Microbial metabolic diversity Flashcards
what are heterotrophs?
- use organic compounds
what are autotrophs?
- forms organic compounds from simple inorganic substances like CO2
what are chemoheterotrophs?
- main source of energy = organic chemical substances
- main source of carbon = organic compounds
- animals and fungi
what are chemoautotrophs?
- main source of energy = chemical, oxidise inorganic compounds
- carbon source = CO2
- extremophiles, mainly archaea
what are photoheterotrophs?
- energy source = light
- carbon source = organic compounds
- purple and green non-sulphur bacteria
what are photoautotrophs?
- energy source = light
- use light energy to form organic compounds from CO2
- plants, algae, cyanobacteria
what are organotrophs?
- oxidise organic materials for electrons e.g. amino acids and carbohydrates
CH2O + O2 = CO2 + H2O
what are lithotrophs?
- oxidise inorganic materials for electrons, including hydrogen sulphide and reduced iron
ferrous iron = ferric iron + e-
nitrite = nitrate + e-
sulphur = sulphate + e-
2H2O = 4H+ + 4e- + O2
what are the 3 main metabolic groups?
- chemoorganotrophy
- use reduced organic molecules such as sugars and lipids - chemolithotrophy
- use reduced inorganic molecules such as geological compounds - phototrophy
- use light energy to reduce compounds, then use these as electron donors
what is catabolism and anabolism?
catabolism = how molecules are broken down and how their energy is extracted
anabolism = synthesis of molecules and storage of compounds
what are the electron acceptors of respiration and fermentation?
respiration = organic and inorganic molecules
fermentation = organic molecules
what are the electron donors of metabolism?
Phototrophy: use light energy to reduce compounds, then use these as electron donor
Chemolithotrophy: inorganic molecules
Chemoorganotrophy: organic molecules
what is the electron transfer system?
- transfer of compounds from low reduction potential to high reduction potential
- a series of membrane electron transporters where electrons move from one compound to another according to their reduction potential
- generates energy conserved in the form of a transmembrane PMF which is used for ATP synthesis by ATP synthase
when is a chemical reaction only possible?
- if Gibbs free energy is negative
- a PMF of 180mV exists across the cytoplasmic membrane, so redox potential change must exceed this value to join ETC and proton translocation
what sources of energy does metabolism produce?
- reducing power: NADH, NADPH, FADH2
- ATP
the energy generated during ETC generates a proton gradient that drives ATP synthesis
in chemoorganotrophhy, what organic compounds are used as a source of electrons?
- carbohydrates
- lipids
- peptides
- aromatic compounds
in chemoorganotrophy, what 2 key metabolites are produced?
- acetyl coenzyme A (acetyl CoA)
- pyruvate
what energetic currencies are formed in chemoorganotrophy?
- ATP
- NADH+, H+, FADH2 (reducing power)
example of glucose metabolism
what are the 3 major metabolic types of chemoorganotrophy, depending on the electron acceptor?
- aerobic respiration
- oxygen is electron acceptor - anaerobic respiration
- produces less energy due to lack of oxygen, so reduction potential stays low
- inorganic substrate is acceptor - fermentation
- organic substrate is acceptor, usually pyruvate
what are the 3 major metabolic types of chemoorganotrophy, depending on the electron acceptor?
- aerobic respiration
- oxygen is electron acceptor - anaerobic respiration
- produces less energy due to lack of oxygen, so reduction potential stays low
- inorganic substrate is acceptor - fermentation
- organic substrate is acceptor, usually pyruvate
what is oxygenic respiration?
very high energy output:
- 2ATP from glycolysis
- 2ATP from TCA cycle
- 10NADH and 2FADH2 from oxidation
- up to 38ATP overall
what is anoxygenic/anaerobic respiration?
- has a wide range of inorganic compounds that can be used as electron acceptors
- ETC occurs via cytochromes, quinones and iron-sulphur proteins
- bacteria use anaerobic respiration when O2 is not available
- different amounts of energy are generated depending on the redox potential of the electron acceptor
- important in a wide range of ecological niches
what is denitrification?
- process in which nitrates are converted into nitrogen
nitrate is reduced to nitrite. nitrite is reduced to nitric oxide. nitric oxide is reduced to nitrous oxide. nitrous oxide is reduced to nitrogen
uses reductase enzymes
what is methanogenesis?
- production of methane by microorganisms
- CO2 is electron acceptor
Acetate
- CH3-COO- + H+ -> CH4 + CO2
Methanol
- 4CH3OH -> 3CH4 + CO2 + 2H2O
Chemolithoautotrophs
- 4H2 + CO2 -> CH4 + 2H2O
what is fermentation?
- occurs under anaerobic conditions
- use of organic molecules as electron acceptors, without the use of a respiratory chain
- ATP is produced by substrate-level phosphorylation in the cytoplasm
- low energy yields, as cells grow more slowly than when they respire
what differentiates anaerobic respiration and fermentation?
anaerobic respiration:
- inorganic molecules (not O2) or organic molecules as electron acceptor
- uses membrane-bound respiratory chain
- ATP produced by oxidative phosphorylation via PMF
fermentation:
- organic molecules as electron acceptor
- no respiratory chain
- ATP produced by substrate-level phosphorylation in the cytoplasm
what are the major electron sources in chemolithotrophy?
- can extract electrons from many compounds to power metabolism
what are important properties of chemolithotrophs?
- use CO2 as a carbon source to produce organic molecules via Calvin cycle and reverse TCA cycle
- can use complex molecules like acetate
- require NADH to fix carbon, which requires consumption of H+ for reverse electron flow
what is hydrogenotrophy?
- uses H2 as electron donor
- hydrogenotrophs can use a wide range of acceptors
what are examples of electron acceptors in hydrogenotrophy?
O2: formation of water H2 + ½ O2 -> H2O
SO42-:
4H2 + SO42- + H+ -> HS- + 4H2O
CO2: methanogenesis 4H2 + CO2 -> CH4 + 2H2O
Compounds such as formiate or acetate can also be used as electron acceptor, yielding CO2 and CH4
chlorinated compounds (dehalorespiration): detoxification of compounds which contain high amount of chloride
what is iron oxidation?
reduced iron (Fe2+) can be oxidised to ferric iron (Fe3+) at low pH: 2Fe2+ + ½ O2 + 2H+ = 2Fe3+ H2O
ferric iron forms insoluble ferric hydroxide as pH gets lower:
o Fe3+ + 3H2O = Fe(OH)3 + 3H+
electron acceptors other than oxygen can be used e.g. nitrates can be reduced to nitries
what is nitrogen oxidation?
- ammonia (NH3) and nitrites (NO2-) can be used as electron donors to produce nitrates (NO3-)
- can occur in aerobic or anaerobic conditions depending on the organism
nitrification occurs in aerobic conditions
anammox occurs in anaerobic conditions
what is sulphur oxidation?
- sulphur derivatives can be used as electron donors to produce sulphuric acid
- Elemental sulphur: S0
- Hydrogen sulphide: H2S
- Thiosulphate: S2O32-
- Ferrous disulphide (pyrite): FeS2
how are acid-producing microbes used in biomining?
Acidothiobacillus ferrooxidans:
- oxidise sulphide of iron and copper
- the oxidation of Cu+ andd acid production dissolves the metal from the rocks
- improves metal extraction
what phototropic organisms undergo oxygenic photosynthesis?
- cyanobacteria and plants
- use photosystems I and II
what phototropic organisms undergo anoxygenic photosynthesis?
- bacteriorhodopsin
- photosystem BR - green sulphur bacteria
- PSI - purple bacteria
- PSII
what is bacteriorhodopsin (BR)?
- light-driven proton pump in archaea membranes
- contains retinal pigment that undergoes conformational change from trans to cis when excited by light
- shape change allows proton movement from the BR
- light replenishes the proteins with protons
- proton movement generates a gradient to produce ATP
where does oyxygenic photosynthesis occur in plants?
- in thylakoid membranes of chloroplasts, which stack to form grana
what are cyanobacteria?
- oxygenic photosynthesisers which have no chloroplasts
- their photosynthetic apparatus is variable, mostly made of thylakoids
how do cyanobacteria undergo oxygenic photosynthesis? oxygenic Z pathway
- light is captured by Light Harvesting Complexes (LHC)
- LHCs contain pigments which can use different wavelengths of light
- 2 photosystems are excited by light
- light provides energy to strip e- from H2O, forming H+
- electron flow is used to pump protons to outside of cell and reduce NADP+ to NADPH
- H+ gradient generates ATP
- ATP and NADPH are used to fix CO2 and make glucose
- 2H2O forms O2, 2NADPH and 3ATP
how many times must the oxygenic Z pathway run to form 1 molecule of glucose?
6
what is the process of anoxygenic photosynthesis in green sulphur bacteria?
- light captured by antenna complexes in organelles called chlorosomes
- photon energy is transferred to PSI, which donates an e- to ETC
- ETC pumps protons outside the cell to reduce NADP+ via ferrodoxin
- H+ gradient generates ATP
- PSI receives e- from inorganic sulphur derivatives (H2, H2S)
what is the process of anoxygenic photosynthesis in purple sulphur bacteria?
- light captured by antenna complexes in chromatophores
- photon energy transfers to PSII
- PSII donates an electron to cyclic ETC
- ETC pumps protons outside the cell
- H+ gradient generates ATP by cyclic photophosphorylation
- NADH isn’t produced as no transporter has reducing potential electronegative enough
- inorganic compounds H2, H2S are used as electron donors to produce NADPH
- reverse electron flow
