Simple Life Forms Chapter 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 diameter Three 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 Function Composition 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 supply 2. metabolic waste poisoning 3. consumed by other organisms 4. competition with other microorganisms 5. 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 (CO 2 ) Ex: cyanobacteria, plants, algae 2. Chemoautotrophs – oxidize inorganic substances (H 2 S, NH 3 ) for energy and CO 2 source Ex: Sulfolobus 3. Photoheterotroph – use light energy but must consume organic compounds for carbon source Ex: Rhodobacter 4. Chemoheterotroph – must consume organic compounds for both energy and carbon Ex: Clostridium, protists

Nutrition Modes

Metabolism Obligate aerobes – require oxygen for cellular respiration Facultative anaerobes – can use O 2 but can also grow by fermentation Obligate anaerobes – poisoned by O 2 ; may live through fermentation or carry out anaerobic respiration – use of other substances ( NO 3 or SO 4 )

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 prokaryotes 2. 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 host Rhizobium – N2 converters in roots of legumes Agrobacterium – can be used to transfer DNA in crops – can cause tumors 2. Beta – soil bacteria that recycle nitrogen Nitrosomonas 3. Gamma – some sulfer bacteria; some pathogens Salmonella, E.coli, Vibrio cholera 4. Delta – slime secreting bacteria; attack other bacteria Bdellovibrios 5. 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 syphilis Borrelia 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 water breaks 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