Question

Even though Pseudomonas aeruginosa and Enterococcus faecalis usually grow harmlessly, they can cause disease. Because these bacteria use the Entner- Doudoroff pathway instead of glycolysis to catabolize glucose, investigators can use clinical tests that provide evidence of the Entner-Doudoroff pathway to identify the presence of these potential pathogens. Suppose you were able to identify the presence of any specific organic compound. Name a substrate molecule you would find in Pseudomonas and Enterococcus cells but not in human cells.

Short answer

A substrate molecule that would be found in Pseudomonas and Enterococcus cells but not in human cells is either 6-phosphogluconate (6PG) or KDPG (2-keto-3-deoxy-6-phosphogluconate). These molecules are unique to the Entner-Doudoroff pathway and are not found in human glycolysis.

Step-by-step solution

Understanding Glycolysis and the Entner-Doudoroff Pathway

Glycolysis is a universal pathway present in all organisms, from yeast to mammals, for the breakdown of glucose into pyruvate, which the cell can use to produce ATP. In contrast, the Entner-Doudoroff pathway, used by some bacteria and archaea, is an alternate series of reactions that also apprehend glucose and convert it into pyruvate. Though both pathways result in pyruvate, the intermediate molecules involved differ.

Identifying Unique Molecules in the Entner-Doudoroff Pathway

In the Entner-Doudoroff pathway, two unique molecules that are not typically found in the glycolytic pathway are 6-phosphogluconate (6PG) and KDPG (2-keto-3-deoxy-6-phosphogluconate). Either of these molecules can be the substrate molecule that the problem is asking for.

Dismissing Non-Unique Molecules

Recognize that glucose-6-phosphate (G6P) could also be thought as a candidate, but it must be eliminated as a possibility because it is an intermediate in both the Entner-Doudoroff pathway and human glycolysis, therefore, it would be found in human cells as well.

Key concepts

Pseudomonas aeruginosa

Pseudomonas aeruginosa is a common gram-negative, rod-shaped bacterium that is known for its versatility and adaptability. It is found in many environments, including soil, water, and human-made environments like hospitals. While it can be a harmless organism in its natural settings, in hospitals, it can cause serious infections, particularly in patients with weakened immune systems. It can infect different parts of the body, causing issues such as respiratory infections, urinary tract infections, and sepsis.
This bacterium is notorious for its resistance to antibiotics, which makes infections challenging to treat. Understanding its unique metabolic pathways, such as the Entner-Doudoroff pathway, is crucial not only for accurate clinical identification but also for targeting potential vulnerabilities in its metabolism for novel treatments.

Enterococcus faecalis

Enterococcus faecalis is a gram-positive, commensal bacterium that is commonly found in the human gut. Despite its presence as a normal part of the intestinal flora, it can become opportunistic and cause infections if it spreads to other parts of the body. Infections caused by E. faecalis can include urinary tract infections, endocarditis, and bacteremia, often occurring in hospital settings.
E. faecalis is known for its ability to acquire resistance to antibiotics, making it a concern for patients with compromised immune systems. The unique features of its metabolic processes, including the use of the Entner-Doudoroff pathway, provide important clues for its identification and the development of specific therapies aimed at controlling its growth.

Bacterial metabolic pathways

Bacteria possess a myriad of metabolic pathways that allow them to utilize various sources of energy and carbon. These pathways are essential for their survival, growth, and the ability to adapt to different environments. The major metabolic pathways in bacteria include glycolysis, the citric acid cycle, and the oxidative phosphorylation pathway. However, some bacteria have alternative pathways, such as the Entner-Doudoroff pathway.
The Entner-Doudoroff pathway is an alternative to glycolysis and is not found in human cells. This pathway yields ATP, NADPH, and pyruvate using unique intermediates like 6-phosphogluconate and KDPG. Understanding these unique pathways is crucial for studying bacterial ecology and for developing antimicrobial strategies.

Clinical identification of pathogens

The clinical identification of pathogens is a critical aspect of diagnosing and treating infectious diseases. Traditional methods of identification include culture techniques, microscopy, and biochemical tests. Contemporary methods also involve molecular diagnostics such as PCR and genomic sequencing. Metabolic pathways play a significant role in these identifications. Detecting the presence of specific metabolites or enzymes unique to certain pathogens, like those in the Entner-Doudoroff pathway, can help pinpoint the cause of an infection.
In the case of Pseudomonas aeruginosa and Enterococcus faecalis, identification can be assisted by finding substrates like 6-phosphogluconate or KDPG, which wouldn't be present in human cells. These metabolic markers can enhance the accuracy of identifying these organisms and allow for targeted antibiotic therapy.