6 - Harnessing the Power of Microbes Flashcards
1
Q
Processes microbes are responsible for
A
- Primary Production
- Decomposition
- Fixing nitrogen
- Methane production
- Industrial processes
2
Q
Great Atlantic Sargassum belt
A
- On land it decomposes and emits toxic gases
- Decomposition processes are aerobic and anaerobic
- Consumes O2 via aerobic respiration
- Creates anoxic areas (O2 does not penetrate underneath)
- Anaerobic decomposition generates H2S gas and NH3
- Gases have human health impacts
3
Q
Industrial processes microbes are involved in
A
- Mining (assist in extracting metals from low grade ores)
- Bioremediation (degrade environmental contaminants)
- Wastewater treatment (render water safe)
4
Q
Microbial leaching
A
- Process of concentrating metals in low-grade ore using microbes (useful when concentrations of metal are low)
- Minerals that are most readily oxidised are most amenable to microbial leaching (e.g. iron)
- May also be used for uranium and gold bioleaching
5
Q
Process for copper leaching
A
- Low grade ore is dumped in a large pile
- Dilute sulfuric acid (pH 2; rich in Fe3+) percolated through the pile
- Resulting liquid is rich in dissolved metals of interest
- Liquid transported to precipitation plant
- Metal is precipitated and purified
- Liquid recycled and returned to top of pile
- Rinse and repeat
6
Q
Low grade ore
A
Rocks with low concentration of ore of interest
7
Q
Two reactions that involve microbes in microbial leaching
A
- Acidothiobacillus ferooxidans oxidises the sulfide in CuS to SO4
2-, releases Cu2+ - Spontaneous oxidation of sulfide in CuS by Fe3+ (Fe3+ is generated by the bacterial oxidation of Fe2+ by different bacteria)
8
Q
Composition of microbial community changing with
temperature in microbial leaching
A
- A. ferrooxidans: mesophile, outcompeted when >30°C
- Leptospirillum ferrooxidans: mildly thermophilic ~40°C
- Archaea (e.g. Sulfolobus) dominate at 60-80°C:
9
Q
Acid mine drainage
A
- Caused by same microbial processes as bioleaching, but where mining operations are not done correctly
- Exposed sulfur rich ore + water + o2 + microbes
- Results from oxidation of sulfide minerals (bacterial or spontaneous)
- Problem in abandoned mines
- Acidic water leaches into surrounding waterways
10
Q
Two important reactions in acid mine drainage
A
- initiator: development of acidic conditions (SO4
2- + H+) - propagation: FeS2 is oxidised; leads to more H2
SO4
11
Q
Bioremediation
A
- Use of microbes to clean up or detoxify contaminants (e.g. petrol, herbicide)
- For natural materials, often achieved by stimulating activities of indigenous microorganisms
12
Q
Three outcomes for the pollutant molecule in bioremediation
A
- Minor change in molecule
- Fragmentation
- Complete mineralisation (organic –> inorganic)
13
Q
Bioremediation of hydrocarbons
A
- Organic pollutants
- Microbes have already been exposed to, or have been in contact with these compounds
- Have naturally evolved ways to degrade them
14
Q
Petroleum degradation
A
- Rich source of organic carbon
- Can be completely degraded to CO2
- Readily degraded by microbes where water and air are also present
- Degraded in both oxic and anoxic conditions
15
Q
Oxic degradation of petroleum
A
- Oxygenase enzymes are important
- Allows degradation on a reasonable time scale
16
Q
Anoxic degradation of petroleum
A
Very slow rate
17
Q
Large petroleum spills
A
- Volatile compounds evaporate
- non-volatile compounds remain (80% or more are oxidised within one year)
- Branched-chain and polycyclic hydrocarbons remain longer (difficult to biodegrade)
- Oil that gets into sediments is degraded very slowly with long term environmental impacts
18
Q
Oil oxidising microbes
A
- Develop rapidly on oil films and slicks
- Bacteria attach to oil droplets and decompose the oil
- Some bacteria grow only on hydrocarbons
- Some bacteria produce detergent that breaks up oil
19
Q
Factors that influence the rate of degradation of petroleum
A
- Temperature
- Nutrients (N + P)
- Predation
- Release of biosurfactants
20
Q
Xenobiotics
A
- Compounds not seen by microbes before
- Still organic compounds (contain C), just completely artificial
- Have chemical bonds that are “foreign” to microbes and therefore degraded very slowly if at all
- Highly chlorinated compounds are the most resistant to microbial degradation
- Some are co metabolised
21
Q
Examples of xenobiotics
A
Pesticides, dyes, chlorinated solvents, munitions, PCBs
22
Q
Co-metabolism
A
- Two substrates degraded simultaneously
- e.g. pesticide (secondary substrate) degraded only when organic matter (primary
substrate) is present - Sometimes co-metabolism generates toxic metabolites which kills the microbes
23
Q
DDT
A
- Highly chlorinated
- Organochloride
- Developed as a pesticide in the 1940s
- Bioaccumulates
24
Q
Aerobic dechlorination
A
Catalysed by dioxygenase enzyme
25
Q
Reductive dehalogenation
A
- Occurs in anoxic environment
- Uses chlorinated organic compound as electron acceptor
- Hydrogenolysis
- Dihaloelimination
- Yields organic compounds that can enter the citric acid cycle
26
Q
Hydrogenolysis
A
Halogen atom replaced by hydrogen
27
Q
Dihaloelimination
A
Two halogen atoms removed from adjacent carbon atoms, double bond formed between carbon atoms
28
Q
Plastics
A
- Polymers, most xenobiotics
- Polyethylene (plastic shopping bags) and polystyrene have carbon-carbon backbones (challenging to degrade)
29
Q
PET (pol(ethyleneterephthalate)
A
- Contains ester bonds
- Enzymes exist that degrade these bonds
30
Q
Ideonella sakaiensis
A
- Gram negative organism discovered in 2016
- Isolated from a consortium
- Uses two enzymes to degrade PET (PETase, MHETase)
31
Q
Wastewater health risks
A
- chemical intoxication / poisoning
- Spread of disease (cholera, hepatitis A)
32
Q
Wastewater treatment uses
A
- Physical and chemical methods, and
- Industrial scale use of microbes
33
Q
BOD
A
- Biological oxygen demand
- Efficiency of nutrient removal expressed as BOD
- Relative amount of dissolved O2 consumed by microbes to completely oxidise the organic matter
34
Q
COD
A
- Chemical oxygen demand
- Measures everything that can be chemically oxidised
35
Q
Primary wastewater treatment
A
- Physical separation methods
- Water passes through gates and screens
- Solids allowed to settle and effluent from top removed for further treatment
36
Q
Anaerobic secondary treatment
A
- Used for wastewater containing large quantities of
insoluble organic matter (high BOD) - Anaerobes digest suspended insoluble solids into soluble
components - These are fermented to fatty acids, H2, Co2
- Fatty acids fermented by syntrophic bacteria to acetate, CO2, H2
- Used by methanogens to make CH4, CO2
- CH4 burned or used as power
37
Q
Aerobic secondary treatment
A
- Used for wastewater with low levels of organic
matter (low BOD) - Uses oxidative degradation reactions
- Wastewater is mixed and aerated in large tanks
- Masses of bacteria called flocs form in water
38
Q
Flocs
A
- Oxidation of organic matter occurs on the floc as it is
mixed and exposed to air - Wastewater then pumped into holding tank, flocs
settle - Some of the settled flocs (activated sludge) returned to the aerator (as “inoculum”)
39
Q
Floc properties
A
- Oxic, anoxic, anaerobic zones
- Range of different microbial processes
- Range of metabolites produced
