Ch 27 Prokaryotes Bacteria and Archaea Prokaryotes are
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
Prokaryotes • Single cell – 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)
Bacilli • Rod shaped – Example: E. coli • Usually solitary • Sometimes chains – streptobacilli
Cocci • Spherical – Clumps or clusters (like grapes) • E. g. Staphylococcus aureus – Streptococci – chains of spheres – Diplococci – pairs of spheres • E. g. Neisseria gonnorheae
Streptococcus 1
Streptococcus 2
Diplococcus 1
Diplococcus 2
Spiral prokaryotes • Spirilla – spiral shaped – With external flagella – Variable lengths • Spirochaetes – Internal flagella – Corkscrew-like • Boring action • E. g. Treponema pallidum (Syphilis)
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
• Can use the Gram stain to classify bacteria by cell wall composition – Counter stains to differentiate between cell wall characteristics Gram-positive bacteria Gram-negative bacteria 10 m – 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 • Thick layer of peptidoglycans • Retains crystal violet – Doesn’t wash out – Masks red safranin • Stains dark purple or blue-black
Gram negative bacteria • Thin sandwiched layer of peptidoglycans • Rinses away crystal violet • Stains pink or red (b) Gram-negative bacteria: crystal violet is easily rinsed away, revealing red dye. Carbohydrate portion of lipopolysaccharide Outer membrane Cell wall Peptidoglycan layer Plasma membrane
• Extra capsule covers many prokaryotes Bacterial cell wall – polysaccharide or protein layer Bacterial capsule Tonsil cell • 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 200 nm Fimbriae 1 m
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 CO 2 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
The Role of Oxygen in Metabolism • Prokaryotic metabolism varies with respect to O 2 – Obligate aerobes – require O 2 for cellular respiration – Obligate anaerobes – are poisoned by O 2 and use fermentation or anaerobic respiration – Facultative anaerobes – can survive with or without O 2
Nitrogen Metabolism • Nitrogen is essential for the production of amino acids and nucleic acids – nitrogen fixation – some prokaryotes convert atmospheric nitrogen (N 2) to ammonia (NH 3) – 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
Molecular systematics led to the splitting of prokaryotes into bacteria and archaea Eukaryotes Euryarchaeotes Crenarchaeotes UNIVERSAL ANCESTOR Nanoarchaeotes Domain Archaea Korarchaeotes Proteobacteria Spirochetes Fig 27. 15 Cyanobacteria Gram-positive Domain Bacteria Chlamydias
Clades of Domain Bacteria see Fig 27. 16 • Proteobacteria – diverse & includes gram-negatives – Subgroups: α, β, γ, δ, ε • • Chlamydias Spirochaetes Cyanobacteria Gram positive bacteria
Proteobacteria • Alpha subgroup • E. g. Rhizobium – Nitrogen-fixing bacteria reside in nodules of legume plant roots – Convert atmospheric N 2 to usable inorganic form for making organics (i. e. amino acids)
Proteobacteria Beta subgroup • diverse soil and aquatic species; and some pathogens – Neisseri gonorrhoeae & N. meningitidis • Aerobic, gram neg, and diplococci – Bordetella pertussis • causes pertussis (whooping cough)
Proteobacteria Gamma subgroup • Includes many Gram negative bacteria – E. coli • common intestinal flora – Enterobacter aerogenes • Pathogenic; causes UTI – Serratia • Facultative anaerobe • Characteristically red cultures
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
Clades of Domain Bacteria see Fig 27. 16 • Proteobacteria – diverse & includes gram-negatives – Subgroups: α, β, γ, δ, ε • • Chlamydias Spirochaetes Cyanobacteria Gram positive bacteria
Chlamydias 2. 5 m • parasites that live within animal cells • Chlamydia trachomatis causes blindness and nongonococcal urethritis by sexual transmission Chlamydia (arrows) inside an animal cell (colorized TEM)
Clades of Domain Bacteria see Fig 27. 16 • Proteobacteria – diverse & includes gram-negatives – Subgroups: α, β, γ, δ, ε • • Chlamydias Spirochaetes Cyanobacteria Gram positive bacteria
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
Clades of Domain Bacteria see Fig 27. 16 • Proteobacteria – diverse & includes gram-negatives – Subgroups: α, β, γ, δ, ε • • Chlamydias Spirochaetes Cyanobacteria Gram positive bacteria
Cyanobacteria • “blue-green algae” • Photoautotrophic – Generate O 2 as a significant primary producer in aquatic systems • Typically colonial – Filamentous • Plant chloroplasts likely evolved from cyanobacteria by the process of endosymbiosis
Anabaena (Cyanobacteria) 1 • Vegetative cell – Primary metabolic function (photosynthesis) • Heterocyst – Nitrogen fixation • Akinete – Dormant spore forming cell (no movement)
Anabaena 2
Anaebena 3
Oscillatoria (Cyanobacteria) 1
Oscillatoria 2
Nostoc (Cyanobacteria) 1
Nostoc 2
Gleocapsa (Cyanobacteria) 1
Gleocapsa 2
Clades of Domain Bacteria see Fig 27. 16 • Proteobacteria – diverse & includes gram-negatives – Subgroups: α, β, γ, δ, ε • • Chlamydias Spirochaetes Cyanobacteria Gram positive bacteria
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)
Domain Archaea
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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