Alkane Biodegradation
R. A. Kerr Science 329, 734-735 (2010)
Alkanes
•
•
•
•
•
Saturated hydrocarbons
Large fraction of crude oil
Solubility decreases with chain
length (straight chains)
Can also be branched chains or
rings
Branched chains are more
difficult to degrade than straight
chains
CH4
C2H6
C3H8
C4H10
Boiling
point [°C]
-162
-89
-42
0
Melting
point [°C]
-182
-183
-188
-138
Hexane
C6H14
69
-95
Octane
C8H18
126
-57
liquid
Nonane
C9H20
151
-54
liquid
Decane
C10H22
174
-30
Dodecane
C12H26
216
-10
Hexadecane
Icosane
C16H34
C20H42
287
343
19
37
Triacontane
C30H62
450
66
solid
Tetracontane C40H82
525
82
solid
Pentacontane C50H102
575
91
solid
Hexacontane C60H122
625
100
solid
Alkane
Formula
Methane
Ethane
Propane
Butane
Solubility
63.7
12.3
0.05
at 20 °C
gas
gas
gas
gas
liquid
liquid
liquid
5.2 x 10 -5
3.1 x 10 -7
liquid
solid
n-alkane aerobic degradation pathways
Subterminal oxidation
Terminal oxidation
Diterminal oxidation
OH
OH
O
O
H
OH
H
O
O
OH
O
OH
O
O
HO
O
OH
O
H
O
OH
-oxidation
O
O
O
HO
OH
OH
HO
+
O
O
-oxidation
Callaghan 2006, Biodegradation 1990 1:79-92
Aerobic degradation
http://2010.igem.org/Image:TUDelft_Alkane_degradation_route.png
• Oxygen-dependent reactions
• Formation of fatty acids, followed by β-oxidation
• Biosurfactants may be required before degradation can begin
Branched alkanes
• More difficult to degrade
than n-alkanes
Appl. Environ. Microbiol. 2000;66:4462-4467
Alkane biodegradation-anaerobic
Environ. Microbiol. 2009 11(10):2477-2490
β-oxidation
http://nutrition.jbpub.com/resources/animations.cfm?id=23&debug=0
Bioremediation
Bioremediation – using
biological systems to treat
contaminated sites
Biodegradation – biological
activity that results in the break
down of a specific contaminant
Bioaugmentation – adding
biodegrading organisms to the
contaminated site (not
genetically manipulated)
http://www.nies.go.jp/kenko/biotech/bioehp/Topics1.html
Biostimulation – adding
nutrients like nitrogen or
phosphorus in order to
stimulate microbial activity
Case study: Deepwater Horizon
• Louisiana crude oil
• Predominantly alkanes, lower
concentrations of aromatics
• Oil in a large plume near the
wellhead, 1 km depth
• Also surface oil, mobilized oil,
reaching shoreline/sensitive
wetland areas
http://en.wikipedia.org/wiki/File:Deepwater_Horizon_offshore_drilling_u
nit_on_fire_2010.jpg April 21, 2010
http://1.bp.blogspot.com/_1p20WdeXKKs/TDVPBQ7NuI/AAAAAAAAJao/7a_bs38l5jE/s200/GulfOilSpillCap1.jpg
Deepwater Horizon-physical/chemical
remediation
• Burning – not environmentally smart –
greenhouse gases, toxic chemicals released
into the atmosphere
http://advocacy.britannica.com/blog/advocacy/2010/06
/catastrophe-in-the-gulf-2/
• Physical removal-does not remove all of the
oil; there is water recovered as well, would
need to be separated from the oil
• Chemical dispersion
http://www.csmonitor.com/USA/2010/0530/BP
-oil-spill-top-kill-failure-means-well-may-gushuntil-August
http://beforeitsnews.com/story/99/939
/What_Is_The_Corexit_Dispersant.ht
ml
Oil washing up in wetland area
Adding dispersant to gushing oil
E. Kintisch Science 329, 735-736 (2010)
Studying the spill
Sample collection
http://www.whoi.edu/oceanus/viewSlideshow.do?clid=58913&aid=105249&mainid=159855&p=157273&n=159853
http://www.whoi.edu/dwhresponse/page.do?pid=43715&tid=201&cid=44272&ct=362#
http://oceanexplorer.noaa.gov/explorations/03windows/logs/jul24/media/pushcorealvin.html
Biodegradation concerns
• Bioavailability:
– Bacteria are located at the oil-water interface, not inside the oil droplets
– Smaller droplets (dispersed oil) give more surface area to increase
biodegradation.
• Explosions in bacterial growth would deplete available
nutrients and ultimately slow degradation
• Oxygen consumption – possible dead zones?
• Sedimentation – deposition in anaerobic zones in sediment
http://www.mpg.de/257961/Oil_degrading_bacteria?print=yes
Oil-degrading microbes
Image from Hoi-Ying Holman group)
• Hazen et al. (2010) found 2-fold higher cell
densities within the plume.
• Enrichment in plume for Oceanospirillales
• Some oxygen depletion in the plume, not
enough to create anoxic “dead zones”
• Enough oxygen loss to indicate aerobic
activity
• Increased degradation genes in plume
• Valentine et al. (2010) found
oxygen depletion in the plume to
be driven by ethane and propane
metabolism
Oil consuming bacteria on oil droplets, 1500x magnification © Johannes Zedelius, MPI Bremen
Results
http://www.msnbc.msn.com/id/21134540/vp/38853793#38853793