Which phylum includes Gram-negative, obligately anaerobic bacteria that are dominant in the human gut?

Question

BlackTom AI · Accepted Answer

Here is a breakdown of each answer choice and the reasoning behind why it is correct or incorrect.
Option 1: Firmicutes. This phylum is known for many Gram-positive bacteria with thick peptidoglycan cell walls and typically many are obligate or facultative anaerobes, but they are not the dominant Gram-negative group in the human gut. The question specifies Gram-negative organisms, which points away from Firmicutes, so this option does not fit the description.
Option 2: Proteobacteria. This is a major phylum consisting largely of Gram-negative bacteria, including many facultative and strictly anaerobic species in various environments. However, in the context of the human gut microbiome, Proteobacteria are not the dominant Gram-negative group; they are often present in lower abundance and can bloom under dysbiosis. Therefore, this choice does not match the phrasing of “dominant in the human gut.”
Option 3: Bacteroidetes. This phylum comprises Gram-negative, obligately anaerobic bacteria and is one of the principal dominant groups in the adult human colon. Members such as Bacteroides are well-known for their prominence in the gut microbiota and their strict anaerobic metabolism, aligning perfectly with the description given in the question. This makes the option consistent with the stated characteristics.
Option 4: Actinobacteria. While Actinobacteria include notable Gram-positive organisms and some gut residents, they are not primarily Gram-negative, nor are they described as the dominant Gram-negative group in the human gut. Therefore, this selection mischaracterizes the key features specified in the prompt.
In summary, option 3 best matches the specific combination of Gram-negative status, obligate anaerobiosis, and dominance in the human gut, whereas the other options do not satisfy all of these criteria.

MIMI2002 (ND) Tute-shop 1 EFT Quiz

Which phylum includes Gram-negative, obligately anaerobic bacteria that are dominant in the human gut?

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