Ch 27: Prokaryotes - Bacteria and Archaea

Great Salt Lake – pink color from living prokaryotes; survive in 32% salt

• 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

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

• 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-positivebacteria

10 m

Gram-negativebacteria

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 OutermembranePeptido-glycanlayer

Plasma membrane

Cellwall

Carbohydrate portionof lipopolysaccharide

(b) Gram-negative bacteria: crystal violet is easily rinsed away, revealing red dye.

• 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

Bacterialcell wall

Bacterialcapsule

Tonsilcell

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 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

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

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

Photosyntheticcells

Heterocyst

20 m

Molecular systematics led to the splitting of prokaryotes into bacteria and archaea

Eukaryotes

Korarchaeotes

Euryarchaeotes

Crenarchaeotes

Nanoarchaeotes

Proteobacteria

Chlamydias

Spirochetes

Cyanobacteria

Dom

ain BacteriaD

omain ArchaeaUNIVERSAL

ANCESTOR

Gram-positive

Clades of Domain Bacteria

• Fig 27.18 (27.13 in 7th ed.)• Proteobacteria– diverse & includes gram-negatives– Subgroups: α, β, γ, δ, ε

• Chlamydias• Spirochaetes• Cyanobacteria• Gram positive bacteria

• 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)

Proteobacteria

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

Chlamydias

• parasites that live within animal cells

• Chlamydia trachomatis causes blindness and nongonococcal urethritis by sexual transmission

Chlamydias

2.5

m

Chlamydia (arrows) inside ananimal cell (colorized TEM)

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

Cyanobacteria• “blue-green algae”• Photoautotrophic

– Generate O2 as a significant primary producer in aquatic systems

• Typically colonial– Filamentous

• Plant chloroplasts likely evolved from cyanobacteria by the process of endosymbiosis

Oscillatoria (Cyanobacteria) 1

Oscillatoria 2

Anabaena (Cyanobacteria) 1

• Vegetative cell– Primary metabolic function

(photosynthesis)

• Heterocyst– Nitrogen fixation

• Akinete– Dormant spore forming cell

Anabaena 2

Anaebena 3

Nostoc (Cyanobacteria) 1

Nostoc 2

Gleocapsa (Cyanobacteria) 1

Gleocapsa 2

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