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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 Prokaryotes are the most widespread and abundant organisms on earth. • Over 1 billion types of bacteria • Found everywhere on earth including the air we breathe. • 1 gram of soil contains 5 billion bacterial cells of up to 10,000 different types. 18.4 Bacteria and Archaea Prokaryotes can be divided into two domains 18.4 Bacteria and Archaea Bacteria and Archaea have molecular differences • The cell walls and membranes of bacteria and archaea are chemically different. – Membranes of archaea contain unique lipids that are not found anywhere else on earth. – Bacteria have a chemical called peptidoglycan in their cell walls. GRAM NEGATIVE GRAM POSITIVE 18.4 Bacteria and Archaea • Gram staining identifies bacteria. 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 and archaea are structurally similar but have different molecular characteristics. • Bacteria commonly come in three forms. – rod-shaped, called bacilli – spherical, called cocci spiral – spiral, called spirilla or spirochetes Lactobacilli: rod-shaped Enterococci:spherical • Archaea have many shapes. Spirochaeta: spiral 18.4 Bacteria and Archaea • Bacteria and archaea have similar structures. – Flagellum – used for movement – pili – used for attachment pili plasma 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 can reproduce asexually • Prokaryotes reproduce asexually by a process called binary fission. • Produces a genetically identical daughter cell. 18.4 Bacteria and Archaea Bacteria can reproduce sexually or asexually. • Prokaryotes exchange genes conjugation bridge during conjugation. • Elongating pili form a hallow bridge. • Results in genetically different bacterial cells. TEM; magnification 6000x 18.4 Bacteria and Archaea Bacteria have various strategies for survival. • Bacteria may survive harsh conditions by forming endospores. • Bacteria forms a thick protective layer around the genetic material. • Bacteria will “germinate” and reproduce when conditions become favorable.
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