30.0 Introduction

1. Simplest Organisms Are Bacteria
1. Resemble First Living Organisms
2. Most Abundant of All Organisms fig 30.1
1. Only organisms to have prokaryotic structure
2. Are vitally important to all ecosystems
3. responsible for first ophotosynthesis and oxygen in atmosphere

30.1 Bacteria are the smallest and most numerous organisms

1. The Prevalence of Bacteria
1. Bacteria Are a Unique Group of Living Organisms
1. Represent the oldest form of life fig 4.11
1. Only representatives of the prokaryotes
2. About 48,000 kinds exist fig 30.2

2. Few major structural differences
3. Species differentiation based on metabolic processes
1. Characterized by growth on certain defined media
2. Activities altered by growth conditions and chemicals

2. The Importance of Bacteria
1. Responsible for creating properties of atmosphere and soils
2. Are metabolically diverse
1. Autotrophic, photosynthetic and chemosynthetic
2. Contribute to world carbon balance
3. Are heterotrophic and break down organic compounds
4. Only a few genera of bacteria are capable of fixing atmospheric nitrogen

3. Involved in industrial processes and chemical syntheses
1. Produce acetic acid, vinegar, amino acids, enzymes
2. Production of various milk products, bread and ethanol
3. Antibiotics derived from bacterial sources

3. Bacteria and Genetic Engineering
1. Non-polluting insect control agents
1. Bacillus thuringiensis attacks insects naturally
2. New strains developed

2. Useful in attempts to understand genetics

2. Prokaryotes Versus Eukaryotes
1. Structural Differences
1. Multicellularity
1. Bacteria are fundamentally single-celled
2. May adhere within matrix, some form filaments
3. Few integrated activities between cells
4. Primitive colonial forms include gliding bacteria fig 30.3

2. Cell size
1. Extremely small individual cell size, 1 micrometer or less
2. Eukaryotes are over 10 times larger

3. Chromosomes
1. Eukaryotes have membrane-bound nucleus
2. Bacterial non-membrane bound DNA is circular and lacks proteins
3. DNA localized in nucleoid

4. Cell division and genetic recombination
1. Bacteria exhibit simple division via binary fission
2. Eukaryote dividion via mitosis with spindles of microtubules
3. True sexual reproduction absent, genetic recombination irregular

5. Internal compartmentalization
1. Eukaryotic metabolic processes enclosed in mitochondria
2. Bacteria lack membrane-bound organelles
3. Enzymes are bound to cell membrane
4. Only organelles present are ribosomes

6. Flagella
1. Bacteria possess simple flagella fig 30.4
2. Composed of single flagellin fiber
3. Lack 9 + 2 structure of eukaryotic flagella and cilia fig 5.30
4. Flagellar motion resembles spinning propeller, not whip-like eukaryotic motion

7. Metabolic diversity
1. Eukaryotic photosynthesis takes place in membrane-bound chloroplasts
2. Eukaryotes exhibit only one form of photosynthesis, releases oxygen
3. Bacterial photosynthesis occurs on membranes
4. Bacteria exhibit several patterns of photosynthesis, aerobic and anaerobic

30.2 Bacterial cell structure is more complex than commonly supposed

1. The Bacterial Surface
1. Cell Wall Structure
1. Polysaccharide network with polypeptide crosslinks
2. Classed as gram-positive or gram-negative fig 30.5
1. Gram-positive composed of polysaccharide network
2. Gram-negative have additional lipopolysaccharide chains
3. Gram-negative are less susceptible to antibiotics

3. May be surrounded by gelatinous capsule

2. General Morphology
1. Cell shape
1. Rod-shaped: Bacilli
2. Spherical: Cocci
3. Spirally coiled: Spirilla

2. Some form stalked structures or filaments that give rise to spores
3. After division individual cells may adhere forming chains
4. Rigid, helical flagella composed of flagellin protein fig 30.6
5. Hairlike pili function in attachment and identification fig 30.4
6. Some form thick-walled endospores
1. Resistant to desiccation
2. Resistant to heat, killed only by extremely high temperatures

2. The Cell Interior
1. Prokaryotic Organization
1. Lack nuclei, do not undergo mitosis, divide by transverse binary fission
2. Lack extensive functional compartmentalization of eukaryotes

2. Common Features
1. Internal membranes
1. Invaginations of the plasma membrane
2. Function in respiration or photosynthesis fig 30.7

2. Nucleoid region
1. Do not possess complex chromosomes of eukaryotes
2. Genes encoded in single double-stranded ring of DNA
3. Located in nucleoid region of cell
4. May also possess small, independently-replicating circles of DNA called plasmids
5. Plasmids contain only a few genes, not necessary for survival

3. Ribosomes
1. Smaller than eukaryotic ribosomes
2. Differ in protein and RNA content
3. Tetracycline and chloramphenicol bind to block protein synthesis

30.3 Bacteria exhibit considerable diversity in both structure and metabolism

1. Bacterial Diversity
1. Not Easily Classified
1. Early classification based on differential stains and Gram stain
2. Other early key characteristics used in classification
1. Photosynthetic or nonphotosynthetic
2. Motile or nonmotile
3. Unicellular or multicellular
4. Formation of spores or dividing by transverse binary fission

3. Description of major phyla tbl 30.1

2. Kinds of Bacteria
1. Diverse in internal chemistry and details of assembly fig 30.8
2. Have adapted to many kinds of environments, some very harsh
1. Invaded waters that are very salty, very acidic/alkaline
2. Very hot locations like hot springs or cold like underneath Antarctic ice

3. Much examination of bacteria in the laboratory
4. Bacteria split into two lines early in their history
1. Domain archaebacteria are confined to extreme environments
2. Domain eubacteria include "common" bacteria, almost all named species

3. Comparing Archaebacteria and Eubacteria
1. Differ in four ways
2. Cell walls
1. Both have cell wall to cover plasma membrane and strengthen cell
2. Eubacteria walls composed of peptidoglycan complex
3. Archaebacteria walls lack peptidoglycan

3. Plasma membranes
1. All have plasma membrane with lipid-bilayer archetecture
2. Each uses different kinds of lipids

4. Gene translation machinery
1. Ribosomal proteins and RNA polymerase of eubacteria different from eukaryotes
2. Those of archaebacteria similar to those of eukaryotes

5. Gene architecture
1. Eubacteria genes not interupted by introns
2. Some genes of archaebacteria have introns

2. Bacterial Variation
1. Bacteria Replicated by Fission Are Identical
1. Forms a large clone of cells
2. Mutation and genetic recombination create variation

2. Mutation
1. One in 200 bacteria will have mutant characteristics fig 30.9
2. Many mutants result from great number of individual cells
3. Rapid multiplication in short time period
1. Increase number with favorable mutations
2. Rapidly changes characteristics of a population

4. Plays important role in genetic diversity
5. Example: Development of antibiotic resistance
1. Strains of Staphylococcus aureus resistant to penicillin and other antibiotics
2. Result from mutation and intense selection in hospital environments
3. Have serious medical implications
4. May be related antibotics given to livestock to increase weight gain

3. Genetic Recombination
1. Transfer of genes via viruses, plasmids, other DNA fragments
2. Examples
1. Rapid transfer of antibiotic resistant plasmids
2. Transfer of pathogenic characteristics among enteric bacteria

3. Bacterial Metabolism
1. Evolved Diverse Ways to Acquire Carbon and Energy
1. Autotrophs obtain carbon from inorganic carbon dioxide
1. Photoautotrophs obtain energy from sunlight
2. Chemoautotrophs obtain energy from inorganic chemicals

2. Heterotrophs obtain some carbon from organic molecules like glucose
1. Photoheterotrophs obtain energy from sunlight
2. Chemoheterotrophs obtain energy from organic molecules

3. Photoautotrophs
1. Carry out photosynthesis with sunlight
2. Build organic molecules from carbon dioxide
3. Cyanobacteria
1. Use chlorophyll a a light-capturing pigment
2. Use water as electron donor
3. Leave oxygen gas as byproduct

4. Other bacteria
1. Use bacteriochlorophyll as pigment
2. Hydrogen sulfide is electron donor
3. Elemental sulfur is byproduct

4. Chemoautotrophs
1. Oxidize inorganic substances
2. Nitrifiers oxidize ammonia or nitrate to form nitrate (taken up by plants)
3. Others oxidize sulfur, hydrogen gas
4. Bacteria around deep-sea vents oxidize hydrogen sulfide

5. Photoheterotrophs
1. The purple nonsulfur bacteria use light
2. Obtain carbon from carbohydrates or alcohols produced by other organisms

6. Chemoheterotrophs
1. Obtain both carbon and energy from organic molecules
2. Include decomposers and most pathogens

2. How Heterotrophs Infect Host Organisms
1. Gram-negative Yersinia produce and secrete large amounts of proteins
1. Proteins lacked either of two signal sequence required to transport across membrane
2. Proteins secreted by new system, type III system

2. Genes for type III system found in other pathogens
1. Genes are more closely related than bacteria that contain them
2. Genes are similar to ones that code for bacteria flagella

3. Function of genes under investigation
1. Some proteins transfer virulence proteins into nearby eukaryotic cells
2. May form flagella-like structure that shoots proteins into host cell
3. Virulence proteins may determine host's response to pathogen

4. Return to Yersinia example
1. Proteins injected into macrophages
2. Disrupt signals to tell macrophages to engulf bacteria

5. Example: Salmonella and Shigella
1. Use type III proteins to enter cytoplasm of eukaryotic cells
2. Protected from host immune system

6. Example: E. coli
1. Alter cytoskeleton of nearby intestinal cells
2. Results in bulge onto which bacterials bind

7. Searching fro ways to disarm bacteria
1. Release virulence proteins before reaching eukaryotic cells
2. Studing target proteins and how they are affected

3. Bacteria as Plant Pathogens
1. Heterophic bacteria cause costly plant diseases
1. Symptoms are generally spots on stems, leaves or fruit
2. Include blights, soft rots and wilts
3. Most pathogens are rod-shaped pseudomonads fig 30.2a

2. Example: Citrus canker
1. Caused by pseudomonad Xanthomonas campestris
2. Introduced from abroad, causes serious economical damage in Florida

30.4 Bacteria are responsible for many human diseases

1. Human Bacteria Diseases
1. Cause Many Human Diseases tbl 30.2
1. Cholera, leprosy, tetanus, bacterial pneumonia, whooping cough, diphtheria
2. Streptococcus causes scarlet and rheumatic fevers, pneumonia, infections fig 30.2b
3. Tuberculosis is a leading cause of human death
4. Staphylococcus cause widespread infections spread through air
5. Many bacterial diseases spread through food or water
6. Insect vectors spread diseases like typhus

2. Tuberculosis
1. One-third of all people infected with Mycobacterium tuberculosis fig 30.10
2. Eight million new cases each year, three million deaths
3. Leading cause of death from a single infectious agent
4. Eradication programs dismantled in U.S. in 1980's
1. Experiencing a dramatic resurgence of the disease
2. Complicated by social factors, declining public health infrastructure
3. Associated with prevalence of HIV

5. Multidrug resistant strains of TB are developing

3. Dental Caries
1. Involves many species of bacteria
2. Dental plaque composed of bacteria and polysaccharide matrix
3. Causes tooth decay and cavities
4. High sugar diets harmful
1. Bacteria convert sugars to lactic acid
2. Acid destroys hard tissue of tooth

5. Control via fluoride by retarding loss of calcium
6. Germ-free animals do not develop decay even with improper diet

4. Sexually Transmitted Diseases
1. STDs caused by bacteria and viruses
1. Viral STDs have no cure
2. Bacterial STDs frequently mutate to drug-resistant strains

2. Gonorrhea
1. Most prevalent communicable disease, caused by Neisseria gonorrhoeae bacterium
2. Transmitted during sexual activities through transfer of body fluids
3. Can spread to eyes (conjunctivitis) and internal organs, cause arthritic meningitis
4. In women, can cause pelvic inflammatory disease, eventual sterility

3. Syphilis
1. Less common as a result of blood-screening procedures and antibiotic treatment
2. Caused by spirochaete bacterium, Treponema palladum
3. Transmitted during intercourse, direct contact with sore
4. Disease progresses in four distinct stages
1. Primary stage characterized by chancre sore, highly infectious stage
2. Secondary stage distinguished by body rash
3. Third stage shows no symptoms, may last years
4. Fourth stage is heart disease, mental deficiency, nerve damage, loss of motor functions, blindness

4. Chlamydia
1. "Silent STD" caused by Chlamydia trachomatis bacterium
1. Has both bacterial and viral characteristics
2. Susceptible to antibiotics like bacterium
3. Depends on host cell to replicate, like virus
4. Is an obligate internal parasite fig 30.11

2. Transmitted via sexual intercourse
3. Women usually do not experience symptoms until infection is established
1. Can cause pelvic inflammatory disease
2. Can lead to sterility, increase risk of acquiring HIV

4. Symptoms in men include watery discharge, burning or itching
5. Tests exist to identify bacteria in discharge
6. Treatment via antibiotics mostly tetracycline, penicillin not effective

5. Sexual activity must be done with certain precautions and extreme care
6. Responsibiliy for protection lies with each individual