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Ch 27: Prokaryotes - Bacteria and Archaea
Prokaryotes are divided into two domains bacteria and archaea thrive in diverse habitats including places too acidic, salty, cold, or hot for most other organisms Most are microscopic but what they lack in size they make up for in numbers For example: more in a handful of fertile soil than the number of people who have ever lived Great Salt Lake – pink color from living prokaryotes; survive in 32% salt
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Prokaryotes Single cell Very small
Some form colonies Very small 0.5–5 µm (10-20 times smaller than Eukaryotes) Lacks nucleus and most other membrane bound organelles Reproduce very quickly Asexual binary fission Genetic recombination variety of shapes spheres (cocci) rods (bacilli) spirals Cell wall More structural & functional characteristics in (Ch.27)
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Bacilli Rod shaped Usually solitary Sometimes chains Example: E. coli
streptobacilli
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Cocci Spherical Clumps or clusters (like grapes)
E.g. Staphylococcus aureus Streptococci – chains of spheres Diplococci – pairs of spheres E.g. Neisseria gonnorheae
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Streptococcus 1
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Streptococcus 2
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Diplococcus 1
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Diplococcus 2
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Spiral prokaryotes Spirilla – spiral shaped Spirochaetes
With external flagella Variable lengths Spirochaetes Internal flagella Corkscrew-like Boring action E.g. Treponema pallidum (Syphilis)
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Cell-Surface Structures
Cell wall is important maintains cell shape protects the cell prevents it from bursting in a hypotonic environment Eukaryote cell walls are made of cellulose or chitin Bacterial cell walls contain peptidoglycan network of sugar polymers cross-linked by polypeptides Archaea cell walls polysaccharides and proteins but lack peptidoglycan
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Scientists use the Gram stain to classify bacteria by cell wall composition
Counter stains to differentiate between cell wall characteristics Gram-positive bacteria simpler walls with a large amount of peptidoglycan Gram-negative bacteria less peptidoglycan and an outer membrane that can be toxic Gram-positive bacteria 10 m Gram-negative
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Gram positive bacteria
Thick layer of peptidoglycans Retains crystal violet Doesn’t wash out Masks red safranin Stains dark purple or blue-black
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Gram negative bacteria
Outer membrane Peptido- glycan layer Plasma membrane Cell wall Carbohydrate portion of lipopolysaccharide (b) Gram-negative bacteria: crystal violet is easily rinsed away, revealing red dye. Thin sandwiched layer of peptidoglycans Rinses away crystal violet Stains pink or red
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Extra capsule covers many prokaryotes
Bacterial cell wall capsule Tonsil cell 200 nm Extra capsule covers many prokaryotes polysaccharide or protein layer Some also have fimbriae stick to substrate or other individuals in a colony Pili (or sex pili) longer than fimbriae allow prokaryotes to exchange DNA Fimbriae 1 m
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Diverse nutritional and metabolic adaptations have evolved in prokaryotes
Prokaryotes can be categorized by how they obtain energy and carbon Phototrophs obtain energy from light Chemotrophs obtain energy from chemicals Autotrophs require CO2 as a carbon source Heterotrophs require an organic nutrient to make organic compounds Energy and carbon sources are combined to give four major modes of nutrition
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The Role of Oxygen in Metabolism
Prokaryotic metabolism varies with respect to O2 Obligate aerobes require O2 for cellular respiration Obligate anaerobes are poisoned by O2 and use fermentation or anaerobic respiration Facultative anaerobes can survive with or without O2
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Nitrogen Metabolism Nitrogen is essential for the production of amino acids and nucleic acids – nitrogen fixation some prokaryotes convert atmospheric nitrogen (N2) to ammonia (NH3) Some cooperate between cells of a colony allows them to use environmental resources they could not use as individual cells E.g. cyanobacterium Anabaena, photosynthetic cells and nitrogen-fixing cells called heterocysts (or heterocytes) exchange metabolic products Photosynthetic cells Heterocyst 20 m
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Molecular systematics led to the splitting of prokaryotes into bacteria and archaea
Eukaryotes Korarchaeotes Euryarchaeotes Crenarchaeotes Nanoarchaeotes Proteobacteria Chlamydias Spirochetes Cyanobacteria Domain Bacteria Domain Archaea UNIVERSAL ANCESTOR Gram-positive
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Clades of Domain Bacteria
Fig (27.13 in 7th ed.) Proteobacteria diverse & includes gram-negatives Subgroups: α, β, γ, δ, ε Chlamydias Spirochaetes Cyanobacteria Gram positive bacteria
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Proteobacteria Alpha subgroup Rhizobium
Nitrogen-fixing bacteria reside in nodules of legume plant roots Convert atmospheric N2 to usable inorganic form for making organics (i.e. amino acids)
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Proteobacteria Gamma subgroup Includes many Gram negative bacteria
E. coli common intestinal flora Enterobacter aerogenes Pathogenic; causes UTI Serratia Facultative anaerobe Characteristically red cultures
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Proteobacteria: Myxobacteria
Delta subgroup of Proteobacteria Slime-secreting decomposers Elaborate colonies Thrive collectively, yet have the capacity to live individually at some point in their life cycle Release myxospores from “fruiting” bodies
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Chlamydias parasites that live within animal cells
Chlamydia trachomatis causes blindness and nongonococcal urethritis by sexual transmission Chlamydias 2.5 m Chlamydia (arrows) inside an animal cell (colorized TEM)
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Spirochaetes Long spiral or helical heterotrophs
Flagellated cell wall Decomposers & pathogens Some are parasites, including Treponema pallidum, which causes syphilis, and Borrelia burgdorferi, which causes Lyme disease
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Cyanobacteria “blue-green algae” Photoautotrophic Typically colonial
Generate O2 as a significant primary producer in aquatic systems Typically colonial Filamentous Plant chloroplasts likely evolved from cyanobacteria by the process of endosymbiosis
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Oscillatoria (Cyanobacteria) 1
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Oscillatoria 2
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Anabaena (Cyanobacteria) 1
Vegetative cell Primary metabolic function (photosynthesis) Heterocyst Nitrogen fixation Akinete Dormant spore forming cell
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Anabaena 2
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Anaebena 3
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Nostoc (Cyanobacteria) 1
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Nostoc 2
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Gleocapsa (Cyanobacteria) 1
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Gleocapsa 2
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Gram positive bacteria
Gram stains – purple Thick cell wall Includes: Micrococcus Common soil bacterium M. luteus cultures have a yellow pigment Some Staphylococcus and Streptococcus, can be pathogenic Bacillus B. subtilis are relatively large rods; common “lab organism” Bacillus anthracis, the cause of anthrax Actinomycetes, which decompose soil Clostridium botulinum, the cause of botulism Mycoplasms, the smallest known cells Hundreds of mycoplasmas covering a human fibroblast cell (colorized SEM)
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Domain Archaea
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Archaea -- “Extremophiles”
Many are tolerant to extreme environments Extreme thermophiles High and low temperature Commonly acidophilic E.g. hot sulfer springs, deep sea vents Extreme halophiles High salt concentration Often contains carotenoids E.g. Salton Sea Methanogens Anaerobic environments Release methane E.g. animal guts
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