Gaia and her microbiome

Abstract

The Gaia hypothesis, proposed 50 years ago, posits that the Earth's biosphere, atmosphere, hydrosphere and lithosphere interact as a cybernetic system, maintaining the long-term habitability of the planet. The resulting chemical composition of the atmosphere, oceans and crust is unique as compared to the other planets of our solar system, and due to the presence of life. Together these components comprise the biosphere, the life support system of the planet, with most of the essential processes carried out by microbes. Over a half of the elements in the periodic table are now known to have some biological role with many having complex biogeochemical cycles. The global microbiome inhabits a wide range of environments including deep into the Earth's crust, with a population of ∼10³⁰ cells and more than a trillion species. Deep sequencing projects have revealed hitherto unknown phyla and 'microbial dark matter'. The discoveries of conductive pili and cable bacteria have demonstrated that microbes transfer electrons to and from external sources, sometimes over significant distances, while research on quorum sensing and the plethora of microbial volatile organic substances have provided new insights into how microbes communicate. These advances in microbiology have expanded our understanding how Gaia could actually work.

Keywords: Gaia theory; biogeochemical cycling; climate change; extracellular electron transfer; microbial dark matter.