The Ecology of Humans (2) Microbiome


The human body and its symbionts can be viewed as a community of interacting cells. ~ American microbiologist and immunologist David Relman et al

The human body is a rich ecosystem: a vast collective of microbial life. People lug around 10 times as many microbes as they have cells – the little ones are hard to tally.

A developing fetus get its 1st microbiome from its mother. From the moment you were born, every exposed surface and organ of the body has attracted microbes.

At the cellular level, a human is a world unto itself. Our bodies are in symbiotic relationships with microbes to accomplish most everything a mind-body does.

The human-microbial ecosystem plays a variety of important roles in human health and disease. ~ American microbiologist and immunologist Elizabeth Costello

There is a continuous intimate dialogue between body and microbiome. Microbial missives direct bodily development and functioning, including influencing desires. Conversely, host cell communication impacts the activities and populations of microbial communities within the body.

The mind can affect the microbiome and the microbiome can affect the mind. ~ American microbiologist Laura Sanders

Much of the microbiome comprises viruses and bacteria, but there are also protists and multicellular species, such as fungi. Then there are the parasites and pathogens, both internal (e.g., flukes) and on the skin (e.g., lice).

Eyelash mites are ubiquitous on adults, and common on children. These mites are snugly tucked into the sebaceous glands connected to hair follicles. They are permanent residents and cannot be washed off.

Microbiota are instrumental in defining the quality of its host’s life. The microbiome is personalized, localized, and specialized.

Even before birth, one’s microbiome is a determinant of health, and remains so throughout life. Changing diet can alter the ecosystem of gut microbiota within a matter of days.

Commensal microbes offer genes that complement the human genome in many ways, including such basic functions as metabolism. Microbes are critical for enzyme production. Our bodies possess a pathetic complement of enzymes whereas microbes carry an arsenal.

Mitochondria monitor the health of their cells. When stressed by lack of nutrition or pathogenic attack they initiate corrective responses. Among them are enlisting the assistance of local microbes. That the mitochondrion genome is related to bacterial genomes is conducive to communicating and coordinating activities.

There is an intricate interdependence among the many thousands of microbial colonies within the body. The human body comprises a metagenome of all its constituent life. The 1,000 species or so microbial species in the human digestive tract present 100 times as many genes as the human genome has. This is one reason that the quality of microbiome bodes for the health of its host. If microbiotic diversity is low, the toolkit for fighting infections is meager.

A few microbes interested in humans make people sick but most are commensal and call our body their home. Even unwelcome ones can be helpful. An established herpes virome in a human makes the body less susceptible to certain bacterial infections. More generally, resident viruses are instrumental in modulating metabolism and health. When the bacterial gut flora ecosystem is disrupted, such as by antibiotics, resident viral communities step up to protect the host from infection.