(With thanks to Alfonso Jiménez-Sánchez for the article "ADN libre" in his blog "La Ciencia también es Cultura" and to Hans
Bergmans, whose comments and corrections I gratefully incorporated)
Many different bacteria
(microorganisms) inhabit all those parts of the human body that are in frequent
contact with the outside world. Under certain health conditions some bacteria (so-called
pathogens) can cause illnesses, but most of the time they live with us in
harmony, providing functions that are vital for our survival (like food
digestion and breaking down poisons).
Studies have estimated that there
are about 10 bacteria for every human cell in our body. But how many cells do
we have? This is difficult to determine. If our body would contain 10 trillion
cells (10 x 1012) the weight of 100 trillion bacteria (average
weight = 5 x 10-12 gram) would be 500 gram or half a kilogram. There
are also estimates that the total weight of bacteria in and on the body of an
adult person amounts to 1 to 3 kg.
A bacterium from our gut, like Escherichia coli, can
have many different sizes and shapes. These bacteria can weigh between 0.5 to
10 x 10-12 gram depending on their growth condition.
Previously a few hundred
bacterial species were isolated from the human body. In 2012, researchers from
the "Human Microbiome Project" published reports describing 10,000
species in our body, based on analysis
of their DNA. The vast majority of
these species have not yet been cultured. Taken together their DNA codes for some 8 million
unique proteins, that is 360 times the number of proteins coded by our own DNA.
Many of those proteins help us to digest and absorb the food we are eating.
But, in addition, the bacteria produce compounds like vitamins that our genes
cannot produce (genes are "instruction manuals" present in every
single cell of our body; they direct the building of proteins, the
"machines" that make our body function).
When we eat our food consisting
of plant and animal tissue, we eat cells that contain DNA. This DNA is broken
down into small fragments. According to a recent study (Spisák and others, July
2013) some of these fragments can contain genes and can end up in our blood
stream (see also Alfonso Jiménez Sánchez, who pointed out this article to me in
his article "ADN libre").
The article of Spisák in PLOS ONE (July, 2013)
How should we read such a
difficult, technical article? Either, as a human being with deep-seated fears
for the uncertainties life brings us, or, as a skeptic who accepts the
uncertainties of life, but does not immediately accept the remarkable results
in this article?
The first category is well
supplied by, for instance, anti-GMO web sites (links 1 and 2) like ISIS
(Institute of Science In Society), in which "the hazards of GM and other
unknown nucleic acids introduced into the human food chain by GMOs" are
emphasized. The second category is supplied, for instance, by a pro-GMO blog
"The skeptical Raptor", in which it is pointed out that this mystery
has not yet been confirmed by an independent study and that, if it is confirmed,
it must always have been so. (See also "The Conversation".)
There is a strange tendency amongst critics of
genetic engineering, to assume that the DNA that has been added or changed in a
transgenic organism (GMO) has a special status amongst the vastly larger amount
of DNA that is naturally present in the organism. The transgenes do not differ
in physical and chemical properties from the DNA of other organisms. It is
likely that fragments of DNA of any organism that we eat will find its way into
our body. In fact, during millions of years of evolution we have developed as
organisms that, for our maintenance and multiplication, have to rely on eating
other organisms, and thus on eating their DNA. Vast amounts of DNA have entered
our system, but there has never been any evidence that this DNA is doing
something wrong. No form of cancer has been identified that results from the
plant or animal DNA we are eating. Why would the transgenic DNA in a trangenic
organism then behave differently?
This last question will
certainly not take away the anxiety in people who do not like to live with uncertainties.
