MC5-6: Bacterial metabolism and phototrophy Flashcards
When did bacteria evolve?
Approx. 3.5 billion years ago
How many species of animals, plants, and bacteria are there on Earth?
Animals: 10–30 x106
Plants: (estimated) 300,000
Bacteria: (estimated) 107 – 109
How many cells are there on Earth at any one time?
4–6 x1030 cells
Where are the majority of bacteria and archaea found?
Open ocean: 1.2 x1029
Soil: 2.6 x1029
Oceanic sediment: 3.5 x1030
Terrestrial sediment: 0.25–2.5 x1030
Human guts: approx. 3.9 x1023
Define ‘metabolism’
The set of chemical reactions that occur in living organisms in order to mainain life. Metabolic processes allow organisms to grow, reproduce, maintain structures, and respond to their environments
Define ‘catabolism’
Breaking down organic matter, e.g. to harvest energy in cellular respiration
Define ‘anabolism’
The use of energy to contruct components of cells such as proteins and nucleic acids
What are the three basic requirements for life?
- Energy source
- Carbon source
- Electron source
What are the two different possibilities for obtaining energy, and what are the processes that lead to energy obtention?
-
Phototrophy – ‘eating’ light energy
- Photosynthesis – converting CO2 to sugars using sunlight energy
-
Chemotrophy – ‘eating’ chemical bond energy
- Respiration – transforming energy from nutrients into chemical energy with O2 usually as the terminal electron acceptor
- Fermentation – process of energy production in cell under anaerobic conditions
What is the so-called ‘energy currency’ of bacteria, and what are the two methods by which this is generated?
ATP
Substrate-level phosphorylation and oxidative phosphorylation
What are the carbon sources of:
- autotrophs
- hterotrophs?
- Autotrophs = CO2
- Heterotrophs = organic compounds
Where do:
- photoautotrophs
- photoheterotrophs
- chemoheterotrophs
- chemoautotrophs
get their energy and carbon from?
-
Photoautotroph
Energy = light
Carbon = CO2 -
Photoheterotroph
Energy = light
Carbon = organic compounds -
Chemoheterotroph
Usually, a single organic compound acts as a source for both energy and carbon -
Chemoautotroph
Energy = oxidation of inorganic chemical compounds
Carbon = CO2
What are the four nutritional categories of life?
- Photoautotroph
- Photoheterotroph
- Chemoautotroph
- Chemoheterotroph
Why can O2 be very harmful to organisms without protective mechanisms?
It is a harsh oxidising agent
What is the name for organisms that can grow in oxygen?
Aerobes
How do aerobes utilise oxygen?
They use aerobic respiration as their principle energy generation by using O2 as their terminal electron acceptor
Why can anaerobes not live in oxygenated environments?
They never developed protective mechanisms against oxygen
Give two examples of environments in which anaerobes live.
- Animal intestinal tract
- Lake/ocean sediments
What is different about anoxygenic photosynthesis?
- Carried out in oxygen-free environments
- Electron donor is water
- No oxygen is produced
What are the types of aerobic and anaerobic metabolism?
Aerobic
- Aerobic respiration
- Oxygenic photosynthesis
- Anoxygenic photosynthesis
Anaerobic
- Fermentation
- Anaerobic respiration
- Anoxygenic photosynthesis
How is ATP generated in bacteria?
Phototrophy
- Pigments absorb energy from the sun
- An electron with a higher energy level is then released from within the pigment
- This electron is passed through an electron transport chain, with the generation of energy by formation of ATP
What is the carbon source of:
- autotrophs
- heterotrophs
- mixotrophs?
- Autotrophs: CO2
- Heterotrophs: organic compounds
- Mixotrophs: both
What are the two types of phototrophy and how do they differ?
-
Anyoxygenic
- Used bacteriochlorophyll
- Has 1 reaction centre
-
Oxygenic
- Uses chlorophyll
- Has 2 reaction centres
What are the five major groups of prokaryotes that use anoxygenic photosynthesis, and which group used oxygenic photosynthesis?
Anoxygenic
- Purple sulphur bacteriochlorophyll b
- Purple non-sulphur bChl a b
- Green non-sulphur bChl a b
- Green sulphur bChl c d e f
- Heliobacteria bChl g
Oxygenic
- Cyanobacteria chla
What do purple sulphur bacteria use as an electron donor? Give examples of the bacteria.
- H2S
- Thiopedia roseopersicinia
- Ameobacter purpureus
What do purple non-sulphur bacteria use as an electron donor? Give examples of typical genera.
- Hydrogen
- Rhodospirillum
- Rhodopseudomonas
- Rhodobacter
What do green sulphur bacteria use as electron donors? Give examples of species.
- H2S / S / S2O32– (which invariably becomes H2SO4)
- Chlorobium species
What do green non-sulphur bacteria use as electron donors? Give an example of a species.
- Hydrogen
- Chloroflexus
What do heliobacter use as an electron donor?
H2S
What are the only oxygenic phototrophic prokaryotes?
Cyanobacteria
What do cyanobacteria use as an electron donor? Name the two main genera
- Water
- Synechococcus
- Prochlorococcus
What are the seven reasons for studying microbial metabolism?
- Medical microbiology
- Microbiome
- Diagnostic microbiology
- Pharmaceutical microbiology
- Biotechnology
- Many foods/drugs of plant origin owe their taste/smell/active constituents to microbial metabolism
- Environmental microbiology
How is energy accessed by chemotrophs?
By harnessing and linking oxidation/reduction pairs
What does OILRIG mean?
- *O**xidation
- *I**s
- *L**oss (of electrons)
- *R**eduction
- *I**s
- *G**ain (of electrons)
On which side of a redox pair is the oxidised form always written?
Left
What is the redox potential and how is it measured?
Redox potential = E’0 = the capacity of a pair to donate or accept electrons
Measured electrically by reference to a standard
Finish the sentence:
Half-reactions with positive redox tend to ______ electrons; half-reactions with negative redox tend to ______ electrons.
Half-reactions with positive redox tend to donate electrons; half-reactions with negative redox tend to accept electrons.
What are the two mechanisms chemoheterotrophs have for energy conservation?
What drives the synthesis of ATP in both?
Respiration and fermentation
Driven by energy released in redox reactions
Describe the oxidase test
- Filter paper impregnanted with redox dye (TMPD) which artificially donates an electron to the cytochrome
- The cytochrome system is usually only present in aerobic organisms that are capable of using electron as the terminal electron acceptor
- Turns purple if the dye is oxidised by oxygen released from metabolic reaction
Where do Deinococcus species of bacteria grow?
On sugars, amino acids, organic acids, and mixtures of these
What is the best studied of the Deinococcus species?
D. radiodurans
Give two examples of Spirochetes and the diseases they cause.
- Treponema – causes syphilis
- Borrelia – causes Lyme disease
What is the relevance of Spricohetes having a helical structure?
It allows them to move in a corkscrew motion through viscous media such as mucus
What do Planctomyces lack in their cell walls?
Peptidoglycan
What type of prokaryote produce methane?
Methanogenic archaea in anoxic environments
What are methanotrophs and methylotrophs?
- Methanotrophs produce methane
- Methylotrophs grow on one-carbon compounds including methane
What are diazotrophs? Give an example.
Bacteria that reduce nitrogen (N2)
e.g. Azotobacter
Are Azotobacter Gram positive or Gram negative?
Gram negative
How do Azotobacter contribute to biogeochemical cycling?
They grow on a range of carbohydrates, alcohols, and organic acids and fix N2 non-symbiotically
What are Rhizobia?
N2-fixing symbiont of legumes
How are chemoautotrophs specialist?
They can find unique niche zones where chemoheterotrophs cannot live
What are the three sources of inorganic electron donors?
-
Geological
- e.g. volcanic activity producing H2S
-
Biological
- Producing H2S, H2, NH3
-
Anthropogenic (human influence)
- e.g. agriculture, mining, burning fossil fuels, input of industrial wastes
Give examples of the chemoautotrophs that are at the heart of most nutrient cycles
Aquifex, nitrosifyers such as Nitrosococcus, nitrifyers such as Nitrobacter, Thiobacillus, Thiomicrospira, Thiothrix
Describe the metabolism of nitrosifiers
They oxidise ammonia to to nitrites
Describe the metabolism of nitrifyers
They oxidise nitrites to nitrates
Describe the metabolism of sulphur-oxidising bacteria
They oxidise sulphur, using oxygen as a terminal electron acceptor
Describe the metabolism of iron-oxidisers
They oxidise iron:
- Ferric iron to insoluble ferric hydroxide which precipitates in water
- Ferrous iron to ferric state at neutral pH
