Team:NAU-CHINA/Description
DESCRIPTION
BACKGROUND
INSPIRATION
SOLUTION
BACKGROUND
SELENIUM
Selenium (Se), a naturally occurring metalloid element, is essential to human and other animal health in trace amounts, yet harmful in excess. Of all the elements, selenium has one of the narrowest ranges between dietary deficiency (<40 mg/day) and toxic levels (>400 mg /day), which makes it necessary to carefully control intakes by human and other animals.
IN HUSBANDRY&
HUMAN HEALTH
According to research, selenium forms a vital constituent of the biologically important enzyme glutathione peroxidase (GPx), which acts as an antioxidant preventing oxidative cell degeneration. In accordance with these discoveries, selenium deficiencies in crops and livestock have been reported in all regions of the world.
Meanwhile, selenium deficiency is also implicated in the incidence of body disorders including Keshan disease, Kashin-Beck disease, thyroid disease, etc.
THREATS
Industrial areas dominated by coal mining, copper, zinc and other metal smelting activities are the main sources of selenium pollution. It is estimated that global man-made activities release 76,000-88,000 tons per year. In contrast, natural releases are only about 4,500 tons per year. If not properly handled, they will lead to serious environmental pollution.
When excessive amount of selenium is discharged into natural environment along with industrial activities, it will cause a severe damage to the water environment, especially fish. The figure shows the relationship between the selenium content in the water and the reproduction rate of fish. Failure rate of fish reproduction increases along with the increase of selenium content in water gradually. The widespread selenium pollution will harm not only fish, but also the whole eco-system eventually.
INSPIRATION
How shall we deal with the widespread poisonous selenite? Since some areas are contaminated by selenite while some are deficient in selenium, then why don’t we find a way to transform 4-valent selenium and 6-valent selenium, which are harmful to organisms, into 0-valent elemental eco-friendly selenium and apply it in the areas with selenium deficiency? Bingo! This is what we have done this year: alleviating selenium pollution through bioremediation.
As a promising method, bioremediation is both green and efficient, and has also been widely studied and applied to the treatment of pollutants. NAU-CHINA decided to choose this method and combine it with synthetic biology to use microorganisms to convert the pollutants selenite and selenate into selenium nanoparticles (SeNPs) that can be recycled by us.
According to literature, the desired product SeNPs obtained by pollutant treatment has the following characteristics:
①Nanoscale red elemental selenium
②Small particle size, high activity
③Low toxicity, more safe
④Protein and polysaccharide can enhance the stability of SeNPs
SOLUTION
In our project, we chose Escherichia coli BL21(DE3) as our chasis and successfully designed a genetic circuit containing two major modules to achieve our goal. One is flavoenzyme SsuE, which could help bacteria reduce selenite by providing reductive power. The other is SefA protein relevant to the assembly, helping to stabilize Se atoms and forming nanoscale complex with SefA protein.
After incubation, we lysed our engineered bacteria and lyophilized our products. Eventually, we got selenium nanoparticles-a kind of se-fertilizer, which stimulate the growth of plants successfully.
Many literatures show that SeNPs can not only be used in the traditional biomedicine, but also have a very broad application prospect in the electronics and optics industries because of their unique properties in photoelectricity, semiconductive theory, catalytic activities etc.
World Health Organization (1996) Trace elements in human nutrition and health. World Health Organization, Geneva.
Rotruck JT, Pope AL, Ganther HE, Swanson AB, Hafeman DG, Hoekstra WG (1969) Selenium: biochemical role as a component of glutathione peroxidase. Science 179:588–590.
Arthur J R, Beckett G J. Symposium 2 Newer aspects of micronutrients in at risk groups: New metabolic roles for selenium[J]. Proceedings of the Nutrition Society, 1994, 53(3): 615-624.
陈光玮. 硒还原菌对重金属/亚硒酸盐的处理特性与机理[D].大连理工大学,2020.
Lemly A D. Aquatic selenium pollution is a global environmental safety issue[J]. Ecotoxicology and Environmental Safety, 2004, 59(1):44-56.