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Prokaryote diversityProkaryote diversity
Level 1 Biological DiversityLevel 1 Biological Diversity
Jim ProvanJim Provan
Campbell: Chapter 27Campbell: Chapter 27
Prokaryotes are (almost) Prokaryotes are (almost) everywhereeverywhere
Prokaryotes dominate Prokaryotes dominate the biosphere:the biosphere:
Collective mass of Collective mass of prokaryotes outweighs prokaryotes outweighs eukaryotes tenfoldeukaryotes tenfoldMore prokaryotes in the More prokaryotes in the average human mouth average human mouth than all the humans that than all the humans that ever livedever lived
Prokaryote diversity:Prokaryote diversity:About 5,000 species About 5,000 species knownknownActual numbers believed Actual numbers believed to be 400,000 to 4 millionto be 400,000 to 4 million
The three domains of lifeThe three domains of life
DomainBacteriaDomainBacteria
DomainArchaeaDomainArchaea
DomainEukaryaDomainEukarya
Prokaryote cell wallsProkaryote cell walls
Present in nearly all prokaryotes:Present in nearly all prokaryotes:Provides physical protectionProvides physical protection
Prevents cells from bursting in hypotonic environmentPrevents cells from bursting in hypotonic environment
Reason prokaryotes were sometimes grouped with Reason prokaryotes were sometimes grouped with plants in early classification systemsplants in early classification systems
Cell wall contains Cell wall contains peptidoglycanpeptidoglycan, rather than , rather than cellulose:cellulose:
Gram-negative bacteria generally more pathogenic than Gram-negative bacteria generally more pathogenic than gram-positive bacteria:gram-positive bacteria:
– Lipopolysaccharides can be toxicLipopolysaccharides can be toxic– Outer membrane less permeable to antibioticsOuter membrane less permeable to antibiotics
Antibiotics inhibit cross-linking of peptidoglycanAntibiotics inhibit cross-linking of peptidoglycan
Prokaryote organisationProkaryote organisation
Prokaryotes have smaller, simpler genomes Prokaryotes have smaller, simpler genomes than eukaryotes:than eukaryotes:
On average, about one-thousandth as much DNAOn average, about one-thousandth as much DNA
Concentrated in twisted Concentrated in twisted nucleoid regionnucleoid region
Single, circular chromosomeSingle, circular chromosome
Also have “accessory” DNA – Also have “accessory” DNA – plasmidsplasmids
General mechanism of DNA replication and General mechanism of DNA replication and protein translation is largely the same as in protein translation is largely the same as in eukaryoteseukaryotes
No organelles, but some have specialised No organelles, but some have specialised membranes which carry out similar functionsmembranes which carry out similar functions
Prokaryote reproductionProkaryote reproduction
Prokaryotes reproduce only asexually by binary Prokaryotes reproduce only asexually by binary fission:fission:
DNA synthesis is almost continuousDNA synthesis is almost continuous
No mitosis or meiosisNo mitosis or meiosis
Gene transfer is possible:Gene transfer is possible:TransformationTransformation – take up of genes from surroundings – take up of genes from surroundings
ConjugationConjugation – direct transfer of genes between cells – direct transfer of genes between cells
TransductionTransduction – gene transfer by viruses – gene transfer by viruses
Mutation is the major source of genetic variationMutation is the major source of genetic variation
““Growth” is actually increase in numbers, which Growth” is actually increase in numbers, which effectively proceeds geometricallyeffectively proceeds geometrically
Prokaryote metabolic diversityProkaryote metabolic diversity
Mode Energy source Carbon source Example
Photoautotroph Light CO2 Cyanobacteria, plants, protists
Chemoautotroph Inorganic compounds CO2 Some prokaryotes (Sulfolobus)
Photoheterotroph Light Organic compounds Some prokaryotes
Chemoheterotroph Organic compounds Organic compoundsProkaryotes, protists, fungi,animals, parasitic plants
A survey of prokaryote diversityA survey of prokaryote diversity
DO
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Proteobacteria
DOMAIN BACTERIA
Eu
ryarc
haeota
Cre
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DOMAINARCHAEA
The three domains of lifeThe three domains of life
BacteriaBacteria
xx
xx
UnbranchedUnbranched
OneOne
f-Metf-Met
xx
InhibitedInhibited
xx
ArchaeaArchaea
xx
xx
xx
Some branchedSome branched
SeveralSeveral
MetMet
Not inhibitedNot inhibited
EukaryaEukarya
xx
UnbranchedUnbranched
SeveralSeveral
MetMet
Not inhibitedNot inhibited
CHARACTERISTICCHARACTERISTIC
Nuclear envelopeNuclear envelope
OrganellesOrganelles
Peptidoglycan cell wallPeptidoglycan cell wall
Membrane lipidsMembrane lipids
RNA polymeraseRNA polymerase
Initiator amino acidInitiator amino acid
IntronsIntrons
Antibiotic responseAntibiotic response
HistonesHistones
DOMAINDOMAIN
Domain ArchaeaDomain Archaea
Inhabit most extreme Inhabit most extreme environments:environments:
MethanogensMethanogens - strict - strict anaerobes which use Hanaerobes which use H22 to to reduce COreduce CO22 to methane to methane (CH(CH44))Extreme halophilesExtreme halophiles - live in - live in saline environments five to saline environments five to ten times saltier than sea ten times saltier than sea waterwaterExtreme thermophilesExtreme thermophiles - live - live in very hot environments in very hot environments such as sulphur springs of such as sulphur springs of deep-sea hydrothermal deep-sea hydrothermal ventsvents
Ecological impact of prokaryotesEcological impact of prokaryotes
Prokaryotes are Prokaryotes are crucial components of crucial components of ecosystems:ecosystems:
Decomposition of Decomposition of waste productswaste productsRecycling of elements Recycling of elements from inorganic sources from inorganic sources (soil, air etc.)(soil, air etc.)
Many prokaryotes are Many prokaryotes are symbiotic:symbiotic:
Rhizobium Rhizobium – N– N22 fixation fixationBioluminescenceBioluminescence
Some prokaryotes are Some prokaryotes are pathogenicpathogenic
Pathogenic prokaryotes Pathogenic prokaryotes cause half of all human cause half of all human diseasediseaseSome pathogens are Some pathogens are opportunisticopportunistic: they : they cause illness when the cause illness when the host’s defences are host’s defences are weakenedweakenedMostly produce toxins:Mostly produce toxins:
ExotoxinsExotoxins secreted by secreted by prokaryotes e.g. in food or prokaryotes e.g. in food or waterwaterEndotoxinsEndotoxins are are components of bacterial components of bacterial membranesmembranes
Humans use prokaryotesHumans use prokaryotes
Used as model systems Used as model systems to study genetics e.g. to study genetics e.g. Escherichia coliEscherichia coli
Used in Used in bioremediationbioremediation::Sewage treatmentSewage treatment
Decomposition of oil Decomposition of oil spills by soil bacteriaspills by soil bacteria
Metabolic “factories”:Metabolic “factories”:Organic solventsOrganic solvents
Antibiotic productionAntibiotic production
Food industryFood industry