Simple Life FormsChapter 27 Prokaryotes

Numbers

• Prokaryotes have a collective biomass ten times that of all eukaryotes

• Number in a handful of soil is greater than the number of people who ever lived

• Wealth of adaptations has contributed to dominant success

• Can live in places too acidic, too salty, too cold, or too hot.

Structure and Function

• Typically unicellular• 1-5 micrometers in diameterThree common shapes:

1. Spherical ( cocci)2. Rods (bacilli)3. Spirals

Structure and Function

• Integral feature of prokaryotes is their cell wall and its composition

- functions: maintain shape, physical protection, osmotic control (more hypotonic than hypertonic – severe water loss impedes reproduction)

- covered by a capsule either of polysaccharide or protein makeup- fimbriae – numerous, tiny appendages that allow attachment to host- pili – longer hair-like appendage (conjugation)

Structure and FunctionComposition of cell wall:

a. Peptidoglycan – modified sugar polymers cross linked by polypeptides

Ex: gram positive – purple stain Staphylococcus

b. Lipopolysaccharides – carbohydrate bonded to lipid molecules

Ex: gram negative – pink stain ( more toxic and resistant)

E. coli, Salmonella

Motility

• Flagella is mainly mechanism of movement

• Can covered entire surface or be concentrated on one or both ends

• Random movement• Taxis – movement toward or

away from a stimulus

Internal & Genomic Organization

• Lack organelles like eukaryotes, but contain specialized membranes (respiratory & thylakoid)

• Nucleoid region of cell contains a chromosome or circular DNA , and additional DNA plasmids

• Plasmids replicate independently of main chromosome, and cell can survive without its plasmids

Reproduction

• Reproduction asexually through binary fission- can divide every 1 – 3 hours- some as fast as 20 minutes

• Natural limitations of reproductive growth:1. exhausted nutrient supply2. metabolic waste poisoning3. consumed by other organisms4. competition with other microorganisms5. antibiotic interaction

Adaptation• Rapid reproduction leads to wide range

of mutations that can develop- Mutations provide variability and

greater fitness to certain environments- model for natural selection

Endospores – form of resistant cell when essential nutrients are lacking- very tolerant of harsh conditions

• Horizontal gene transfer – exchange of plasmid genes between cells; incorporates into another prokaryote genome

- rapid facilitation of evolution

Nutritional Diversity• Prokaryotes have 4 modes of nutrition:

1. Photoautotrophs – use light energy to synthesis organic compounds (CO2)

Ex: cyanobacteria, plants, algae2. Chemoautotrophs – oxidize inorganic substances (H2S, NH3)

for energy and CO2 sourceEx: Sulfolobus3. Photoheterotroph – use light energy but must consume

organic compounds for carbon sourceEx: Rhodobacter4. Chemoheterotroph – must consume organic compounds for

both energy and carbonEx: Clostridium, protists

Nutrition Modes

Metabolism

• Obligate aerobes – require oxygen for cellular respiration

• Facultative anaerobes – can use O2 but can also grow by fermentation

• Obligate anaerobes – poisoned by O2; may live through fermentation or carry out anaerobic respiration – use of other substances ( NO3 or SO4)

Metabolism• Nitrogen is essential for production of amino acids and nucleic

acids• Nitrogen fixation – converts atmospheric nitrogen into ammonia

(NH3)- fixed nitrogen used to produce amino and nucleic acids

• Metabolic cooperation – occurs between specialized cells in colonies

- allows to metabolic activities to take place at same time that could not be done by single cell

- Biofilms- signal molecules are secreted to recruit new cells to increase colony growth

- Sulfate consuming bacteria and methane consuming archaea cooperate in which product of synthesis and waste are energy source for the other

Molecular Systematics

• Use of small subunit ribosomal RNA has revealed diversity from common ancestor between some bacteria and new domain known as Archaea

• Two lessons have been recognized from systematics

1. Immense genetic diversity of prokaryotes2. Horizontal gene transfer plays a significant role in evolution of prokaryotes

Archaea• Combined characteristics from both prokaryotes and eukaryotes• Extremophiles – lovers of extreme conditions

1. Thermophiles – thrive in extremely hot environments Ex: Sulfolobus- sulfer rich volcanic springs, Pyrolobus fumarii – hydrothermal vent in Mid Atlantic

ridge

2. Halophiles – live in highly saline environments; some require for existence; some tolerant

3. Methanogens – use CO2 to oxidize H2, release methane ( CH4) as waste product; live in swamps or marches; anaerobic; can live in intestines of cattle, termites

-serve as decomposers in sewage treatment plants

Major Bacterial Groups• Proteobacteria – diverse group of gram negative bacteria; 5 subgroups

1. Alpha – associated with eukaryotic hostRhizobium – N2 converters in roots of legumesAgrobacterium – can be used to transfer DNA in crops – can

cause tumors2. Beta – soil bacteria that recycle nitrogen

Nitrosomonas3. Gamma – some sulfer bacteria; some pathogens

Salmonella, E.coli, Vibrio cholera4. Delta – slime secreting bacteria; attack other bacteria

Bdellovibrios5. Epsilon – pathogens to humans and animals

Campylobacter – blood poisoning and intestinal inflammation

Helicobacter – stomach ulcers

Major Bacterial Groups

• Chlamydias – parasites of animal cells; gram negative; most common STD in U.S.

• Spirochetes – free living; pathogenic Treponema pallidum – causes syphilisBorrelia burgdorferi - Lyme disease

• Cyanobacteria – one of the oldest known prokaryotes; N2 fixers; only prokaryote with plant-like oxygen generating photosynthesis; Abundant in water

Major Bacterial Groups

• Gram positive – large diversity; free living species; colonial or solitary;

*actinomycetes – can cause tuberculosis and leprosy; some just soil decomposers

*Streptomyces – source of antibiotics*Bacillus anthracis- anthrax*Clostridium botulinum – botulism*Staphylococcus- Staph – Wash Your Hands*Streptococcus – strep throat

Prokaryote Role in Biosphere

• Most important role is as a decomposer for breaking down corpses, dead vegetation, and waste products

• Play Symbiotic role with eukaryotes- Host is larger organism- Symbiont – smaller one

*Mutualism*Commensalism*Parasitism

Harmful vs. Beneficial

• Best known are the pathogens, but they represent a small fraction of all prokaryotes

• 2 to 3 million people die from tuberculosis a year• Lyme disease is the most widespread pest disease in U.S.• Cholera – dangerous diarrheal disease• Salmonella – food poisoning• Horizontal gene transfer can cause a harmless strain to

become pathogenic• E. coli 0157.H7 from contaminated beef

• Anthrax, C. botulinum, Yersinia pestis – weapons of bioterrorism

Harmful vs. Beneficial• Biotechnology of gene cloning with E. coli• Agrobacterium tumefaciens produces transgenic plants• Bioremediation – cleaning up pollutants from soil, air,

and waterbreaks down sewage, radioactive waste or cleaning

up oil spills• Mining industry uses prokaryotes to recover metals

from ore – gold and copper • Genetic engineering uses prokaryotes to produce

vitamins, antibiotics, and hormones