The amino acid containing indole part is:

Last updated date: 31st Jan 2023
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Hint:We must know that the human intestinal bacteria like Escherichia coli digest Tryptophan - amino acid and it produces indole. So, indole determines microbial ecosystem health in the human gut.

 Complete step by step answer:

Structure of tryptophan:
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Tryptophan is an alpha- amino acid that is used by organisms in the biosynthesis of proteins.
Amino acid Tryptophan consists of an α-amino group, \[-N{H^{3 + }}\]​, an α-carboxylic acid group, \[ - COO\], and a side chain of indole. This composition of tryptophan makes it a non-polar, aromatic amino acid.
 It is an essential amino acid in humans, which means the human body cannot synthesize it and we need to obtain it only from the diet.
 Structure of Indole:
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Indole is an aromatic, crystalline, heterocyclic organic compound with a chemical formula of $C_8H_7N$. Indole is a decomposition product of amino acid – tryptophan. Indole is a bicyclic structured compound, composed of a six-membered benzene ring that is fused to a five-membered nitrogen-containing pyrrole ring.
Biologically, we can prepare indole by specific bacteria as a degradation product of the amino acid tryptophan. It can also be synthesized artificially, at very low concentrations it has flowery smell and so it is used in perfumes.
Indole is a substance that is commonly found in vegetables such as broccoli, sprouts, cabbage, cauliflower, mustard, turnips, etc. It can also be produced in the laboratory. 
So, the amino acid containing the indole part is Tryptophan.
Hence, option A is the correct option.

We can use an indole test to determine the ability of bacteria to digest amino acid tryptophan to form the indole. Tryptophan is digested by tryptophanase to form indole. Indole production is important in the identification of human intestinal bacteria like Enterobacteria.
Indole has an application in prevention of breast cancer, colon cancer, and other types of cancer.