Question

Acetyl-CoA synthase genes occur in phyla, Deltaproteobacteria and Chlorofelxi. What evidence would you suggest to support that these organisms are anaerobic?

Answer 1

Growth kinetics in the presence and absence of oxygen can be used to decipher between anaerobic and aerobic bacteria. If Deltaproteobacteria and Chlorofelxi are anaerobic, their growth would be retarded or would not survive in the presence of oxygen. On the other hand, if the absence of oxygen supports the growth of Deltaproteobacteria and Chlorofelxi that means, both the organisms are anaerobic.

Answer 2

Deltaproteobacteria and Chloroflexi) are anaerobic, you could provide the following evidence:

1. Biochemical Pathway Evidence:

• Acetyl-CoA synthase is a key enzyme in the Wood-Ljungdahl pathway, a metabolic pathway used by strict anaerobes for carbon fixation and energy production. This pathway is typically found in organisms that thrive in anaerobic environments (e.g., methanogens, acetogens).

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2. Genomic Context:

• The presence of other genes associated with anaerobic metabolism (e.g., hydrogenases, ferredoxin-dependent redox systems) in the same genomes would support anaerobic lifestyles.

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3. Physiological Studies:

• Laboratory experiments showing that these organisms grow only (or optimally) in the absence of oxygen.

• Detection of anaerobic metabolic byproducts (e.g., acetate, methane, or hydrogen sulfide) in cultures.

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4. Ecological Habitat:

• Evidence that these organisms are found in anaerobic environments (e.g., deep sediments, hydrothermal vents, or the guts of animals).

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5. Evolutionary Conservation:

• Phylogenetic analysis showing that the Acetyl-CoA synthase genes in these groups are closely related to those in other known anaerobic lineages.

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6. Oxygen Sensitivity Experiments:

• Demonstration that the enzyme (or organism) is inactivated or damaged by exposure to oxygen, indicating adaptation to anaerobic conditions.

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Key Point:

The Wood-Ljungdahl pathway (in which Acetyl-CoA synthase operates) is a hallmark of anaerobic metabolism, so its presence strongly suggests an anaerobic lifestyle.