E pluribus unum

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.

Indeed, our bodies are a complicated society of microbes and human cells that get along to make one superorganism. Despite the bacteria's inferior size, they

• outnumber human cells by 10:1 and 
• the bacterial genes outnumber the genes on your chromosomes by at least 100:1. 

We are more bacterial than human in terms of cell number and gene number. Most of these bacteria live in your gut.

An Undeniable Legacy, Billions of Years in the Making: After billions of years of biological evolution, microbial life has earned a legacy that cannot be denied. All animals and plants that we observe without the aid of a microscope owe their well-being to the microscopic life that live inside 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 assemblage is slightly different from the chimpanzee bacterial community, which is slightly different from the gorilla bacterial community and so on (Ochman et al. 2010).  We see the same pattern in insect species that my lab studies (Brucker and Bordenstein 2012). In fact, we see the pattern even when we control their diet, thus specifying that animal species select for and diverge in parallel with the numbers and types of microbial symbionts inside them (Gut Microbes May Drive Evolution, Scientific American). What these findings imply is that each animal's microbial assemblage performs specific functions to that animal, just as the genes on chromosomes perform specific functions.  Often, the genes interact with the bacterial symbionts, as in the case of our immunity genes. Thus, humans and other animals can not live without their microbial symbionts. They can not be ignored, for they are as much us as our genes are.

Three Simple Messages: The central theme that motivates this blog and the science and outreach in my lab is the relative importance of genes vs. bacterial symbionts in the evolution of life (Bordenstein et al, 2001).

1. 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. I will discuss more of this topic soon. 
2. From a genetic perspective, I seek answers to how often and why genes are swapped between interacting organisms, such as between bacterial coinfections, or between a host and its symbiont - a process referred to as horizontal gene transfer
3. From a mechanism perspective, I seek answers as to how animal genes regulate and coordinate with their bacterial symbionts to shape the laws of their complex, interacting society.

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.

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