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Bacteria - the essential form of life

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{Nature_and_Environment.123.13}: Jay Hoffman {resist} Tue, 17 Dec 2019 19:20:21 CST (76 lines)

The ratio of bacteria cells in humans is closer to 3 to 2 than 10 to 1

It's often said that the bacteria and other microbes in our body
outnumber our own cells by about ten to one. That's a myth that should
be forgotten, say researchers in Israel and Canada. The ratio between
resident microbes and human cells is more likely to be one-to-one,
they calculate.

A 'reference man' (one who is 70 kilograms, 20–30 years old and 1.7
metres tall) contains on average about 30 trillion human cells and 39
trillion bacteria, say Ron Milo and Ron Sender at the Weizmann
Institute of Science in Rehovot, Israel, and Shai Fuchs at the
Hospital for Sick Children in Toronto, Canada.

Those numbers are approximate — another person might have half as many
or twice as many bacteria, for example — but far from the 10:1 ratio
commonly assumed.

The 10:1 myth persisted from a 1972 estimate by microbiologist Thomas
Luckey, which was “elegantly performed, yet was probably never meant
to be widely quoted decades later”, say the paper’s authors. A
particular overestimate in Luckey’s work relates to the proportion of
bacteria in our guts, but most bacteria reside only in the colon
(which has a volume of 0.4 litres).

Putting together these kinds of calculations, the researchers produce
a ratio for microbial to human cells for the average man of 1.3:1,
with a wide uncertainty.

"https://www.nature.com/news/scientists-bust-myth-that-our-bodies-
have-more-bacteria-than-human-cells-1.19136"


More than half your body is not human

Human cells make up only 43% of the body's total cell count. The rest
are microscopic colonists.
Understanding this hidden half of ourselves - our microbiome - is
rapidly transforming understanding of diseases from allergy to
Parkinson's.

The field is even asking questions of what it means to be "human" and
is leading to new innovative treatments as a result.

"They are essential to your health," says Prof Ruth Ley, the director
of the department of microbiome science at the Max Planck Institute,
"your body isn't just you".

No matter how well you wash, nearly every nook and cranny of your body
is covered in microscopic creatures.

This includes bacteria, viruses, fungi and archaea (organisms
originally misclassified as bacteria). The greatest concentration of
this microscopic life is in the dark murky depths of our oxygen-
deprived bowels.

Originally it was thought our cells were outnumbered 10 to one.
"That's been refined much closer to one-to-one, so the current
estimate is you're about 43% human if you're counting up all the
cells," he says.

But genetically we're even more outgunned.

The human genome - the full set of genetic instructions for a human
being - is made up of 20,000 instructions called genes.

But add all the genes in our microbiome together and the figure comes
out between two and 20 million microbial genes.

Prof Sarkis Mazmanian, a microbiologist from Caltech, argues: "We
don't have just one genome, the genes of our microbiome present
essentially a second genome which augment the activity of our own.

"What makes us human is, in my opinion, the combination of our own
DNA, plus the DNA of our gut microbes."
"https://www.bbc.com/news/health-43674270"

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