Question

Microbiology question.

The methane- oxidizing bacteria are often involved in marine mutualisms whilist the methanogen archaeal bacteria are only rarely involved. Explain the origin of methane in the marine environments and using examples, explain the evidence for the truth or falsehood of the above statement.

Answer 1

The existence of methane in the ocean is the consequence of the balance between the enormous methane additions from continental shelf and slope sediments and the microbial oxidation reactions that must occur in sediments and the water to produce the low concentrations observed in the bulk of the ocean volume.

A poor number of external sources contribute methane to the ocean . The source processes includes:

- microbially- mediated diagenesis of sediment organic matter,

- abiotic production of methane through the serpentinization reaction : a rock/water reaction occurring in hydrothermal systems associated with the mid ocean ridges and spreading centers

- leaks from near-surface petroleum deposits

-decomposition of methane clathrate hydrates

So, many of the ocean methane is produced in sediments and has a benthic source. Methane is oxidized under anoxic conditions in marine sediments and waters and under aerobic conditions at the benthic boundary layer and in the bulk of water.

Biological production of methane or methanogenesis is the last step in the remineralization of complex organic matter in anaerobic systems.

Organic matter degradation involves a sequence of reactions in which complex organic matter is hydrolyzed to monomers and these are fermented to hydrogen, low molecular weight fatty acids, alcohols, and methylated compounds.

Methanogens require simple molecules as substrate, the most important being hydrogen  and acetate, and are dependent on the activities of other microorganisms to provide these substrates

One example of open-ocean methanogenesis involves anoxic digestive tracts and fecal pellet micro environments; methane released during fecal pellet disaggregation results in the mixed-layer methane maximum. However, the bulk of the methane in the ocean is added by outside sources than microbial origin

Decomposition of methane is mediated by two biological processes:

• anaerobic oxidation of methane by bacteria and archaea (formerly called archaebacteria) within the sea floor;
• aerobic oxidation of methane by bacteria in the water column

The high concentration of Methane in the ocean surface is the result of the complex ways that bacteria break down dissolved organic matter, a cocktail of substances excreted into seawater by living organisms.