The influx of high concentrations of organic matter associated with societal activity on land, large-scale aquaculture, and other activities may cause contaminated organic matter to deposit in the shallow seabed in coastal areas and worsen the seabed environment. There are methods of removing sediment, such as dredging work, in order to improve the seabed environment, but it is extremely difficult to remove all the sediment. Furthermore, in addition to disposal of the removed sediment, restoration of the coastal ecosystem and the material cycle also takes time.

Organic layers deposited on the seabed are oxygen depleted except for a small part of the upper layer that is in contact with the seawater, so anaerobic microorganisms are presumed to play an important role in the breakdown of this organic matter. However, the essence of anaerobic microorganisms and the mechanism of anaerobic ecosystem function restoration have not been clarified.

In collaboration with Ishinomaki Senshu University and the Tokyo University of Agriculture and Technology, researchers in AIST found a cooperative relationship (“a partnership”) between bacteria involved in the exchange of sulfur components in a seabed sediment washed up by the tsunami caused by the Great East Japan Earthquake. The seabed anaerobic ecosystem is restored during the process of the organic matter breakdown.

Organic layers deposited on the seabed are oxygen depleted except for a small part of the upper layer, so anaerobic microorganisms are responsible for the breakdown of organic matter. However, excessive influx of organic matter can cause the anaerobic ecosystem not to function adequately, leading to deterioration of the seabed environment (schematic left end).

This study showed that adding nitrate to seabed sediment with reduced breakdown function (schematic center left) resulted in formation of a cooperative relationship between sulfur-oxidizing bacteria and sulfate-reducing bacteria via the transfer of carbon sources (schematic center right), leading the activation of various anaerobic decomposition microorganisms (schematic right end).

This achievement elucidated for the first time the process by which the anaerobic ecosystem function of seabed sediment is restored, and is expected to greatly contribute to the establishment of the new conservation and management technologies for the coastal seabed.