Chapter 20 BACTERIA AND ARCHAEA

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

plasmids pili flagella glycocalyx endospores

crystal violet (iodine helps to retain the dye)  safranin

1. Glycocalyx is composed of proteins/polysaccharides 2. A loose glycocalyx is a slime layer, a firm glycocalyx is a capsule 3. Attachment to surface, resistance to drying, and protection from host immune system

Prokaryote Classification Traditional Methods of Classification 1) Based on observable characteristics 2) groupings do not necessarily reflect evolutionary relationships 3) Based on Cell Morphology

Bacilli - have rod shaped cells Spirilla - have spiral shaped cells Cocci - have spherical shaped cells Based on Morphology

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

 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 Method of Acquiring Carbon & Energy

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

Based on Habitat

Modern Methods of Classification 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.

Epulopiscium fishelsoni, discovered in 1993 in red sea in a large fish intestine Use PCR to amplify rRNA

genetic sequences and antibiotic sensitivities cell wall components and membrane lipids numbers of introns and repeated genetic sequences cell shapes Molecular Data Show Bacteria and Archaea Are Different

Weird shape of Archaea shows their different cellular organization and composition

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

Prokaryote Gene Transfer Vertical Gene Transfer Transmission of DNA from a parent cell to daughter cells. Occurs by binary fission.

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

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

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

Horozontal gene transfer is partly responsible for the spread of antibiotic resistance genes among bacteria

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 淋巴腺鼠疫 ) is transmitted to humans by rat fleas. Prokaryotes and Humans

 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.

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) Beneficial Effects

 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)