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

Diversity of prokaryotic cell Diversity of prokaryotic cell shapesshapes

Prokaryote cell wallsProkaryote cell walls

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 organisationProkaryote organisation

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

MA

IN E

UK

AR

YA

Ch

lam

yd

ias

Sp

iroch

ete

s

Gra

m p

osit

ive

bacte

ria

Cyan

ob

acte

ria

Proteobacteria

DOMAIN BACTERIA

Eu

ryarc

haeota

Cre

narc

haeota

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

Domain Bacteria: ProteobacteriaDomain Bacteria: Proteobacteria

Domain Bacteria: othersDomain Bacteria: others

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