Chapter 21 BACTERIA AND ARCHAEA

생물학적 진화의 성공사례인 미생물 지구환경에서의 원핵생물 그림 13. 1A. 질소고정세균

표 어디에나 존재하는 원핵생물

A. Prokaryote Cell Structure All prokaryotes have: cell membrane cytoplasm ribosomes nucleoid region containing DNA Most have a cell wall

Some prokaryotes have: plasmids pili flagella Glycocalyx( 당질피질 ) Slime layer( 느즌함 ) Capsule( 치밀 ) Some prokaryotes form endospores that enable them to survive harsh conditions.

B. Prokaryote Classification 1. Traditional Methods of Classification Based on observable characteristics; groupings do not necessarily reflect evolutionary relationships. Based on Cell Morphology Cocci - have spherical shaped cells

표 13. 2

Bacilli - have rod shaped cells Spirilla - have spiral shaped cells

Based on Staining Characteristics Gram positive (+) bacteria Cell walls have thick peptidoglycan layer; stain purple. Gram negative (-) bacteria Cell walls have thin peptidoglycan layer & an outer membrane( 구성분은 일부 세균의 병원성에 중요 ); stain pink.

Based on Method of Acquiring Carbon & Energy Autotrophs - acquire carbon from inorganic sources (CO 2 ). Heterotrophs - acquire carbon from organic sources (other organisms). Phototrophs - obtain energy from the sun. Chemotrophs - obtain energy by oxidizing inorganic or organic chemicals.

Based on Oxygen Requirements Obligate aerobe - requires oxygen to generate ATP (cellular respiration). Ex. Bacillus Obligate anaerobe - generates ATP without oxygen; oxygen is toxic. Ex. Clostridium tetani Facultative anaerobe - generates ATP with or without oxygen. Ex. Escherichia coli & Salmonella

Based on Habitat Acidophile - prefers a low pH ( ) environment. [hot springs] Halophile - prefers an extremely salty (3.5-30%) environment. [ocean] Thermophile - prefers extreme heat (50 o C-100 o C). [compost heaps]

2. Modern Methods of Classification Based on molecular data; groupings reflect evolutionary relationships. Ribosomal RNA (rRNA) sequences of prokaryotes are compared to identify signature sequences. Signature sequences are short stretches of nucleotides that are unique to certain types of organisms.

Molecular data show Bacteria and Archaea have different: genetic sequences and antibiotic sensitivities (penicillin resistant Archea) cell wall components and membrane lipids No peptidoglycan like in Bacteria numbers of introns (not in bacteria) and repeated genetic sequences cell shapes

Groups of Archaea Euryarchaeota (methanogens, halophiles) Crenarchaeota (thermophiles or moderate habitats Korarchaeota (thermophiles known only from genes)

C. Prokaryote Gene Transfer Genes can be transferred vertically or horizontally. 1. Vertical Gene Transfer Transmission of DNA from a parent cell to daughter cells. Occurs by binary fission.

2. Horizontal Gene Transfer Transmission of DNA from one cell to another cell that is not a daughter cell. Occurs by transformation, transduction, and conjugation. Transformation Cell takes up DNA fragments or plasmids from the environment.

Transduction A virus picks up DNA from one cell and transfers it to another.

Conjugation A sex pilus (cytoplasmic bridge) transfers DNA from one cell to another. Sex pilus

D. Prokaryotes and Humans 1. Harmful effects A few species of bacteria are harmful to man because they are pathogenic. Bacterial infections may be spread by: Air - Legionella pneumophila (causes legionellosis, a form of pneumonia). Arthropods - Yersinia pestis (causes bubonic plague) is transmitted to humans by rat fleas.

Direct Contact - Neisseria gonorrhoeae (causes gonorrhea) is transmitted by sexual contact. Food & Water - Vibrio cholerae (causes cholera); Salmonella enteritidis (causes food poisoning). The use of pathogenic organisms as bioweapons continues to be a major area of concern despite the fact that “germ warfare” was banned by international law in 1925.

2. Beneficial effects Most prokaryotes are beneficial in that they: break down organic wastes & dead organisms. cycle chemical elements (oxygen, nitrogen) between organisms & the environment. are used in the production of food. (vinegar, pickles, sauerkraut, olives, yogurt, cheese)

are used to mass-produce certain non- food items. (vitamins, enzymes, ethanol, acetone, human insulin & blood clotting factors) are used in water and waste treatment. are used in bioremediation. (certain microbes degrade oil, while others remove heavy metals from water)