KEY CONCEPT Bacteria and archaea are both single-celled prokaryotes.

1. KEY CONCEPT Bacteria and archaea are both single-celled prokaryotes.

2. Prokaryotes are widespread on Earth. • Prokaryotes can be grouped by their need for oxygen. • obligate anaerobesare poisoned byoxygen • obligate aerobes need oxygen • facultative aerobes can live with or without oxygen Evaluate: Bacteria are often associated with illness. Why is this a misconception?

3. Lactobacilli: rod-shaped Spirochaeta: spiral Enterococci: spherical 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 • Archaea have many shapes.

4. pili plasmamembrance flagellum 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. • plasmid • flagellum • pili • Bacteria and archaea have similar structures.

5. GRAM NEGATIVE GRAM POSITIVE • The amount of peptidoglycan within the cell wall can differ between bacteria • Bacteria and archaea have molecular differences. • Archaea have different lipids entirely

6. Gram-negative bacteria have a thin layer of peptidoglycan and stain red. Gram-positive bacteria have a thicker peptidoglycan layer and stain purple. • stains polymer peptidoglycan • gram-positive stains purple, more peptidoglycan • gram-negative stains pink, less peptidoglycan • Gram staining identifies bacteria.

7. conjugation bridge TEM; magnification 6000x Bacteria have various strategies for survival. • Prokaryotes exchange genes during conjugation. In conjugation genetic material transfers between prokaryotes, producing genetic variation. • Bacteria may survive by forming endospores. Endospores are a specialized cell with a thick, protective cell wall. Endospores can last for centuries. Connect: Why are disinfectants alone not enough to kill all types of bacteria?

8. Prokaryotes provide nutrients to humans and other animals. • Prokaryotes live in digestive systems of animals. • make vitamins • break down food • fill niches Figure: These bacteria, found in human intestines, are beneficial to our health. They produce B vitamins and keep out harmful microbes. (colored SEM; magnification 6300X)

9. yogurt, cheese • Bacteria help ferment many foods. • pickles, sauerkraut • soy sauce, vinegar

10. Prokaryotes play important roles in ecosystems. • Prokaryotes have many functions in ecosystems. • photosynthesize • recycle carbon, nitrogen,hydrogen, sulfur • fix nitrogen Figure: Root nodules of this white clover contain nitrogen-fixing bacteria. Symbiotic bacteria convert nitrogen from the atmosphere (N2) into a form usable by the clover. In return, the plant produces carbohydrates that the bacteria can consume. This SEM (90X) shows root nodules, containing nitrogen-fixing bacteria, of a white clover.

11. Bioremediation uses prokaryotes to break down pollutants. • oil spills • biodegradable materials Figure: Oil spill clean-up, men, cleaning. Sometimes workers will spray bacteria over the contaminated are so the bacteria can digest the chemicals, converting them into harmless or less-harmless compounds.

12. Some bacteria cause disease. • Bacteria cause disease by invading tissues or making toxins. • A toxin is a poison released by an organism. Figure: Clostridium botulinum causes a serious illness called botulism. Food contamination by this bacterium often comes from improper home canning.

13. may colonize new tissues • Normally harmless bacteria can become destructive. Figure: Streptococcus bacteria are commonly found on skin. They are fairly harmless unless they come in contact with tissues they do not normally colonize, such as muscle or fat. This can occur through open wounds.

14. Normally harmless bacteria can become destructive. • immune system may be lowered Apply: Potato salad left out at a picnic is sometimes a source of food poisoning. Which bacterium mentioned above is the most likely culprit? Explain.

15. Antibiotics are used to fight bacterial disease. • Antibiotics may stop bacterial cell wall formation. • Antibiotics do not work on viruses. • Prevention is best method to fight bacterial disease.

16. A bacterium carries genes for antibiotic resistance on a plasmid. A copy of the plasmid is transferred through conjugation. Resistance is quickly spread through many bacteria. Bacteria can evolve resistance to antibiotics. • Bacteria are gaining resistance to antibiotics. • overuse • underuse • misuse • Antibiotics must be used properly. Infer: Why don’t antibiotics affect our bodies’ cells? Connect: How can you use “superbugs” as an example of natural selection?