What are the key topics extracted from the page on bacteria, along with a simple two-line definition for each?

Here are the key topics extracted from the page, each with a simple two-line definition: 1. **Diversity in Bacteria and Ecology** Prokaryotes are ancient, widespread organisms classified into 16 phyla by Margulis and Schwartz. They adapt to almost every environment on Earth, from extreme habitats to soil and petroleum deposits. 2. **Omnibacteria** Rigid, rod-shaped, Gram-negative bacteria that usually require oxygen and do not produce spores. They often use flagella to move around, and common examples include *Escherichia coli* and vibrios. 3. **Cyanobacteria** Photosynthetic bacteria containing chlorophyll-a that produce oxygen and fix nitrogen in special cells called heterocysts. They play a major environmental role and often form colorful blooms on polluted water or soil surfaces. 4. **Mycoplasmas and Spiroplasmas** Unique bacteria that completely lack cell walls, making them naturally resistant to antibiotics like penicillin. They cause diseases in both humans (such as pneumonia) and plants (such as yellowing disease in coconuts). 5. **Spirochaetes** Long, spiral-shaped, Gram-negative bacteria equipped with multiple flagella for movement. An important example is *Treponema*, which causes the sexually transmitted disease syphilis. 6. **Pseudomonads** Straight or curved rod-shaped, Gram-negative bacteria found commonly in soil and water. They break down organic matter, play a role in denitrification, and can act as plant pathogens.