Temporal Microbiome Dynamics: From Circadian Rhythms to Probiotic Evolution

Microbial life is all around us and inside us in an unseen vast and varied ecosystem. For the past several decades, the microbiome field has attempted to characterize this microscopic web of life using next generation sequencing technology. It turns out that the number of host organism cells is generally outnumbered by the number of microbial cells that live on and within them. Moreover, these microbes collectively have two orders of magnitude more genes than their host organism. While the host organism’s genome stays constant during its life, the microbial community and its associated genes change much more frequently. Since microbial lifespans are sometimes measured in minutes, selective pressures in the host micro-environments can rapidly affect the evolution and gene content of the microorganisms present. Over the course of a lifetime, the host winds up with a unique set of microbes selected to fit their unique individual environment, from immune system quirks to specialized diets to biological rhythms. However, despite biological rhythms having always played a role in host behavior and survival, the impact of time on health has been a widely neglected realm until recently. The basic argument of this thesis is that time is an underappreciated but critical variable that impacts both experimental study design as well as host health