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MICR3310 > 3 - Microbes and the Carbon Cycle > Flashcards

3 - Microbes and the Carbon Cycle Flashcards

1
Q

Biogeochemical cycles

A
  • Movement and transformation of chemical elements and compounds between living organisms, the atmosphere, and the Earth’s crust
  • Catalysed by biological or chemical means (or both)
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2
Q

Nutrient cycles

A
  • E.g. Carbon, Nitrogen, Oxygen, Water
  • Are tightly coupled (transformations in one cycle may impact other cycles)
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3
Q

Two important types of metabolism

A

Assimilative and dissimilative

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4
Q

Assimilative

A

Compound usually incorporated into cell material (it is a nutrient)

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5
Q

Dissimilative

A

Compound used as an electron acceptor, generates “waste”

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6
Q

Example of coupled cycle

A

C and N which make up the bulk of living organisms

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7
Q

Rate of primary production (CO2 fixation)

A
  • Controlled by the availability of nitrogen
  • N usually low –> process is decreased, if high then increased
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8
Q

Carbon cycle

A
  • Microbes require carbon, energy and electrons (autotrophs get carbon from co2, heterotrophs get carbon from organic matter)
  • 3 important chemical forms of carbon and 3 important components of the carbon cycle
  • All other nutrient cycles are linked in some way to carbon cycle
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9
Q

3 important chemical forms of carbon

A
  • CO2 (highly mobile, rapidly exchanged)
  • Methane (important in climate change)
  • Organic matter (important sink, also primary production)
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10
Q

3 important components of the carbon cycle

A
  • Sources
  • Sinks
  • Reservoirs
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11
Q

Sources

A
  • Generate/release C
  • E.g. Heterotrophic microbes releasing CO2 during respiration
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12
Q

Sinks

A
  • Absorb, accumulate and store C for an indefinite period
  • E.g. Biomass (plants) that take up CO2 from atmosphere, dead plant material (humus), oceans
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13
Q

Flux

A

Movement between sources and sinks

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14
Q

Respiration equation

A

C6H12O6 + 6O2 –cellular respiration–> 6CO2 + 6H2O + ATP

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15
Q

Reservoirs

A

Store C for long time periods

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16
Q

Examples of reservoirs

A
  • Rocks and sediments make up majority
  • Also found in land plants (mainly dead)
  • Soil carbon
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17
Q

Major reservoirs that carbon cycles through

A
  • Rocks
  • Oceans
  • Methane hydrates
  • Fossil fuels
  • Biosphere
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18
Q

Biological pump

A

Process by which inorganic carbon is removed from the atmosphere and sequestered in the ocean

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19
Q

Biological pump process

A
  • CO2 converted to organic matter (photosynthesis & primary production, microbial and non microbial)
  • Some organic matter sinks (into deep sediments)
  • some is recycled back into atmosphere (flux)
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20
Q

Forms carbon is present in

A
  • Most oxidised form is CO2, CO
  • Most reduced form is methane and complex organ matter
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21
Q

Primary production

A

The synthesis of organic compounds from atmospheric or aqueous carbon dioxide

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22
Q

Carbon fixation

A
  • Starts with conversion of CO2 into organic matter or methane
  • CO2 is the most rapid means of transfer of carbon (removed from the atmosphere via photosynthesis and returned via respiration)
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23
Q

3 ways CO2 is converted into organic matter

A
  • Oxygenic photosynthesis
  • Chemolithoautotrophy
  • Anoxygenic photosynthesis
24
Q

Oxygenic photosynthesis

A
  • By photoplankton
  • CO2 +H2O –> CH2O (organic matter) + O2
25
Q

Chemolithoautotrophy

A

In both oxic and anoxic environments

26
Q

How much of Earths’ oxygen is created by phytoplankton through photosynthesis

A

50-85%

27
Q

How is CO2 reduced to methane

A
  • Methanogenesis (biological formation of methane)
  • Methane is end product (waste)
28
Q

Methanogenesis

A
  • A major process in anoxic environments (freshwater sediments, intestines of animals)
  • Performed by methanogens (archaea) - strict anaerobes
  • Methane formed from CO2 + H2 or H2 + acetate or organic matter decomposition
29
Q

Major mechanism of methane formation

A
  • Reduction of CO2 (TEA) using H2 as an electron donor
  • Most methanogens use this process
30
Q

Minor mechanism of methane formation

A
  • CH4 from organic matter
  • Much more complicated and requires help from syntrophs
31
Q

Methanogenesis equation

A

CO2 + 4H2 → CH4 + 2H20

32
Q

Syntrophy

A
  • Cooperation by two or more different microbes to degrade a single substance that neither can degrade alone
  • Important for aromatic and aliphatic hydrocarbons
  • Also important for fatty acids and alcohols as methanogens cannot
    directly catabolise these
33
Q

What do primary fermenters produce

A
  • H2, CO2, acetate, fatty acids and alcohols
  • Methanogens can use acetate and H2, but not fatty acids and alcohols
  • Rely on syntroph partner
34
Q

Partner syntrophs

A
  • Secondary fermenters
  • They metabolise products of primary fermenters and produce acetate, H2, CO2
  • In doing so, syntrophs supply methanogens with molecules that they can use
  • Syntrophs cannot do this alone in pure culture
35
Q

Why cant syntrophic metabolise products of primary fermenters in a pure culture

A
  • As they rely on methanogens to consume the H2 produced
  • H2 consumption makes reactions energetically favourable
  • Known as inter-species hydrogen transfer
36
Q

Example syntrophy

A
  • Butyrate fermentation has positive energy (+ 48.2 kJ)
  • Requires energy for reaction to occur
  • Will not happen in pure culture (single organism)
  • When H2 is consumed by methanotrophs and concentration reduced to extremely low levels,
    the reaction is pulled towards the reaction products
  • Dramatically alters energetics of the reaction and the reaction becomes exergonic G = -18 kJ
37
Q

Another example of syntrophy

A
  • Ethanol fermentation to acetate coupled with methanogenesis
  • Ethanol fermentation (+19.4) is energetically unfavourable so organism will not grow alone
  • Methanogenesis (-130.7), energetics Ok. produces H2 that ethanol fermenter consumes
  • Coupled reaction has a negative ΔG0’
38
Q

What is CO2 converted to

A

Organic molecules or methane

39
Q

Cycling of organic matter

A
  • Fixed carbon enters a pool of organic matter (can be oxidised back into CO2 via respiration or fermentation)
  • Microbial decomposition of organic matter contributes most of the CO2 to the atmosphere
40
Q

What is bioavailability and degradation of organic matter influenced by

A
  1. Type of organic matter
  2. Oxidation-reduction potential
  3. Availability of competing nutrients
  4. Abiotic conditions (pH, temp, o2)
  5. The microbial community present (metabolic/functional diversity)
41
Q

Example of complex organic substances

A

Lignin

42
Q

Lignin

A
  • Second most abundant organic molecule on earth after cellulose
  • Family of complex polymers
  • Exceptionally stable plant structural material
  • Linked by carbon-carbon and carbon-oxygen (ether) bonds
43
Q

Lignin decomposition

A
  • Fungi are excellent degraders
  • Bacteria have role but are slower
44
Q

Aerobic lignin decomposition

A
  • Mostly Actinomycetes (filamentous soil microbes)
  • Secrete hydrolytic enzymes e.g. lignin peroxidase, laccase
  • Degrade lignin by oxidative depolymerisation
  • Process requires oxygen
45
Q

Anaerobic lignin degradation

A
  • Very few microbes capable of this
  • Occurs very slowly
  • This is why lignified materials accumulate in anoxic environments
46
Q

Methane produced in sediments

A

Can be oxidised aerobically or anaerobically to CO2

47
Q

Aerobic oxidation of methane produced in sediments

A

By methanotrophic proteobacteria after diffusing to oxic areas

48
Q

Anaerobic oxidation of methane produced in sediments

A

By anaerobic methane oxidation or reverse methanogenesis

49
Q

Human impacts on carbon cycle

A
  • Current era called anthropocene
  • Greatest impacts from burning fossil fuels, deforestation and land use changes leading to increase atmospheric CO2
50
Q

Climate change and global warming

A
  • Atmospheric CO2 levels have increased by ~40% since the industrial revolution
  • CO2 is <0.5% of atmosphere but very effective at trapping infrared radiation emitted by earth
  • Oceans have absorbed substantial CO, slowing the effect
51
Q

Ocean acidification

A
  • Dissolution of CO2 in seawater produces carbonic acid (H2CO3)
  • Spontaneously dissociates into weak acids bicarbonate and carbonate
  • Extra H ions leads to ocean acidification
52
Q

Issue with excess H ions

A
  • Pushes equation towards bicarbonate which reduces available carbonate ions
  • Carbonate ions are important for combining with calcium carbonate
53
Q

Why is calcium carbonate important

A
  • For shells and skeletons of marine animals
  • Coccolithophores (primary producers)
  • Corals
  • Shellfish
54
Q

Methane hydrates

A
  • Methane present in atmosphere at lower levels than Co2 but 20 times more effective at trapping heat
  • Slow release of CH4 from sea floor hydrates feeds anaerobic methane-oxidising archaea and animal communities containing aerobic, methane-oxidising
    symbionts
55
Q

Human impact on methane hydrates

A
  • Vast quantities of CH4 are trapped underground beneath permafrost or in marine sediments
  • Mostly derived from microbial activity (convert organic matter to methane)
  • Highly dynamic, release and absorb methane in response to changed conditions
56
Q

Fate of methane

A

Could be oxidised to CO2 before reaching atmosphere

MICR3310 (28 decks)

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