The abundance of tryptophan in E. coli: what happens?

E. coli is a bacterium that can be found in soil, water, and some foods. It is also present in the intestinal tract of animals and humans as a natural part of the microbiome. This bacterium has been widely studied because of its significance in biotechnology and medicine. One of the most widely researched aspects of E. coli is its ability to produce amino acids, including tryptophan. In this article, we will explore what happens when there is an abundance of tryptophan in E. coli and the mechanisms underlying these events.

Tryptophan biosynthesis in E. coli

E. coli is known for its ability to produce tryptophan, one of the essential amino acids that humans need in their diet. Tryptophan biosynthesis occurs in several steps, with multiple enzymes involved in each reaction. The first step of the pathway is the conversion of the amino acid chorismate to anthranilate through the enzyme anthranilate synthase. This step is followed by several reactions leading to the formation of tryptophan.

The role of the trp operon

The trp operon is a set of five genes in E. coli that are responsible for tryptophan biosynthesis. These genes are regulated by a mechanism called attenuation, which allows the bacterium to produce only the necessary amount of tryptophan. The trp operon contains a leader sequence that can fold into two alternative structures, depending on the level of tryptophan in the cell. When tryptophan is scarce, the ribosome stalls at a region of the leader sequence, which masks a transcription terminator site. This allows the RNA polymerase to transcribe the trp genes, leading to tryptophan biosynthesis. When tryptophan is abundant, the ribosome proceeds through the leader sequence and reaches the terminator site, terminating transcription and stopping tryptophan production.

The consequences of tryptophan abundance

When there is an overabundance of tryptophan in E. coli, several processes occur to regulate its metabolism. Excess tryptophan is converted to its degradation compound, indole, by the enzyme tryptophanase. Indole is a signaling molecule that E. coli uses to sense its environment and communicate with other bacterial cells. Additionally, tryptophan abundance leads to the inhibition of other biosynthetic pathways, as the cell has enough tryptophan and no longer needs to produce it. This feedback inhibition helps to prevent the waste of cellular resources on unnecessary biosynthetic reactions.


The abundance of tryptophan in E. coli triggers a variety of mechanisms to regulate tryptophan metabolism and prevent unnecessary biosynthesis. The trp operon and the attenuation mechanism allow the bacterium to regulate the tryptophan biosynthesis pathway and produce only the necessary amount of the amino acid. Excess tryptophan is converted to indole, which can act as a signaling molecule, while feedback inhibition prevents the waste of cellular resources. Understanding the consequences of tryptophan abundance in E. coli is crucial for understanding the metabolism of this bacterium and its applications in biotechnology and medicine.

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