Deep below the surface of the South Pacific Ocean, buried beneath 70 metres of seafloor sediment, there are microbes that may be about 75 million years old. These organisms are among the oldest known life forms on the planet, yet exactly how they manage to maintain their near-immortality has remained a mystery.
James Bradley, a geobiologist at the University of Southern California, and his colleagues think they have solved the puzzle: to stay alive, the microbes stay mostly dead. They burn next to no energy.
Researchers already knew that the microbes must have extremely low metabolisms, but it was unclear exactly how much food they have to burn to keep on going. 鈥淲e haven鈥檛 been able to determine in a quantitative way whether they鈥檝e been growing since they鈥檝e been buried, or whether or not they鈥檙e lying dormant,鈥� Bradley says.
Advertisement
Extreme dieting
By producing a model that took into account factors such as the density of microbes in the sediment and the density of food in that sediment, Bradley and his team calculated the energy requirement of the microbes. 鈥淸It] is equivalent to the energy that is released by burning just two per cent of their carbon biomass per year,鈥� he says. In absolute terms that鈥檚 0.00000000001 (10-11) joules per year 鈥� Bradley says a human uses one hundred quintillion (1020) times more energy per year.
鈥淭his is like a party of 100 people, and you only ordered one pizza,鈥� says Karen Lloyd, a microbiologist at the University of Tennessee, Knoxville who was not involved in the new work.
Calculating exactly what it takes for these microbes eke out a living illuminates how life can hang on even in the most inhospitable of environments. And that, Bradley thinks, could one day help in the search for life on distant worlds, especially those that may at first glance appear to be inhospitable to life. 鈥淚f we鈥檙e looking for life on Mars or Europa 鈥� there are very harsh surface conditions of these planetary bodies 鈥� the most likely place we鈥檙e going to find life in these environments is in the subsurface.鈥�
Geobiology
