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[[File:GeoWikiWriteOff2021-Aljezen-Figure2.jpg|framed|center|{{figure number|2}} shows the mechanism to biodegrade hydrocarbons with the presence of oxygen.<ref name="6Das" />]]

[[File:GeoWikiWriteOff2021-Aljezen-Figure2.jpg|framed|center|{{figure number|2}} shows the mechanism to biodegrade hydrocarbons with the presence of oxygen.<ref name="6Das" />]]

The normal alkane (C₁-C₈ ''n''-alkane) in figure 2 will react with oxygen with the help of monooxygenase enzyme produced by living organisms (e.g. bacteria), and converts the normal alkane to an alcohol and oxidize iron from Fe2+ to Fe3+. Under aerobic conditions, simple aromatics such as benzene, xylene and toluene can be degraded.  Typically, this requires 3mg/L of dissolved oxygen to degrade 1 mg/L of these aromatics (i.e. 3:1 ratio).  If the dissolved oxygen content is lower than 3:1 then the biodegradation rate is slower.

The normal alkane (C₁-C₈ ''n''-alkane) in [[:File:GeoWikiWriteOff2021-Aljezen-Figure2.jpg|Figure 2]] will react with oxygen with the help of monooxygenase enzyme produced by living organisms (e.g. bacteria), and converts the normal alkane to an alcohol and oxidize iron from Fe²⁺ to Fe³⁺. Under aerobic conditions, simple aromatics such as benzene, xylene and toluene can be degraded.  Typically, this requires 3mg/L of dissolved oxygen to degrade 1 mg/L of these aromatics (i.e. 3:1 ratio).  If the dissolved oxygen content is lower than 3:1 then the biodegradation rate is slower.

Compared to aerobic degradation, anaerobic degradation is considered to proceed much slower This is because anaerobic pathways require more energy, i.e. they are energetically unfavorable. There are three different pathways that anaerobic microbes can utilize to biodegrade hydrocarbons. All three pathways require inserting an oxidizing group into the molecule, which makes it more active and thus easier to transform to microbial-consumable products such as fatty acids. The first pathway is called fumarate addition and this pathway is used by bacteria to activate C3 to C20 alkanes and alkyl-substituted aromatics such as xylene and toluene. The mechanism proceeds via addition to the double bond by terminal or pre-terminal alkyl group from the alkanes or alkyl-substituted aromatics then followed by the removal of a carbon dioxide molecule (fig.3) [7][8].  

Compared to aerobic degradation, anaerobic degradation is considered to proceed much slower This is because anaerobic pathways require more energy, i.e. they are energetically unfavorable. There are three different pathways that anaerobic microbes can utilize to biodegrade hydrocarbons. All three pathways require inserting an oxidizing group into the molecule, which makes it more active and thus easier to transform to microbial-consumable products such as fatty acids. The first pathway is called fumarate addition and this pathway is used by bacteria to activate C3 to C20 alkanes and alkyl-substituted aromatics such as xylene and toluene. The mechanism proceeds via addition to the double bond by terminal or pre-terminal alkyl group from the alkanes or alkyl-substituted aromatics then followed by the removal of a carbon dioxide molecule ([[File:GeoWikiWriteOff2021-Aljezen-Figure3.jpg|Figure 3).<ref name="7Fuchsetal">Fuchs, G., M/ Boll, and J. Heider, 2011, [https://www.nature.com/articles/nrmicro2652 Microbial degradation of aromatic compounds—from one strategy to four]: Nature Reviews Microbiology, v. 9, p.803–816.</ref><ref name="8Bianetal">Bian, X. Y., S, M. Mbadinga, Y. F. Liu, S. Z. Yang, J. F. Liu, R. Q. Ye, J. D. Gu, and B. Z. Mu, 2015, [https://www.nature.com/articles/srep09801 Insights into the anaerobic biodegradation pathway of n-alkanes in oil reservoirs by detection of signature metabolites]: Scientific Reports, v. 5. article no. 9801.</ref>

[[File:GeoWikiWriteOff2021-Aljezen-Figure3.jpg|thumbnail| Figure 3 shows the mechanism to activate hydrocarbons using Fumarate addition strategy.]]

[[File:GeoWikiWriteOff2021-Aljezen-Figure3.jpg|thumbnail| Figure 3 shows the mechanism to activate hydrocarbons using Fumarate addition strategy.]]

==References==

==References==

[7] Fuchs, G., Boll, M. and Heider, J., 2011. Microbial degradation of aromatic compounds-from

[7]  

[8] Bian, X.Y., Mbadinga, S.M., Liu, Y.F., Yang, S.Z., Liu, J.F., Ye, R.Q., Gu, J.D. and Mu, B.Z., 2015. Insights into the anaerobic biodegradation pathway of n-alkanes in oil reservoirs by detection of signature metabolites.

[8]  

[9] Heider, J., 2007. Adding handles to unhandy substrates: anaerobic hydrocarbon activation mechanisms.

[9] Heider, J., 2007. Adding handles to unhandy substrates: anaerobic hydrocarbon activation mechanisms.

[10] Boll, M., Loffler, C., Morris, B.E. and Kung, J.W., 2014. Anaerobic degradation of homocyclic aromatic compounds via arylcarboxyl-coenzyme A esters: organisms, strategies and key enzymes.

[10] Boll, M., Loffler, C., Morris, B.E. and Kung, J.W., 2014. Anaerobic degradation of homocyclic aromatic compounds via arylcarboxyl-coenzyme A esters: organisms, strategies and key enzymes.