Extracellular Acidic pH Inhibits Acetate Consumption by Decreasing Gene Transcription of the Tricarboxylic Acid Cycle and the Glyoxylate Shunt

Many microorganisms produce fermentation products during aerobic growth on sugars. One of the best-known examples is the production of acetate byEscherichia coli during aerobic growth on sugars. InE. coli , acetate production is reversible: once the cells consume the available sugar, they can consume the acetate previously produced during aerobic fermentation. We found that pH affects the reversibility of acetate production. When the cells produce significant acetate during growth in acidic environments, they are unable to consume it. Unconsumed acetate may accumulate in the cell and inhibit the expression of pathways required for acetate catabolism. These findings demonstrate how acetate alters cell metabolism; they also may be useful for the design of aerobic fermentation processes.