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18.4 Bacteria and Archaea KEY CONCEPT Bacteria and archaea are both single-celled prokaryotes. 18.4 Bacteria and Archaea Prokaryotes are widespread on Earth. • Prokaryotes can be grouped by their need for oxygen. – obligate anaerobes are poisoned by oxygen – obligate aerobes need oxygen – facultative aerobes can live with or without oxygen 18.4 Bacteria and Archaea Bacteria and archaea are structurally similar but have different molecular characteristics. • Bacteria commonly come in three forms. – rod-shaped, called bacilli – spiral, called spirilla or spirochetes – spherical, called cocci Lactobacilli: rod-shaped Spirochaeta: spiral • Archaea have many shapes. Enterococci: spherical 18.4 Bacteria and Archaea • Bacteria and archaea have similar structures. – plasmid – flagellum pili plasma – pili membrance chromosome cell wall plasmid This diagram shows the typical structure of a prokaryote. Archaea and bacteria look very similar, although they have important molecular differences. flagellum 18.4 Bacteria and Archaea • Bacteria and archaea have molecular differences. – The amount of peptidoglycan within the cell wall can differ between bacteria GRAM NEGATIVE GRAM POSITIVE – Archaea have different lipids entirely 18.4 Bacteria and Archaea • Gram staining identifies bacteria. – stains polymer peptidoglycan – gram-positive stains purple, more peptidoglycan – gram-negative stains pink, less peptidoglycan Gram-negative bacteria have a thin layer of peptidoglycan and stain red. Gram-positive bacteria have a thicker peptidoglycan layer and stain purple. 18.4 Bacteria and Archaea Bacteria have various strategies for survival. • Prokaryotes exchange genes conjugation bridge during conjugation. • Bacteria may survive by forming endospores. TEM; magnification 6000x