Use the following choices to answer the question.a. E. coli growing in glucose broth at 35℃ with O2 for 5 daysb. E. coli growing in glucose broth at 35℃ without O2 for 5 daysc. Both a and bd. Neither a nor bWhich culture produces the most lactic acid?

Ch. 5 - Microbial Metabolism

Tortora - Microbiology: An Introduction 14th Edition

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Ch. 5 - Microbial Metabolism

Problem 7

Chapter 5, Problem 7

Use the following choices to answer the question.
a. E. coli growing in glucose broth at 35℃ with O₂ for 5 days
b. E. coli growing in glucose broth at 35℃ without O₂ for 5 days
c. Both a and b
d. Neither a nor b

Which culture produces the most lactic acid?

Verified step by step guidance

Step 1: Understand the metabolic pathways of E. coli under aerobic and anaerobic conditions. E. coli can perform aerobic respiration when oxygen is present and switch to fermentation or anaerobic respiration when oxygen is absent.

Step 2: Recall that lactic acid is a product of fermentation, specifically lactic acid fermentation, which occurs primarily under anaerobic conditions when oxygen is not available.

Step 3: Analyze the two conditions given: (a) E. coli growing with oxygen (aerobic) and (b) E. coli growing without oxygen (anaerobic). Under aerobic conditions, E. coli primarily uses aerobic respiration, producing less lactic acid.

Step 4: Under anaerobic conditions, E. coli ferments glucose, producing lactic acid among other fermentation products. Therefore, the culture without oxygen is expected to produce more lactic acid.

Step 5: Conclude that the culture described in choice (b) — E. coli growing in glucose broth at 35℃ without O₂ for 5 days — produces the most lactic acid.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Metabolic Pathways in E. coli

E. coli can metabolize glucose through aerobic respiration when oxygen is present, producing mainly CO₂ and water, or switch to fermentation under anaerobic conditions, producing acids like lactic acid. Understanding these pathways helps predict which conditions favor lactic acid production.

Effect of Oxygen on Fermentation

Oxygen availability influences E. coli's metabolism; in aerobic conditions, it prefers respiration, minimizing acid production. Without oxygen, E. coli ferments glucose, generating organic acids such as lactic acid, increasing acid concentration in the culture.

Lactic Acid Production in Bacteria

Lactic acid is a common fermentation product in bacteria under anaerobic conditions. E. coli produces lactic acid via mixed acid fermentation when oxygen is absent, which lowers the pH and accumulates in the medium, indicating anaerobic metabolic activity.

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