Cholesterol and phytosterol are sterols, essential fatty compounds for many biological processes such as the functioning of cell membranes. Until now, it has been assumed that phytosterols are characteristic of plants and cholesterol of animals, and that only plants can produce phytosterols, whereas animals usually produce cholesterol. Dolma Michellod, Nicole Dubilier and Manuel Liebeke of the Max Planck Institute for Marine Microbiology in Bremen, Germany, were surprised when they discovered that a small marine worm called Olavius algarvensiswhich lives in the seagrass beds of the Mediterranean, has much more phytosterol than cholesterol.
“We knew that the worms couldn’t be eating the seagrass because they don’t have a mouth or gut,” explains first author Michellod. “We then asked if the symbiotic bacteria inside olavio, which provides them with their nutrition, could produce phytosterols, but this was not the case,” adds Dubilier. “We were also able to exclude that the worms were taking up phytosterols through the skin. That’s when we realized that the worms must be producing the phytosterols themselves,” Liebeke explains.
The Max Planck researchers, together with colleagues from MARUM (Center for Marine Environmental Sciences in Bremen), the University of Münster, the University of Hamburg, North Carolina State University and Imperial College London, used a large number of methods that included sequencing of the worm’s DNA and RNA, protein and metabolite analysis, and sterol imaging to reveal that it is the worm that produces the phytosterols, and that the main phytosterol they produce is sitosterol. Their study is the first to show that a metazoan animal can synthesize phytosterols and was published in the journal Science May 5he.
From worms to corals: Five phyla of animals have the genes to produce phytosterols
Even more surprising to the researchers was their discovery that the gene needed to produce sitosterol from cholesterol precursors is widespread in the animal kingdom. “We discovered a gene that was thought to have been lost a long time ago in animal evolution,” explains Liebeke. Michellod adds: “It was exciting to discover this gene in so many different groups of animals, from corals and earthworms to clams and mussels.” “This means that there is a strong selective advantage for animals in having the gene that allows them to make phytosterols. We think that phytosterols could make animal membranes more permeable, but so far, that’s just wild speculation.” Dubilier.
The good, the bad, and the ugly: understanding the role of cholesterol and phytosterols
Until now, sterol research in animals has focused on cholesterol. Known for being “the good, the bad, and the ugly,” some forms of cholesterol are essential for building cell membranes and producing hormones, while others are harmful and can block blood vessels and increase the risk of cardiovascular disease. A host of recent findings on the benefits of phytosterols for humans indicate that they can improve blood cholesterol levels, thereby reducing the risk of heart attack or stroke. But the precise way in which phytosterols provide benefits is far from understood. Researchers at the Max Planck Institute for Marine Microbiology are convinced that the tiny marine worm Olavius algarvensis is a valuable model organism to better understand the beneficial role of plant sterols for animal health and welfare.
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