Provide an in-depth explanation of the human microbiome, focusing on its role in health and disease. Discuss recent scientific findings on how gut bacteria influence mental health, metabolism, and immune response, and highlight potential medical applications.

Specifically, delve into:

* **Composition of the Microbiome:** Describe the diverse microorganisms that make up the human microbiome, including bacteria, fungi, and viruses.
* **Gut-Brain Axis:** Explain the connection between the gut microbiome and the brain, and how gut bacteria can influence mental health conditions like anxiety and depression.
* **Metabolic Influence:** Discuss how the microbiome affects metabolism, including nutrient absorption, energy regulation, and the development of obesity and diabetes.
* **Immune System Interaction:** Explain how the microbiome interacts with the immune system, influencing immune responses and the development of autoimmune diseases.
* **Medical Applications:** Discuss potential medical applications of microbiome research, such as fecal microbiota transplantation, probiotics, and personalized microbiome-based therapies. 
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