Introduction: becoming bacteriocentric -- Guide to habitats -- 1. Ancient hyperthermophiles and thermophilic green nonsulfurs -- Introduction to the archaea -- 2. Methanogens -- 3. Hyperthermophilic archaea -- 4. Halophiles -- 5. Green sulfur bacteria -- Introduction to the proteobacteria -- 6. Alpha proteobacteria -- 7. Beta proteobacteria -- 8. Gamma and delta proteobacteria of non-sulfur-rich environments -- 9. Gamma and delta proteobacteria of sulfur-rich environments -- Introduction to the gram-positive bacteria -- 10. Gram-positive bacteria of foods and drinks -- 11. Gram-positive bacteria of soils and other substrates -- 12. Gram-positive bacteria as symbionts of animals and plants -- Introduction to the cyanobacteria -- 13. Cyanobacteria of aquatic and terrestrial habitats -- 14. Cyanobacteria associations with other organisms -- 15. Bacteroides, gliders, and their relatives -- 16. Spirochetes -- 17. Thermus and Deinococcus -- 18. Planctomycetes and their relatives.