The secret life of mites in the skin of our faces

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

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

The mites are transmitted during birth and are carried by nearly all humans, with numbers peaking in adults as the pores enlarge. They are about 0.3mm long, are found in the hair follicles of the face and nipples, including eyelashes, and eat the sebum naturally released by pore cells. They become active at night and move between follicles seeking to mate.

The first-ever genome sequencing study of the D. folliculorum mite has revealed that their isolated existence and resulting inbreeding causes them to shed unnecessary genes and cells and evolve into a transition parasites internal symbionts.

Dr Alejandra Perotti, associate professor of invertebrate biology at the University of Reading, who co-led the research, said: “We found that these mites have a different arrangement of body part genes compared to other similar species due to their adaptation to a protected life. inside the pores. These changes to their DNA resulted in unusual bodily characteristics and behaviors.

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

Close study of Demodex folliculorum DNA revealed:

  • Due to their isolated existence, with no exposure to outside threats, no competition to infest hosts, and no encounter with other mites with different genes, genetic reduction has caused them to become extremely simple organisms with tiny legs powered by only 3 unicellular muscles. They survive with the minimum protein repertoire – the lowest number ever observed in this and related species.
  • This genetic reduction is also the reason for their nocturnal behavior. Dust mites lack UV protection and have lost the gene that causes animals to wake up from daylight. They were also unable to produce melatonin – a compound that makes small invertebrates active at night – however, they are able to fuel their mating sessions all night long using melatonin secreted by human skin at dusk.
  • Their unique genetic disposition also results in unusual mating habits of the mites. Their reproductive organs have moved forward and the males have a penis that protrudes upwards from the front of their body, which means that they must position themselves below the female when mating and copulate both clinging to human hair.
  • One of their genes got inverted, giving them a particular arrangement of particularly protruding mouth appendages for collecting food. This facilitates their survival at a young age.
  • Mites have many more cells at a young age compared to their adult stage. This goes against the previous hypothesis that parasitic animals reduce their cell number early in development. The researchers say this is the first step for the mites to become symbionts.
  • Lack of exposure to potential mates who could add new genes to their offspring may have put the mites on a path to evolutionary deadlock and potential extinction. This has already been observed in bacteria living inside cells, but never in an animal.
  • Some researchers had assumed that the mites had no anuses and therefore had to accumulate all their excrement throughout their lives before releasing them when they died, causing inflammation of the skin. The new study, however, confirmed that they have anuses and have therefore been unfairly blamed for many skin conditions.
  • The secret life of mites in the skin of our faces

    The image shows the unusual position of the penis of a Demodex folliculorum mite. Credit: University of Reading

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

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

The research was carried out 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 is published in the journal Molecular biology and evolution.

Dr. Henk Braig, co-lead author from Bangor University and San Juan National University, said: “Mites have been blamed for many things. The long association with humans might suggest that they might also have simple but important beneficial roles. , for example, by keeping the pores of our face unclogged.”

New research on dust mites and respiratory infections

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

Provided by
Reading University

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