BACTERIA

Bacteria are Prokaryotes  Prokaryotes were the initial inhabitants of Earth and today are found almost everywhere  Have no nuclear membrane nor membrane-enclosed organelles  Inside the cell is one large circular strand of DNA or RNA

Bacteria In General:  Are the oldest and most abundant living organisms on Earth  All share basic structures but are diverse in cell shape and nutritional patterns  Affect humans in various ways: cause disease, spoil foods, can be resistant to antibiotics  Fix nitrogen for plants, decompose organic matter, manage hazardous waste, aid animal digestion, help create dairy products

General Structure of Bacteria:

Further Investigation...

Archaebacteria:  Oldest of all life forms  Hypothesized that all life kingdoms descended from ancestors of this group!  Organisms in this taxon possess: -cell walls -single chromosome -unicellular in nature Over half the genes in archaebacteria differ from those of eubacteria

3 Main Orders of Archaebacteria: METHANOGENS -live in oxygen free places, such as animal intestines

3 Main Orders of Archaebacteria: HALOPHILES -salt loving -found in the Dead Sea

3 Main Orders of Archaebacteria: EXTREME THERMOPHILES -live in hot, acidic environments such as hot springs

Eubacteria  Most successful of prokaryotes  Organisms belonging to this taxon possess: -cell walls -single chromosome -unicellular in nature

Basic Bacteria Structure:  Both archaebacteria and eubacteria are classified according to: 1. Cell Shape 2. Gram Stain 3. Nutrition 4. Respiration

1. Cell Shape Bacteria cell shapes come in 3 basic forms: 1. Round – coccus 2. Rod – bacillus 3. Spiral - spirillum

1. Cell Shape  Cocci that live as separate cells = monococci.  Cocci live in pairs = diplococci  Cocci live in linear chains = streptochocci.  Cocci live in grapelike clusters = staphylococci  Bacilli also exists as single, pairs or chains or random attachments  Spiral bacteria exist only as single cells

2. Gram Stain  Gram staining is a differential staining procedure that allows the categorization of bacteria into 2 groups based on their ability to retain a violet stain colour  2 groups: Gram Positive OR Gram Negative (purple colour) (pink colour)

Differences in Gram Staining  Gram-positive organisms are able to retain the crystal violet stain because of the high amount of peptidoglycan in the cell wall.  Gram-positive cell walls typically lack the outer membrane found in Gram-negative bacteria.

3. Nutrition  All cells need energy and a source of carbon for cellular respiration. major energy source light= photosynthetic bacteria Inorganic compounds = chemosynthetic bacteria Photoautotrophs photoheterotrophs chemoautotrophs chemoheterotrophs

3. Nutrition Photoautotrophs: -can synthesize their own organic compounds from sunlight -Cyanobacteria (a.k.a. Blue green algae) -forms blooms in polluted water due to nitrate and phosphate run-off into the water -use up oxygen in lakes/ponds/water source

Bloom of Blue-Green Algae:

3. Nutrition Chemoautotrophs: -obtain energy by breaking apart chemical bonds in inorganic compounds such as hydrogen sulphide and ammonia Chemoheterotrophs: -live everywhere -some are parasites and live off hosts -some are saprobes and consume decomposing hosts

4. Respiration  All living things must carry out cellular respiration to receive energy for life’s functions  Bacteria differ in whether or not they need oxygen  Bacterial respiration falls into 2 basic categories: 1. Aerobes -cellular respiration involves oxygen to produce energy from food that is broken down -obligate aerobes absolutely need oxygen for survival

4. Respiration 2. Anaerobes -bacteria that carry out cellular respiration in an oxygen-free environment -if the presence of oxygen kills these organisms, they are called obligate anaerobes

4. Respiration Example: obligate anaerobe = soil bacterium called Clostridium botulinum that produces toxins that can cause an extreme form of food poisoning called botulism 3. Facultative Anaerobes: can survive in either environment

Bacterial Reproduction Depending on environmental conditions, bacteria can reproduce in a variety of manners: 1. Under favourable conditions 2. Under unfavourable conditions 3. Under extreme conditions

Under Favourable Conditions:  All bacteria use binary fission (asexual reproduction) under ideal conditions  Produce EXACT copies of themselves: parent cell divides into 2 identical offspring  Can divide every minutes  In 12 hours there is 10 to 100 million bacteria!  Genetic mutations occur which increase their diversity and ability to survive  Due to fast reproduction rate bacteria mutate often – 2000/day  If the mutation is favourable then it spreads through the population quickly

Binary Fission

Under Unfavourable Conditions  Will reproduce using conjugation if conditions begin to fail (lack of food, heat, dessication –drying out- or space)  2 bacteria cells connect to each other by long protein bridges called a pilus between them  1 cell transfers a copy of their plasmid (smaller ring of DNA with fewer genes than chromosomes) to the other cell  The bacteria that received this plasmid now has a different genetic make up and this thereby increases their chances of survival  Example: bacteria become resistant to antibiotics

Conjugation

Under Extreme Conditions:  Bacteria form structures called spores – one such is called an endospore  Many gram positive bacteria form these spores  Endospore: bacteria produces a thick wall around DNA and cytoplasm  This enables them to remain dormant for long periods (months) until conditions are once again favourable  So, endospores do not metabolize or reproduce but simply exist until conditions become favourable

Endospores

 Example of Clostridium bacteria with characteristic drumstick-shaped endospore- producing cells.  The dark rod-shaped cells are vegetative cells.  The clear ovals are endospores, and the objects consisting of both dark rod and clear oval are vegetative cells producing endospores. 