A research group at Tohoku University has discovered a new type of microorganism that parasitizes plankton, which causes "shellfish poisoning" that causes numbness and dyspnea when eating shellfish, and has the function of removing it.
It is expected that it will lead to technology to reduce damage.
Shellfish poison is the accumulation of toxins in the body of bivalves that ate toxic plankton. Of these, "parasitic shellfish poison" causes symptoms such as numbness in limbs, headache, and dyspnea, and dies. Sometimes.
As a result of a detailed analysis of seawater in Osaka Bay by a research group of Associate Professor Go Nishitani of the Graduate School of Agriculture, Tohoku University, a new species that parasitizes toxic plankton that causes paralytic shellfish poisoning and has the function of removing it. I found a bacterium.
It is a kind of microorganism called "Amebofuria", and when it enters the cell from the surface of plankton, it grows up to hundreds and the parasitized plankton disappears in 2 to 3 days.
According to a survey in Osaka Bay, more than 70% of toxic plankton that reached the peak of reproduction were infested with this microorganism and almost disappeared in 1 to 2 weeks. It means that it does not parasitize phytoplankton such as.
The number of cases where shellfish poisoning exceeding the standard is detected by inspections conducted by prefectures and the shipment of shellfish is restricted is increasing in Miyagi and Iwate prefectures, so the research group is increasing the number of microorganisms and sowing them in the sea. So, I hope that the damage and impact can be reduced.
Associate Professor Nishitani says, "We will confirm the safety and effectiveness of the product with the aim of putting it into practical use, and with the cooperation of fishermen, we would like to start testing in the sea within three years."
How to extinguish toxic plankton
In a microscope image of a newly discovered microorganism parasitizing and extinguishing toxic plankton, which causes shellfish poisoning, when the microorganism attaches to toxic plankton, it invades cells and proliferates. To go.
At the end, you can see how the number of microorganisms increases from 300 to 400, hijacks plankton, breaks through from the inside, and spreads to the surroundings.
The liquid, which has been cultivated with toxic plankton and increased in large quantities, becomes turbid brown and looks like red tide.
After about a week of adding the discovered microorganisms to this liquid, it became colorless and transparent, indicating that plankton had disappeared.
Associate Professor Nishitani points out that "when microorganisms parasitize, they can grow at an astonishing rate and remove plankton."
Paralytic shellfish poisoning is a serious problem in the fishery industry
According to the Fisheries Research and Education Agency and the Ministry of Health, Labor and Welfare, paralytic shellfish poisoning occurs in each sea area from Hokkaido to Okinawa, but in recent years the range has tended to expand and the period has become longer, and the fishery industry Is a serious problem.
Taking the Seto Inland Sea as an example, paralytic shellfish poisoning was reported mainly in the western sea area every year, but in recent years it has also been confirmed in the eastern sea area such as Osaka Bay and Harima Nada. am.
In addition, the period during which shellfish poisoning occurs is longer, and it is said that it usually occurs around the end of April when the seawater temperature rises and subsides when the water temperature becomes cold, but in recent years shellfish poisoning has occurred from around February. It is being reported, and it tends to prolong the period when it cannot be shipped.
It is said that there are no measures to prevent the outbreak of shellfish poisoning, and if an outbreak is confirmed, measures are taken to limit shipping.
Mr. Masami Hamaguchi of the Fisheries Research and Education Agency said, "The damage caused by shellfish poisoning is becoming more serious for aquaculture companies every year. Since it has been said that there is no countermeasure so far, this result may be an effective countermeasure. It is expected that there will be. "
In Miyagi prefecture, it has been increasing since the Great East Japan Earthquake.
The number of cases in which shellfish poisoning exceeding the national standard value was detected in each sea area of Miyagi Prefecture and self-regulation of shipments was carried out has continued to increase for several years, and the period of regulation tends to be prolonged.
According to the summary of Miyagi prefecture, the number of cases where self-regulation of shipments due to the detection of shellfish poison was previously about 10 cases a year, but it has been increasing since around 2011 when the Great East Japan Earthquake occurred.
In 2018, there were 26 cases, exceeding 20 cases for the first time since 1992, when records remain, and the number of cases increased further to 37 cases.
Last year, there were 29 cases.
Previously, it was said that when the water temperature became low, the occurrence of plankton, which was the cause, subsided, but recently shellfish poisoning may be detected even in winter, and the shipping restriction period for scallops etc. is 200 days. The above cases are occurring one after another.
Regarding this background, Miyagi Prefecture points out that it is possible that plankton, which causes shellfish poisoning, has risen from the seabed and has been activated by the tsunami caused by the Great East Japan Earthquake.