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We identified the extremely nitrite-tolerant bacterium Achromobacter denitrificans YD35 that can grow in complex medium containing 100 mM nitrite (NO2－) under aerobic conditions. Nitrite induced global proteomic changes and upregulated tricarboxylate (TCA) cycle enzymes as well as antioxidant proteins in YD35. Transposon mutagenesis generated NO2－-hypersensitive mutants of YD35 that had mutations at genes for aconitate hydratase and α-ketoglutarate dehydrogenase in the TCA cycle and a pyruvate dehydrogenase (Pdh) E1 component, indicating the importance of TCA cycle metabolism to NO2－ tolerance. A mutant in which the pdh gene cluster was disrupted (Δpdh mutant) could not grow in the presence of 100 mM NO2－. Nitrite decreased the cellular NADH/NAD+ ratio and the cellular ATP level. These defects were more severe in the Δpdh mutant, indicating that Pdh contributes to upregulating cellular NADH and ATP and NO2－-tolerant growth. Exogenous acetate, which generates acetyl coenzyme A and then is metabolized by the TCA cycle, compensated for these defects caused by disruption of the pdh gene cluster and those caused by NO2－. These findings demonstrate a link between NO2－ tolerance and pyruvate/acetate metabolism through the TCA cycle. The TCA cycle mechanism in YD35 enhances NADH production, and we consider that this contributes to a novel NO2－-tolerating mechanism in this strain.
Achromobacter denitrificans Strain YD35 Pyruvate Dehydrogenase Controls NADH Production To Allow Tolerance to Extremely High Nitrite Levels
Research papers (academic journals)
