don’t rule the planet. Humans don’t even rule their own
bodies. During the past 20 years or so, it’s become apparent
that the guys in charge of everything are a nanometer across
and run in packs, or perhaps more accurately, hang out in
mobs. These gangs of microorganisms are together referred to
as the microbiome, and we’re just beginning to understand
what these worlds within our world do to us and for us.
little data, according to "Dirt Is Good," a recent
book by Jack Gilbert, director of the University of Chicago
Microbiome Center, and Rob Knight, director of the University
of California Center for Microbiome Innovation, with science
writer Sandra Blakeslee:
outnumbered. Microbes outweigh all visible plants and animals
on earth by a factor of 100 million. The total number of
bacteria alone is a 1 with 30 zeroes after it: a nonillion.
For the total number of viruses, add two zeroes to those 30.
inexperienced. Microbes ran everything without an assist from
humans, fish, ferns or even trilobites for about 3 billion of
the last 4.5 billion years.
a minority even in your own skin. For every one of your cells,
there are 1.3 microbial cells in your body. About 30 trillion
cells are yours; another 40 trillion cells in your body are
microbes. Together, those microbes weigh as much as your brain
— 3 pounds — and have an astonishing influence on that
organ, to say nothing of the sway they hold on your digestive
tract, your urogenital system and your immune system.
point, it’s an old joke but true: When the American poet
Walt Whitman wrote, "I contain multitudes," he wasn’t
kidding. ("I Contain Multitudes" is also a 2016 book
about the microbial world by science writer Ed Yong. )
the existence of this microbial universe has never been a
secret, until fairly recently, scientists had little access to
its mysteries. Scientific scrutiny was limited to microbes
that would grow in a laboratory, a remarkably teeny sample.
What changed everything was the development of a technique to
sequence microbial DNA directly from the environment. Pair
that newfound ability with the rapid drop in the cost of
genetic sequencing, and the field took off. "So what
would have cost you $100 million 15 years ago costs you 100
bucks now, so there’s a whole lot that we can do,"
Knight said in a phone interview.
instance, science can now answer this riddle: Your baby hurls
his pacifier onto the kitchen floor. To protect your infant’s
health, which is the best way to clean it?
the pacifier under hot water.
the pacifier in your mouth, swish it around, then give it back
to your pitcher-in-training.
answered A, who can blame you?
"Dirt Is Good" authors Knight and Gilbert would
disagree. Their book examines how to raise healthy kids by
leveraging what we know about our microbial overlords.
mouth is full of antimicrobial peptides, full of good bacteria
producing all these things to fight off the bad
bacteria," Knight said. Mom swishes the pacifier in her
mouth, coats it with these germ-fighting peptides, and
provides her kid a gift of beneficial bacteria. Whereas the
bacteria in tap water? They’re not on your team. They’re
unlikely to hurt you, but they’re not designed to fight
human diseases that the mom’s immune system is.
shows we’re not only filled with these microbes; every hour,
we shed clouds of them, a million particles of bacteria,
fungi, viruses and the single-cell, nucleus-lacking members of
the kingdom Archaea. Researchers at the University of Oregon
found that our microbial shedding creates a near fingerprint,
leading researchers in the forensic sciences to explore
whether the bacteria left at a crime scene might someday be
used to identify bad guys.
should be clear by now that we’re not talking about bacteria
as invaders; we’re talking about a polyamorous exchange with
single-cell life partners that interact intimately with our
immune system, affect our moods and mental health, and
contribute to the regulation of our metabolisms, playing roles
in obesity and Type 2 diabetes, and even driving our food
no prescription, no exact formula to cultivate a microbiome
that will, for example, prevent sugar cravings and diabetes,
but several behaviors will enhance the survival of the best
bugs, Knight said. For instance, exercise may foster
beneficial gut bacteria populations. In mice, exercise reduces
bacterial species that cause inflammation while increasing
anti-inflammatory species. High fiber foods starve
less-supportive bacteria and boost healthy types. Bacteria
that ferment dietary fiber produce short-chain fatty acids.
These fatty acids can reduce insulin resistance, a precursor
of Type 2 diabetes.
you’re eating a diverse diet, especially with lots of
different kinds of fruits and vegetables, and with fermented
foods, that’s been shown to have a restorative effect"
on the health of your gut microbiome, Knight said. Fermented
foods include yogurt, pickles and kimchi — all have species
of the helpful bacteria Lactobacillus.
health appears to play a role in brain health, a growing
number of studies suggest. In one small study, children with
autism who received fecal microbiota transplants showed
reduced digestive complaints and improved communication and
socialization skills. Although the study was too limited to
provide definitive evidence, it’s promising, Knight said.
in the gut talk to the brain in several ways: They produce
neurotransmitters — including 90 percent of the body’s
serotonin, Knight said. They manufacture small molecules that
float through the blood stream controlling which genes are
turned on and which are turned off. They activate the immune
system, which affects the brain. Finally, they can direct-dial
through the gut’s vagus nerve — a line straight to the
Canadian study showed a Lactobacillus-based probiotic cured
depression in mice. But when the vagus nerve was clipped, the
mouse depression remained. A vagus-brain connection was also
suggested in a large epidemiological study that found a
reduced risk of Parkinson’s disease with partial vagal nerve
removal. Parkinson’s patients have a distinctive gut
microbiome compared with healthy controls, according to a
study released earlier this year.
good to help children grow a protective microbiome. For that,
Knight and Gilbert have an easy answer: dirt. Kids with dogs,
for instance, have a 13 percent reduced risk of asthma.
Children on farms do even better, with a 50 percent reduced
risk, they report.
we’re starting to find out is exposure to natural healthy
bacteria in the environment is really important for training
our immune system and making sure it doesn’t go really
haywire and attack us," Knight said.
Knight and Gilbert write, "Get (kids) outside, let them
interact with animals, allow them to play in the dirt, rivers,
streams, ocean. Don’t sterilize everything they are going to
touch or put in their mouth."
kid, it seems, is a healthy one.