Q000378:metabolism; D013997:Time Factors
D017607:Aluminum Compounds; D001426:Bacterial Proteins; D002712:Chlorides; D004785:Environmental Pollutants; D008293:Malates; D019343:Citric Acid; D000077410:Aluminum Chloride; C030298:malic acid; D008291:Malate Dehydrogenase; D007521:Isocitrate Dehydrogenase; D007658:Ketone Oxidoreductases; C053164:pyruvate dehydrogenase (NADP+); D002950:Citrate (si)-Synthase; D010730:Phosphoenolpyruvate Carboxylase; D000154:Aconitate Hydratase