Science of a Superorganism
BE
INSPIRATION │ KNOWLEDGE
How do genes and
symbionts affect the
formation of new
species?
Seth R. Bordenstein is an American professor of biology at Vanderbilt University, Nashville, TN http://bordensteinlab.vanderbilt.edu. He is most well known for his work on symbiosis and
speciation and his development of citizen science programs including Discover the Microbes Within! The Wolbachia Project http://discover.mbl.edu. He holds two appointments in the
Department of Biological Sciences and Department of Pathology, Microbiology, and Immunology at Vanderbilt; and he has a joint appointment with the Marine Biological Laboratory, Woods
Hole, MA in the Bay Paul Center. You can follow Dr. Bordenstein on Twitter - @Symbioticism or visit his blog at - http://symbionticism.blogspot.com
Mouth Bacteria. Credit Robert Brucker
E pluribus unum is a good motto for the human body. Translated from latin, this phrase
means Out of many, one . If you re like most people, when you look in the mirror, you see a
single organism ‒ yourself - one individual out of the billions of humans that inhabit the
planet. But if you re a microbiologist like myself, I see one human plus the trillions of
microorganisms that live in symbiosis with you.
In fact, I see as many microorganisms inside your mouth, as there are people on the planet.
Is this delusional? Science fiction? Hardly. What I am talking about are the trillions of
microscopic bacteria that live in or on your body, all the time. You need these bacteria for
untold reasons, including digesting food and mounting an immune response against
infections that should not be in your body. The principle motivation for why I choose to study
this topic is because I am fascinated by the facts and unknowns about the following
observation ‒ each one of us is not just a single organism, but rather one superorganism
composed of bacteria, viruses, and our own cells.
In the last decade, biologists have discovered that there are thousands of different bacterial species inside or on us. Among these bacteria are just a few
dozen species that catastrophically make us sick. So while human nature has conditioned us to have germ phobias, the truth is that we need our
microbial associates. They are not only our friends, but they are essentially us. A human cannot exist without their bacterial passengers, but the bacteria
will do just fine without you. The laws of nature are the same everywhere. Beyond humans, other animals owe their existence to the microscopic
symbionts within them. These microorganisms, in fact, populate the Earth in every imaginable and inhospitable place ‒ from polar ice caps to deep sea
hydrothermal vents, from plant roots to boiling springs, from indoor environments to the sky. In fact, if you were to sum up the weight of all bacteria on
Earth, they would outweigh humans roughly 5000 to 1. That is, for every one pound of human weight on the planet, there are 5000 pounds of bacterial
weight. Furthermore, for every one cell in the human body, there are 10 times as many cells of symbiotic bacteria. For every one gene in your genome,
there are 100 times as many genes from the collective genome of the bacterial community in you. Despite the inferior size of bacteria, it is actually the
human cell and genome that are inferior in number to those of our symbiotic bacteria.
BE
Science of a Superorganism
INSPIRATION │ KNOWLEDGE
If you strain to understand what you are reading, consider this. The bacteria on
your skin mix with your sweat to affect how attractive you are to mosquitoes
(Verhust et al. 2011). The bacteria in your gut may enhance whether you are
obese or lean (Turnbaugh and Gordon 2009). The bacteria on women s hands
are more diverse than the bacteria on men s hands (Flerer et al. 2008). We are
now in a historic age. How biology looks at the human body has fundamentally
changed because of these and many other discoveries. We have perhaps found
this perspective just in time as well. With the rise of antibiotic resistance that
depletes our arsenal to kill bad infections, the knowledge of the gifts that good
The Laws of Nature are the same everywhere!
microbes bestow to our body creates new opportunities to control which
Microorganisms populate the Earth in every
microbes go in us. For instance, a probiotic pill of good bacteria has the
imaginable and inhospitable place - from
potential to restore the balance of our health when bad microbes are a threat.
plant roots to boiling springs.
After billions of years of biological evolution, microbial life has earned a legacy
that cannot be denied. All large fauna and flora that we observe without the aid
of a microscope owe their well-being to the microscopic life that inhabit them.
These microbes are not only prevalent, but also specific to each species that
they inhabit. For instance, in humans and our close relatives, the human
bacterial community is slightly different from the chimpanzee bacterial
community, which is slightly different from the gorilla bacterial community and
so on (Ochman et al. 2010). What this finding implies is that the bacteria
perform specific functions to each species that they inhabit, just as the genes
on chromosomes perform specific functions. Often, the genes interact with the
bacterial symbionts, as in the case of immunity genes.
One of the themes that motivate my science is the relative importance of genes
vs. bacterial symbionts in the evolution of life (Bordenstein et al, 2001; Brucker
and Bordenstein 2012). From a biodiversity perspective, I seek answers to how
do genes and symbionts affect the formation of new species ‒ the process by
which one species splits into two and ultimately to form the 1.8 million species
on Earth? It is important to note in conclusion that answering this question,
among others, happens with the energy, passion, and curiosity of young
scientists that devote their life to science literacy, education, and
professionalism. Alongside doctoral student Robert Brucker (follow on twitter
@liveinsymbiosis), we are now discovering new ways in which speciation is
dependent on interactions between bacteria and genes.
ARTICLE CITATIONS
✦Bordenstein SR, O Hara FP, and JH Werren (2001) Wolbachia-induced incompatibility
precedes other hybrid incompatibilities in Nasonia. Nature 409(6821):707-710. ✦Brucker
RM and SR Bordenstein (2012) The roles of host evolutionary relationships (genus: Nasonia)
and development in structuring microbial communities. Evolution 66(2): 349-362. ✦Flerer,
N, Hamady M, Lauber CL and R Knight (2008) The influence of sex, handedness, and
washing on the diversity of hand surface bacteria. Proceedings of the National Academy of
Science 105(46):17994-17999. ✦Ochman H, Worobey M, Kuo C-H, Ndjango J-BN, Peeters M,
et al. (2010) Evolutionary relationships of wild hominids recapitulated by gut microbial
communities. PLoS Biol 8(11): e1000546. doi:10.1371/journal.pbio.1000546. ✦Turnbaugh,
PJ and JI Gordon (2009) The core gut microbiome, energy balance, and obesity. Journal of
Physiology 587:4153-4158. ✦Verhulst NO, Qiu YT, Beijleveld H, Maliepaard C, Knights D, et
al. (2011) Composition of Human Skin Microbiota Affects Attractiveness to Malaria
Mosquitoes. PLoS ONE 6(12): e28991. doi:10.1371/journal.pone.0028991
If you were to sum up the weight of all bacteria
on Earth, they would outweigh humans
roughly 5000 to 1.