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The secret lives of mites in the skin of our faces

The secret life of mites in the skin of our face

Image showing Demodex folliculorum mite on the skin under Hirox microscope. Credit: University of Reading

Microscopic mites that live in human pores and mate at night on our faces are becoming such simplified organisms due to their unusual lifestyles that they may soon become one with humans, new research finds.

The mites are passed on during birth and are carried by almost every human being, peaking in adults as the pores enlarge. They are about 0.3 mm long, are found in the hair follicles on the face and in the nipples, including the eyelashes, and eat the sebum naturally released by cells in the pores. They become active at night and move between the follicles to mate.

The first-ever genome sequencing study of the D. folliculorum mite found that their isolated existence and resulting inbreeding causes them to reject unnecessary genes and cells and move from external parasites to internal symbionts.

dr. Alejandra Perotti, associate professor of invertebrate biology at the University of Reading who co-led the study, said: “We found that these mites have a different arrangement of body part genes than other similar species because they adapt to a sheltered life. within the pores. These changes in their DNA have resulted in some unusual body characteristics and behaviors.”

Demodex folliculorum mite walking under a microscope. Credit: University of Reading

The in-depth study of the Demodex folliculorum DNA revealed:

  • Due to their isolated existence, with no exposure to external threats, no competition to infect hosts, and no encounters with other mites with different genes, genetic reduction has made them extremely simple organisms with tiny legs powered by only 3 single-celled muscles . They survive on the minimal repertoire of proteins — the lowest number ever seen in this and related species.
  • This gene reduction is also the reason for their nocturnal behavior. The mites lack UV protection and have lost the gene that causes animals to wake up in daylight. They are also incapable of producing melatonin — a compound that makes small invertebrates active at night — but they can feed their nocturnal mating sessions on the melatonin secreted by human skin at dusk.
  • Their unique gene arrangement also results in the mites’ unusual mating habits. Their reproductive organs have moved forward and males have a penis that protrudes upward from the front of their bodies meaning they have to position themselves below the female when mating, and copulate while both clinging to the human hair.
  • One of their genes is reversed, giving them a particular arrangement of mouth appendages that protrude mainly for food-gathering. This promotes their survival at a young age.
  • The mites have many more cells at a young age than in their adult stage. This goes against the previous assumption that parasitic animals reduce their cell numbers early in development. The researchers argue that this is the first step in turning the mites into symbionts.
  • The lack of exposure to potential mates who can add new genes to their offspring may have set the mites on course for an evolutionary dead end and possible extinction. This has been seen before in bacteria living in cells, but never in an animal.
  • Some researchers assumed that the mites do not have an anus and therefore must collect all of their feces throughout their lives before releasing it when they die, causing skin inflammation. However, the new study confirmed that they have anus and are thus wrongly blamed for many skin conditions.
  • The secret life of mites in the skin of our face

    Image shows unusually positioned penis of a Demodex folliculorum mite. Credit: University of Reading

  • The secret life of mites in the skin of our face

    Microscope view of the posterior end of the anus of a Demodex folliculorum mite. The presence of an anus on this mite had previously been mistakenly overlooked by some, but this study confirmed its presence. Credit: University of Reading

The research was led by the University of Bangor and the University of Reading, in collaboration with the University of Valencia, the University of Vienna and the National University of San Juan. It has been published in the magazine Molecular biology and evolution

dr. Henk Braig, co-lead author of the University of Bangor and the National University of San Juan, said: “Mites have been blamed for many things. Their long association with humans could indicate that they can also play a simple but important beneficial role. play, for example by keeping the pores in our faces closed.”

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More information:
Gilbert Smith et al, Human follicular mites: ectoparasites become symbionts, Molecular biology and evolution (2022). DOI: 10.1093/molbev/msac125

Provided by the University of Reading

Quote: The Secret Life of Mites in the Skin of Our Faces (2022, June 21) Retrieved June 21, 2022 from https://phys.org/news/2022-06-secret-mites-skin.html

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