Phylum Firmicutes: BAL-Fall 2026-General Microbiology

Overview of Phylum Firmicutes

• Gut Microbiota: Firmicutes and Bacteroidetes constitute over $90\%$ of human gut microbiota. The Firmicutes/Bacteroidetes ratio serves as a marker for obesity and gut dysbiosis.

• Taxonomy: Formally named Phylum Bacillota; includes both bacilli and cocci cell morphologies.

General Characteristics of Bacillota

• Genetics & Staining: Mostly Gram-positive with low G+C DNA content (unlike high G+C Actinobacteria).

• Resilience: Over $274$ genera; many produce endospores resistant to desiccation.

• Significance: Includes notable human pathogens and organisms causing spoilage in canned food, beer, wine, and cider.