Prokaryote diversity Level 1 Biological Diversity Jim Provan Campbell: Chapter 27

Prokaryotes are (almost) everywhere Prokaryotes dominate the biosphere: Collective mass of prokaryotes outweighs eukaryotes tenfold More prokaryotes in the average human mouth than all the humans that ever lived Prokaryote diversity: About 5,000 species known Actual numbers believed to be 400,000 to 4 million

The three domains of life Domain Bacteria Domain Bacteria Domain Archaea Domain Archaea Domain Eukarya Domain Eukarya

Diversity of prokaryotic cell shapes

Prokaryote cell walls

Present in nearly all prokaryotes: Provides physical protection Prevents cells from bursting in hypotonic environment Reason prokaryotes were sometimes grouped with plants in early classification systems Cell wall contains peptidoglycan, rather than cellulose: Gram-negative bacteria generally more pathogenic than gram-positive bacteria: –Lipopolysaccharides can be toxic –Outer membrane less permeable to antibiotics Antibiotics inhibit cross-linking of peptidoglycan

Prokaryote organisation Prokaryotes have smaller, simpler genomes than eukaryotes: On average, about one-thousandth as much DNA Concentrated in twisted nucleoid region Single, circular chromosome Also have “accessory” DNA – plasmids General mechanism of DNA replication and protein translation is largely the same as in eukaryotes No organelles, but some have specialised membranes which carry out similar functions

Prokaryote organisation

Prokaryote reproduction Prokaryotes reproduce only asexually by binary fission: DNA synthesis is almost continuous No mitosis or meiosis Gene transfer is possible: Transformation – take up of genes from surroundings Conjugation – direct transfer of genes between cells Transduction – gene transfer by viruses Mutation is the major source of genetic variation “Growth” is actually increase in numbers, which effectively proceeds geometrically

Prokaryote metabolic diversity ModeEnergy sourceCarbon source Example PhotoautotrophLightCO 2 Cyanobacteria, plants, protists ChemoautotrophInorganic compoundsCO 2 Some prokaryotes (Sulfolobus) PhotoheterotrophLightOrganic compoundsSome prokaryotes ChemoheterotrophOrganic compounds Organic compounds Prokaryotes, protists, fungi, animals, parasitic plants

A survey of prokaryote diversity DOMAIN EUKARYA  ChlamydiasSpirochetes Gram positive bacteria Cyanobacteria Proteobacteria DOMAIN BACTERIA EuryarchaeotaCrenarchaeota DOMAIN ARCHAEA

The three domains of life BacteriaxxUnbranchedOnef-MetxInhibitedxArchaeaxxx Some branched SeveralMet Not inhibited EukaryaxUnbranchedSeveralMet CHARACTERISTIC Nuclear envelope Organelles Peptidoglycan cell wall Membrane lipids RNA polymerase Initiator amino acid Introns Antibiotic response HistonesDOMAIN

Domain Archaea Inhabit most extreme environments: Methanogens - strict anaerobes which use H 2 to reduce CO 2 to methane (CH 4 ) Extreme halophiles - live in saline environments five to ten times saltier than sea water Extreme thermophiles - live in very hot environments such as sulphur springs of deep-sea hydrothermal vents

Domain Bacteria: Proteobacteria

Domain Bacteria: others

Ecological impact of prokaryotes Prokaryotes are crucial components of ecosystems: Decomposition of waste products Recycling of elements from inorganic sources (soil, air etc.) Many prokaryotes are symbiotic: Rhizobium – N 2 fixation Bioluminescence

Some prokaryotes are pathogenic Pathogenic prokaryotes cause half of all human disease Some pathogens are opportunistic: they cause illness when the host’s defences are weakened Mostly produce toxins: Exotoxins secreted by prokaryotes e.g. in food or water Endotoxins are components of bacterial membranes

Humans use prokaryotes Used as model systems to study genetics e.g. Escherichia coli Used in bioremediation: Sewage treatment Decomposition of oil spills by soil bacteria Metabolic “factories”: Organic solvents Antibiotic production Food industry