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Researchers Estimate Maximum Growth Rate for Life on Earth

Research presented at the Astrobiology Science Conference in Arizona has challenged assumptions about how microbes behave at high temperatures.

It’s common knowledge that microbes grow at a faster rate at higher temperatures, such as the everyday example of milk going “off” when it’s left out of the fridge. However, Dr Ross Corkrey’s laboratory at The University of Tasmania last year discovered that the maximum rate of microbial growth plummets dramatically once temperatures reached somewhere above 40°C. This distribution of growth rates was termed the Biokinetic Spectrum for Temperature (BKST).

Building on this work, the team has now quantified the data and provided an estimate on the maximum growth rate for life on Earth. “We now find that the predicted maximum growth rate occurs at 45.8°C, with an estimated minimum generation time of 5.16 minutes. This means that the shortest possible time in which a cell can divide to make two daughter cells is a little more than 5 minutes,” Corkrey said. “We are now considering how this limit may influence ecological processes that vary by temperature, including, perhaps, those of marine plankton.”

To arrive at the numbers, the team collated more than 10,000 measurements of growth rates representing 1627 microbe strains. “We mathematically modelled them to obtain the predicted maximum rate of growth versus temperature for any life on Earth,” Corkrey said.

The vast bulk of the BKST describes growth rates for most of life, but there are still deviations at temperatures below 0°C and above 100°C. “This could mean that the growth rate drops due to some unknown property, perhaps such as changing bulk properties of water, like diffusion of molecules at low temperatures, and at high temperatures the deviation may be due to an increasing degree of denaturation and degradation of biomolecules,” Corkrey said.

“Alternatively, it could mean that there are organisms that grow slowly at these temperatures that are undiscovered.”

“It is notoriously difficult to grow organisms at low temperatures, so it would not be surprising if we have not found them. These would be organisms that still grow slowly compared to more familiar forms of life, but much faster than those we so far know about. Perhaps they would be found in glacial ice. Similarly, it is possible that there may be relatively fast-growing organisms growing in hydrothermal vents at the bottom of the sea.”

The team is now exploring how the growth limits of life depend on other conditions such as acidity and salt concentration.