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 NEGATIVEGRAM 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 Lactobacilli: rod-shaped Enterococci:spherical Spirochaeta: spiral Archaea have many shapes. – spherical, called cocci spiral – spiral, called spirilla or spirochetes

18.4 Bacteria and Archaea Bacteria and archaea have similar structures. flagellum pili plasmid cell wall chromosome plasma membrance This diagram shows the typical structure of a prokaryote. Archaea and bacteria look very similar, although they have important molecular differences. –Flagellum –used for movement –pili –used for attachment

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 during conjugation. Elongating pili form a hallow bridge. Results in genetically different bacterial cells. conjugation bridge 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.