Prokaryotes- most numerous living organism group

Biology Exploring Life-Chapter 16

Tree of Life- 3 groups

Yellow = Bacteria Green = Archaea Blue= Eukarya

Bacteria vs Archaea

• Environment/habitat-• RNA polymerase-• Presence of introns-• Effects of Antibiotics-• Cell wall structure–Presence of peptidoglycan

What is Peptidoglycan?

• A lattice structure in the bacterial cell wall.– linear chains of alternating amino sugars• N-acetylglucosamine and N-acetylmuramic acid

– short peptide chains of three to five amino acids – The peptide chains form cross-links • resulting in a 3D mesh-like structure.

• Function-– Strength– Counteracts the osmotic pressure of the cytoplasm. – Involved in binary fission during bacterial cell

reproduction.

Peptidoglycan Structure

Basic Bacterial Cell

Bacteria have a basic cell structure that includes a cell wall, plasma membrane, ribosomes, DNA that is not enclosed in a membrane, pili, and flagella for movement.

Classification- Shapes3 main shapes

1. Coccus ,cocci- circular/spherical– Arrangement of cells-– Pairs, chains, clusters, tetrads– Examples- prefix names• Diplococci- 2 cells• Streptococci- chain /string

cells• Staphylococci- cluster-grapelike• Sarcina- tetrad

Gram Stain Examples of Cocci

Staphylococcal infections:blisters, boils, systemic infections

MRSA-

Shapes-2. Bacillus, bacilli- rod-shaped– Various forms -short or long– Single or in chains– Examples-• E. coli• Bacillus subtilus• Lactobacillus vaginalis• Pseudomonas aeruginosa

Gram Stain Gallery of Bacilli

Pseudomonas aeruginosa grows at 42o C.

Hot tub folliculitis

Shapes-3. Spirillum, spirilli- spiral shaped bacteria• Examples- spirochetes– Treponema pallidum- • syphilus- STD

– Borrelia burgdorferi- • lyme disease

Lyme disease caused by the bacterium, Borrelia burgdorferi

Transmitted to humans by bite of infected blacklegged ticks. Most common vectors - Ixodes scapularis ( common deer tick )

has also been carried by the Lone Star tick, Most commonly found in Northeastern and North Central United States.Typical symptoms - fever, headache, fatigue, and a characteristic skin rash called erythema

migrans. Untreated, infection can spread to the heart, the joints and the nervous system.Lyme disease is often diagnosed based on the characteristic rash (bull’s eye) and an

exposure to infected ticksBorrelia burgdorferi is often diagnosed using an enzyme linked immunosorbent assay with

Western blot confirmation

2. Bacterial Cell Wall structures• Different from plants, fungi and protists• Have peptidoglycan• Bacteria are divided into 2 main groups based

on differences in their cell walls.– The amount of peptidoglycan– If they have an outer lipid membrane

• Gram Stain – 1884- Hans Christian Gram

Differential stain • Gram Positive Bacteria• Gram Negative Bacteria

Gram Positive vs Gram Negative Cell walls

Gram Positive Bacteria

• Cell wall consists of a thick outer wall of peptidoglycan

• Stain blue/purple in the gram stain test.• Retain(keep) the initial crystal violet stain

color.• Do not decolorize with alcohol.• Are more sensitive to Penicillin antibiotics.

Gram Negative Bacteria• Two parts to their cell wall– An Inner thin layer of peptidoglycan– An Outer lipid membrane.

• Do not retain (keep) the initial crystal violet stain.

• They are decolorized due to the outer lipid membrane

• They pick up the 2nd stain ( counterstain) safranin and stain pink/red.

Gram Stain Procedure

• See handout for procedure• Refer to handout for results after each step.

Gram Positive vs Gram Negative Cell walls

Importance of the Gram Stain• The key test to differentiate bacteria.• Can be done rapidly- a “STAT” test• Used to divide bacteria into one of two main

groups based on cell wall type.• Used to determine shape (morphology) of

bacteria• Used to presumptively identify the infectious

bacterium.• Used by physicians to prescribe antibiotics

based on type of cell wall.• Key if unable to grow the bacterium

3. Motility- movement• Move toward or away from signals– Food, light, oxygen, toxins

• Flagella-– Anchored in plasma membrane and cell wall.– Bacterial flagella- different from eukaryotes– Different types of flagella- based on numbers and location on

bacterial cell.– bacilli and spirilli are motile– Cocci are nonmotile- do not move

• Pili- allow bacteria to adhere to surfaces and each other.• Slime layers-

Different types of flagella

• monotrichous = single flagellum at one end. amphitrichous = flagella at both ends lophotrichous = tuft of many flagella at one end or both ends. peritrichous = flagella all around the cell

• Motility can be identified in a couple of different ways: – the hanging drop wet mount- look for directional movement. – Semi-solid motility agar- stab and incubate overnight.

4. Environment

• Aerobic bacteria- need oxygen to survive.• Anaerobic bacteria- live without oxygen,

strict anaerobes- cannot tolerate oxygen.• Most bacteria can live in both environments-– Facultative anaerobes.

• Binary fission- clones-results in two identical cells– Mutations can occur in copying of DNA

• Simpler than mitosis• Rapid, continuous, ~ every 20 minutes, exponential growth-

1,2,4,8,16,32. • Refrigeration slows down rate of reproduction

Reproduction in Bacteria

Bacterial Growth Curve- 4 stages- Typical S curve.

1. lag phase- start up2. log-logarithmic phase- rapid exponential growth3. stationary phase- limiting factors( food, water, space, waste)

– Carrying capacity =most numbers of population due to limiting factors– Death rate= birth rate.

4. Death phase.Review Pg 376- Question # 18.

3 methods of Genetic Variation

• Transformation- bacteria takes up DNA from environment

• Conjugation- 2 bacterial cell join and transfer genetic material- plasmids

• Transduction- when viruses (bacteriophage) infect bacteria with their genes.

Transformation and Conjugation

Transduction

Endospores

• Special resting cells.– Thick protective coat – surrounding the chromosome, very resistant.

• Survival in unfavorable conditions– Lack of water, nutrients, heat, cold, toxins– Can last for years.– Absorb water when favorable environment and grow

again.

• Example- Bacillus anthracis- anthrax

Modes of Nutrition• How organisms obtain energy and carbon atoms. • Energy by photosynthesis –light - use prefix photo. • Energy from chemical sources – inorganic or organic- use prefix chemo. • Autotrophs obtain carbon atoms from carbon dioxide. • Heterotrophs obtain carbon from existing organic molecules (such as those in

food). • Bacteria- most numerous organisms- found in all 4 modes• Photoautotrophs- carry out photosynthesis- plants, plant like protists, and

photosynthetic bacteria• Chemoautotrophs use carbon dioxide as a carbon source, but they extract energy

from inorganic substances such as hydrogen sulfide or ammonia. All chemoautotrophs are prokaryotes.

• Photoheterotrophs use light energy to make ATP but obtain their carbon in organic form. This mode of nutrition is only found in certain prokaryotes.

• Chemoheterotrophs consume organic molecules for both energy and carbon. Found in many bacteria, animal and fungi like protists, fungi, and animals.We are chemoheterotrophs.

4 categories of nutrition

• Plants, algae, prokaryotes

• Prokaryotes only

• Prokaryotes only

• Prokaryotes, animal and fungus like protists, all fungi, all animals

Cyanobacterium

• Photoautotrophs• Ancient• Oxygen released in photosynthesis• Oxygen revolution– Extinction of some – Survival in anaerobic environments– Adaptation for organisms that can survive in oxygen-

aerobic organisms- many prokaryotes, nearly all eukaryotes. Oxygen used to make most amounts of ATP- energy.

Important functions of prokaryotes 16.3

• Chemical recycling • Decomposers- break down organic waste and

dead organisms in environment.– Returns carbon to atmosphere as CO2.- carbon

cycle

• Nitrogen cycle- nitrogen fixing bacteria- N2-NO3 and ammonium to be used by plants.

Bioremediation

• Use of prokaryotes to remove pollutants from water, air, and soil.

• Sewage treatment• Pseudomonas sp.- oil degradation on beaches.• Thiobacillus- lives in acidic mine environments,

removes lead and mercury in mine runoff.• Making vitamins and antibiotics• Genetic engineering- making protein products.

Pathogenic Bacteria

• Pathogens- disease causing microorganisms.• Body defenses- examples-– Skin, normal biotic flora

• Bacteria poisons- toxins– 2 types

• Secreted by the bacterial cell- exotoxin– Food poisoning- Clostridium botulinum – Staphylococci

• Toxin is part of cell wall– Drop in blood pressure-shock– Salmonella food poisoning

Defenses against disease

• Washing hands• Care in food prep.• Water control• Good hygiene• Vaccines• Antibiotics– Major Health Concern- resistance of bacteria-

mutations and genetic variation