E. coli survives stomach acid primarily by employing a mechanism that utilizes glutamate decarboxylase to neutralize the acidic environment.
Glutamate Decarboxylase System
The main strategy E. coli uses to survive the extremely acidic environment of the stomach involves the glutamate decarboxylase system. This system is crucial for acid resistance. Here’s a breakdown of how it works:
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Glutamate Decarboxylation: E. coli uses the enzyme glutamate decarboxylase to catalyze the conversion of glutamate (an amino acid) into γ-aminobutyric acid (GABA) and carbon dioxide.
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Proton Consumption: This reaction is critical because it consumes protons (H+). Since stomach acid is essentially a high concentration of protons, the removal of protons raises the pH in the immediate vicinity of the bacterium. By consuming H+, the bacterium is essentially neutralizing the acid surrounding it.
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Localized pH Increase: This localized increase in pH allows E. coli to survive long enough to pass through the stomach and reach the more neutral environment of the intestines, where it can colonize.
Other Contributing Factors (Less Direct)
While the glutamate decarboxylase system is the primary mechanism, other factors might contribute to E. coli's survival, although less directly:
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Acid Tolerance Response (ATR): E. coli can develop an adaptive response to mildly acidic conditions. Prior exposure to mild acid stress can trigger the expression of genes that enhance its survival in more extreme acid.
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Stationary Phase Survival: Bacteria in the stationary phase (a period of growth arrest) often exhibit increased resistance to various stresses, including acid.
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Biofilm Formation: Biofilms are structured communities of bacteria that can offer protection against environmental stresses, including acid.
Summary
In short, E. coli relies heavily on the glutamate decarboxylase system to neutralize stomach acid by consuming protons. This allows the bacterium to raise the local pH and survive long enough to reach the intestines.
