Prokaryotes : Archaebacteria & Eubacteria

Prokaryotes: Archaebacteria & Eubacteria Characteristics Applications

Classification Domains Prokaryotes Eukaryotes

Prokaryotes Prokaryote – single-celled organisms that lack a true nucleus  Generally referred to as “microbes” or “bugs” Two kingdoms of micro-organisms: Archaeaand Eubacteria  The overwhelming majority of the prokaryotes we deal with on a daily basis are the Eubacteria. • Archaea bacteria: • Usually are found in hostile environments: • e.g. hydrothermal vents, geysers, • oil wells, highly acidic/basic • or alkaline water. • Eubacteria: •  everywhere else including human body

Characteristics of Bacteria • All bacteria are single-celled • They are prokaryotes – their DNA is not compartmentalized • Cell organelles in bacteria are not surrounded by membranes • The DNA is made of a single chromosome • All bacteria reproduce asexually by binary fission

Basic Structure of Bacteria - Size • Microbial Length Unit: • - Micrometer (µm) or ‘micron’ • 10-6meter (1 m = 1,000, 000 µm) • - Nanometer (nm) • 10-9 meter (1 m = 1,000, 000, 000 nm) • Bacterial cells range in size from 10 – 100 µm •  recent discoveries extend this size range to 500 – 1000 µm

Cell structure & components “Typical” eukaryotic cell “Typical” prokaryotic cell

Cell structure & components Cell wall – provides structural support and protection for cell contents Cell membrane – controls the passage of materials into and out of the cell Cytoplasm – contains ribosomes, responsible for the formation of proteins, and DNA, the genetic information of the cell DNA – single stranded chromosome that forms a ring (Plasmid = double stranded) Flagella/Cilia – some bacteria have them, stem from the cell wall and cell membrane functioning as a propellers that help bacteria mobile Bacteria are usually classified by: shape, reaction to being stained, nutrition, and respiration (and not by phylogenetic relationships).

Bacterial Cell Shapes • Coccus • Plural: cocci • spherical cell • Bacillus • Plural: bacilli • rod-like cell • Coccobacillus • Plural: coccobacilli • cells in between round & rod shape • Vibrio • curved cell • Spirillum • Plural: spirilla • rigid, wave-like shaped cell • Spirochete • corkscrew shaped cells • As a population: eg. Cocci • Monococci – live in separate cells • Diplococci – live in pairs • Streptococci – live in linear chains • Staphlococci – live in clusters

Conditions for Growth of Bacteria • Bacteria do not have to remain active in order to survive. They can lie dormant, or inactive, when conditions are not right for growth and other normal activity. When conditions improve, they may become active again, growing and reproducing very rapidly. • The conditions most important for normal activity are:

1. TEMPERATURE: • Many bacteria are most active at fairly warm temperature, about 26 to 38 oC. • Those that cause human infections grow best at 37oC (normal body temperature).Some grow best at temperatures as low as 0oC, mainly in the far north, ocean depths, and high altitudes. • Other bacteria are active at temperatures as high as 85oC, such as those found in hot springs and sewage-thermophiles.

2. MOISTURE • Active bacteria are about 90% water. In dry surroundings, water loss makes the cells inactive. • Dryness over a long period will kill most species.

3. DARKNESS • Most bacteria grow best in the dark. Sunlight (drier/heat) slow down growth. Ultraviolet rays actually kill (affect DNA structure) most bacteria.(used to sterilize hospital operating rooms)

4. FOOD: • Bacteria vary greatly in terms of their food needs; some forms require specific foods. Pathogenic forms need living tissues; other forms are less specific and can live on a wide range of foods.

5. OXYGEN • Some bacteria require oxygen some don’t.

Types of Bacteria – Gram staining Bacteria are further grouped by their cell membrane composition. To classify them, gram staining is used. The method works by checking how the bacteria react to a dye made of crystal violet and iodine. If it is Gram-positive bacteria: - can retain the dye, hence purple - very thick cell membrane • If it is Gram-negative bacteria: • do not stain with Gram stain, hence appears • red/pinkishin color • thinner cell membrane • has a cell wall • large periplasmic space

Metabolism: Respiration Bacteria are also classified based on how they obtain their energy and nutrients! Autotrophs– make their own food Photoautotrophs– similar to photosynthesis in plants, but no 02 is produced; light = energy, organic and inorganic compounds used for nutrients Chemoautotrophs– use inorganic substances to gain energy instead of sunlight; inorganic chemicals = energy, organic and inorganic compounds used for nutrients. E.g. Cyanobacteria (found in hydrothermal vents) Heterotrophs– consume food made by producers Chemoheterotrophs– energy and nutrients from organic compounds (humans are examples of this type of metabolism) Photoheterotrophs– energy from sunlight and use organic compounds for nutrients

Metabolism: Respiration There are specific terminology used to communicate bacteria with various metabolism preference. Since oxygenis common, these terms are based on bacterial: 1) needs for oxygen; 2) toleranceof oxygen; or 3) aversionto oxygen • Obligate aerobes– organisms that can only grow in the presence of 02 E.g. Bacteria that infect the respiratory system of humans; microorganisms that live in the water column of lakes, rivers, and ocean • Facultative anaerobes– organisms that can grow in both in the presence and • the absence of 02. E.g. Bacteria in the human intestines can be exposed to a range of conditions from fully oxygenated (near the stomach) to completely without oxygen (further into the intestines); an example of this type of organism is E. coli. • Obligate anaerobes– can only grow in environments where there is no 02 E.g.deep wounds on skin (hence the awful smell); deep in the soil and sediments; in certain parts of sewage treatment plants

Metabolism: Respiration • How to determine which respiration mode the bacteria exhibit? • ? • ? • ? Thioglycolate broth medium (+ agar + resazurin)

Metabolism: Respiration • How to determine which respiration mode the bacteria exhibit? • Obligated Aerobes – oxygen can only penetrate a short distance into the tube • Obligated Anaerobes – they are sensitive to oxygen so grow away from the surface • Facultative Aerobes – are able to grow in either the presence or the absence of oxygen so grow throughout the tube Thioglycolate broth medium (+ agar + resazurin)

Reproduction: Binary Fission - Bacterial cells grow at an exponential rate when given the right type and amountsof nutrients. - Their mode of reproduction is asexual,by doubling themselves This can translate into a doubling of the population every 20 minutes!

Reproduction: Binary Fission Step 1. Chromosomes duplicate and copies get separated Step 2. Cell elongates and copies of chromosomes move towards the poles Step 3. Cell divides into two daughter cells

Binary Fission vs. Conjugation Binary Fission: asexual process of reproduction and therefore lacks exchange of genetic material. Conjugation: the transfer of genes from one cell to another and therefore increases genetic diversity of a population.

Reproduction: Conjugation Step 1.F+ cell (donor) makes contact with F- cell (recipient) via their tubule pilus Step 2. Conjugation tube form at site of contact bridging the 2 cells Step 3.Single-stranded DNA of the plasmid gets transferred to the recipient cell Step 4.Conjugation tube disconnects. Single-stranded DNA from each cell duplicates making both F+ cells

Uses of Bacteria Bacteria and Diseases: • Not all bacteria cause disease, but some do as part of their metabolism. • These few “bad” bugs give bacteria the group name of “germs” • Pathogen – disease causing agent • - Two general ways a pathogen can operate: •  Break down tissues for food (e.g.Tuberculosis) •  Release toxins that harm the host (e.g.Food poisoning) • - Many bacteria can be killed or kept in check with antibiotics or vaccines •  But problems arise when bacteria become resistantto our drugs. • How would this affect you?

Uses of Bacteria Decomposers: - Bacteria play a critical role in nature by recycling dead organisms  Nutrients in dead organisms can be reused, instead of accumulating  This requires the right mix of the following variables for maximum decomposition to occur: i)Temperature ii)Gas availability for terminal electron accepting (O2 is the best) iii)Water - Widely used by humans to process dead materials as detrivore to get rid of them or to recycle them. e.g. bacteria eating Uranium

Uses of Bacteria • Fixing Nitrogen: • Certain bacteria can convert useless nitrogen to useful nitrogen (fertilizer) • that can be used by other organisms • N2gas (abundance but useless) NH3(ammonia) & other compounds • - This ability to transform nitrogen is called nitrogen fixation • - Nitrogen fixing bacteria are often found in root nodules of legumes (plants) •  these root nodules are functionally equal to fertilizer factory •  plants harbouring these fixing • bacteria grow relatively • faster and healthier.

Prokaryotes : Archaebacteria & Eubacteria