Microbes Bacteria

Microorganisms — bacteria, archaea, viruses, fungi, and protozoa — are the most abundant life forms on Earth. The human body contains approximately 38 trillion bacterial cells (comparable to the number of human cells) — primarily in the gut microbiome. Bacteria were the only life on Earth for 3 billion of the 4 billion years of life's history. They inhabit virtually every environment: volcanic vents (120°C), deep rock (3 km underground), polar ice, clouds, and acidic mine drainage. Bacteria perform essential services: nitrogen fixation (converting atmospheric nitrogen to plant-usable forms — essential for all agriculture); decomposition (breaking down organic matter and recycling nutrients); oxygen production (cyanobacteria); and human health (gut microbiome regulates immunity, mood, metabolism, and digestion). The human gut microbiome contains 3.8 million bacterial genes — 150x more than the human genome. Disruption of the microbiome (by antibiotics, processed food, stress) is linked to obesity, autoimmune disease, depression, and dozens of other conditions.