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What are the principal differences between Archaea and Bacteria?
- rRNA nucleotide sequences– Cell wall and membrane lipids differ
- • A key evolutionary (and ecological) feature?
- Bacteria: – Are scarce in extreme environments – Can form endospores– Are associated with disease– Are more diverse in forms of energy acquisition (some can photosynthesize)
- Bacterial cell walls always contain peptidoglycan, but in differing amounts
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What is the significance of the Gram stain response?
- • Common diagnostic tool
- • Gram +ves (A monophyletic group)– very resistant to osmotic stress– can form endospores– usually chemoheterotrophs– non-motile and without appendages
- • Gram -ves (>9 different groups) – utilise periplasmic space for • Nutrient acquisition• Nutrient processing• Detoxifying environment
- • G+ves and G-ves often found together in microbial communities in organisms, soils, water bodies….
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Some Gram+ bacteria can form highly resistant dormant structures
- • Endospores: Gram positive only
- – E.g. Clostridium andBacillus spp. such as botulism and anthrax
- • Akinetes: Cyanobacteria
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Archaea
- • Cell walls: No peptidoglycan, but may or may not retain G stain depending on wall thickness
- • Membrane lipids: distinctive from both Bacteria and Eukarya in that lipid ‘tails’ are branched, and sometimes linked
- • Transcriptional machinery more similar to eukaryotes (TATA binding, etc)
- • 4 major functional groups:– Methanogens– Archaeal sulfate reducers– Extreme halophiles– Extreme thermophiles
- But they are frequent in soils, freshwater and marine environments
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energy/nutritional groups of prokaryotes
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Chemoheterotrophs: Saprobes = “The Decomposers/Recyclers”
- Energy and carbon supplied from organic compounds
- • Saprobes exist on non-living matter (e.g. Actinomycetes (such as Streptomyces), Azotobacter, Clostridium)
- • Metabolic product of one bacterial species is often the substrate for another (examples ahead)
- • Antibiotic production common
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Anaerobic chemoheterotrophy: Fermentation
- Respiration: Glucose + O2-> Energy + H2O + CO2Many bacteria (and archaea) evolved in, and thrive in, low oxygen environments
- Fermentation: When O2is low, chemical energy isoften released by metabolising pyruvate to: -Lactate by bacteria and archaea - Ethanol by fungi and plants
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Bacterial roles in food production
- – Lactobacteria (lactose –> lactic acid fermenters)• Milk products: Yogurt, Cheddar cheese, Mozzarella, Cottage cheese, cheese curds, Buttermilk……• Beers: Belgian ‘lambic style’ and Wheat beers• Bread: Sourdough• Pickled vegetables–
- Malo-lactic fermenters• Some Wines: Alsace and N American whites. Benefit from Malic to Lactic conversion that reduces acidity
- – Acetic acid fermenters (e.g. Acetobacter) Vinegar
- – Propionibacterium: E.g ‘eyes’ in ‘Swiss’ cheese
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Chemoheterotrophic symbionts: e.g. Rumen bacteria and archaea
- • Rumen: A specialised stomach containing prokaryotic cultures
- • An anaerobic culturing hotspot for prokaryotes
- • Eat twice –regurgitate fermented cud
- • Plant leaf and shoot material often dominated by cellulose
- • Prokaryotes and fungi produce cellulases
- • Cellulose -> (by cellulase) Glucose -> (via Fermentation) Acetate and fatty acids
- > Absorption into bloodstream for aerobic respiration by host animal
- > (via Methanogenesis) CH4in some animals
- eg. Legumes and Alder
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Chemoheterotrophs: Pathogenic and parasitic bacteria
Some animal hosts: PneumoniaLeprosyTetanusCholeraListeriosisSyphilis…
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Photoautotrophs
- Cyanobacteria (“Blue green algae”):
- CO2+ 2H20 (CH2O) n+ H20 + O2
- Purple and Green Sulfur bacteria:
- CO2+ 2H2S (CH2O) n+ H20 + 2S
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Cyanobacteria
- Pigments - chlorophyll a, phycobilins(phycocyanin, phycoerythrin)
- Resting stages - Akinetes
- Ability to fix nitrogen – Heterocysts
- Critical roles in:evolution of lifeglobal C and N cycles
- Storage capacities for C (glycogen), P and N
- Many symbiotic forms
- Stromatolites
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Chemoautotrophs
- Energy by oxidising sources such as NH4, Fe2+, S, HS-, CH4, H2 while fixing CO2for carbon
- • Nitrifiers: NH4-> Nitrate
- • Iron oxidisers: Fe2+ -> Fe3+
- • Sulfur oxidisers: S -> SO2-
- • Methanotrophs: CH4-> CO2
- • Some methanogens: H2-> CH4
- • Globally important biogeochemical transformations
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Methanogens
- • Only in the Archaea
- • Strictly anaerobic metabolism
- • Some methanogens are autotrophs, some are chemoheterotrophs (acetate ->CH4)
- • Natural gas (methane is odourless)
- • Methane a very important greenhouse gas
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Photoheterotrophs
- A purple nonsulfur bacterium, Rhodospirillum rubrum. Grown in low light, this individual has developed many photosynthetic pigments.
- Extraordinary metabolic flexibility…..photo OR chemoheterotrophy (+/-O2)Occur in mud and water of lakes, ponds and seashores where there is abundant organic matter and little sulfur (e.g. sewage polluted lakes)
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