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Alkane Biodegradation
R. A. Kerr Science 329, 734-735 (2010)
Alkanes
Alkane Formula Boiling point [°C]
Melting point [°C] Solubility at 20 °C
Methane CH4 -162 -182 gas
Ethane C2H6 -89 -183 63.7 gas
Propane C3H8 -42 -188 gas
Butane C4H10 0 -138 gas
Hexane C6H14 69 -95 12.3 liquid
Octane C8H18 126 -57 liquid
Nonane C9H20 151 -54 liquid
Decane C10H22 174 -30 0.05 liquid
Dodecane C12H26 216 -10 liquid
Hexadecane C16H34 287 19 5.2 x 10 -5 liquid
Icosane C20H42 343 37 3.1 x 10 -7 solid
Triacontane C30H62 450 66 solid
Tetracontane C40H82 525 82 solid
Pentacontane
C50H102 575 91 solid
Hexacontane C60H122 625 100 solid
• 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
n-alkane aerobic degradation pathways
Callaghan 2006, Biodegradation 1990 1:79-92-oxidation
-oxidation
OH
H
O
OH
O
OHOH
O
OHH
O
O
OHOH
O
O
OH
O
H
OOH
OH
O
O
O
O
O
OH
O
OH+
Diterminal oxidation Terminal oxidation Subterminal oxidation
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
http://www.nies.go.jp/kenko/biotech/bioehp/Topics1.html
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)
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_unit_on_fire_2010.jpg April 21, 2010
http://1.bp.blogspot.com/_1p20WdeXKKs/TD-VPBQ7NuI/AAAAAAAAJao/7a_bs38l5jE/s200/GulfOilSpillCap1.jpg
Deepwater Horizon-physical/chemical remediation
• Burning – not environmentally smart – greenhouse gases, toxic chemicals released into the atmosphere
• 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://advocacy.britannica.com/blog/advocacy/2010/06/catastrophe-in-the-gulf-2/
http://www.csmonitor.com/USA/2010/0530/BP-oil-spill-top-kill-failure-means-well-may-gush-until-August
http://beforeitsnews.com/story/99/939/What_Is_The_Corexit_Dispersant.html
E. Kintisch Science 329, 735-736 (2010)
Adding dispersant to gushing oil
Oil washing up in wetland area
Studying the spill
http://oceanexplorer.noaa.gov/explorations/03windows/logs/jul24/media/pushcorealvin.html
Sample collection
http://www.whoi.edu/dwhresponse/page.do?pid=43715&tid=201&cid=44272&ct=362#
http://www.whoi.edu/oceanus/viewSlideshow.do?clid=58913&aid=105249&mainid=159855&p=157273&n=159853
http://www.mpg.de/257961/Oil_degrading_bacteria?print=yes
• 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
Biodegradation concerns
Oil-degrading microbes• 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
Image from Hoi-Ying Holman group)
Oil consuming bacteria on oil droplets, 1500x magnification © Johannes Zedelius, MPI Bremen
Results
http://www.msnbc.msn.com/id/21134540/vp/38853793#38853793