Registration Dossier

Environmental fate & pathways

Additional information on environmental fate and behaviour

Administrative data

Endpoint:
additional information on environmental fate and behaviour
Adequacy of study:
supporting study
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
other: peer reviewed international scientific journal

Data source

Reference
Reference Type:
publication
Title:
Degradation of alkanes by bacteria
Author:
Rojo, F.
Year:
2009
Bibliographic source:
Environmental Microbiology, 11: 2477–2490. doi: 10.1111/j.1462-2920.2009.01948.x

Materials and methods

Test guideline
Qualifier:
no guideline required
Type of study / information:
The publication summarises the current mechanistic knowledge on how microorganisms degrade alkanes, providing details of the biochemical pathways involved and how the expression of pathway genes is regulated and integrated within cell physiology.

Results and discussion

Applicant's summary and conclusion

Conclusions:
Linear and branched alkanes spanning the carbon number range of members of the Category "Hydrocarbons, C14 -C20, aliphatics (<2% aromatics)” are aerobically and anaerobically biodegradable. Branched-chain alkanes are more difficult to degrade, however, several bacterial strains can degrade them nevertheless.
Executive summary:

Linear and branched alkanes spanning the carbon number range of members of the Category "Hydrocarbons, C14 -C20, aliphatics (<2% aromatics)” are aerobically and anaerobically biodegradable. Branched-chain alkanes are more difficult to degrade, however, several bacterial strains can degrade branched-chain alkanes (such as isooctane).

Many microorganisms (bacteria, filamentous fungi and yeasts) can degrade alkanes, using them as the carbon source. A typical soil, sand or ocean sediment contains significant amounts of hydrocarbon-degrading microorganisms, and their numbers increase considerably in oil-polluted sites.

Alkanes are also produced by many living organisms such as plants, green algae, bacteria or animals. This probably explains why alkanes are present at low concentrations in most soil and water environments.

Various alkane degraders are bacteria that have a very versatile metabolism, so that they can use as carbon source many other compounds in addition to alkanes. Most frequently, alkanes are not preferred growth substrates for these bacteria, which will rather utilize other compounds before turning to alkanes. On the other hand, some bacterial species are highly specialized in degrading hydrocarbons. They are called hydrocarbonoclastic bacteria and play a key role in the removal of hydrocarbons from polluted environments.

Under strictly anaerobic conditions alkanes have to be activated through a mechanism that does not rely on O2. There are several bacterial strains able to use alkanes as carbon source in the absence of O2; these microorganisms use nitrate or sulfate as electron acceptor. Growth is significantly slower than that of aerobic alkane degraders. However, anaerobic degradation of alkanes plays an important role in the recycling of hydrocarbons in the environment. The strains analysed normally use a narrow range of alkanes as substrate. For example, strain BuS5, a sulfate-reducing bacteria that belongs to the Desulfosarcina/Desulfococcus cluster, assimilates only propane and butane or Azoarcus sp. HxN1, a denitrifying bacteria, uses C6–C8 alkanes, while Desulfobacterium Hdx3 metabolizes C12–C20 alkanes.