Hibernating bacteria can invade hospitals and survive outer space—but their energy budget reveals a weakness

Bacterial spores, often found in soil, possess the remarkable ability to withstand extreme conditions such as boiling, desiccation, radiation, and even the vacuum of space. NASA once demonstrated this resilience by sending Bacillus spores to orbit for nearly six years, with the spores shielded from sunlight returning to life upon their return to Earth.

These spores, even after billions of years of evolution, serve as a survival mechanism for bacteria, allowing them to endure harsh environments before resuming their metabolic activities once conditions become favorable.

However, when these bacteria are provided with optimal growth conditions in a laboratory setting, they eventually lose the ability to form spores. This paradox, where a trait so vital for survival can disappear in just a few thousand generations, has puzzled microbiologists for decades. The answer, as researchers propose, lies in the energy costs associated with forming and activating these spores.

In their research published in the Proceedings of the National Academy of Sciences, Jay Lennon, William Shoemaker, and colleagues calculated the energy expenditure involved in creating and activating a bacterial spore and found that this energy cost is significant enough to drive evolutionary changes, such as the loss of spore-making genes when they are not needed.

The energy accounting of spore formation shows that it is one of the most costly processes a bacterium undergoes, requiring approximately 10 billion ATP molecules—one of the most expensive endeavors for a bacterium. In comparison, building a flagellum and swimming to find food costs a fraction of this energy. Moreover, much of the ATP expenditure in spore formation is an opportunity cost, as it involves using resources that could otherwise be allocated to producing new cells.

A spore, therefore, not only consumes energy but also forgoes the opportunity to reproduce while other bacteria in its vicinity are actively dividing.

Interestingly, dormant spores contain little readily available fuel, needing approximately five orders of magnitude less ATP to activate compared to what they expend during their formation. Instead, they carry raw materials such as proteins and small amino acids, which can be broken down into essential building blocks for reactivation.

This pantry-like storage allows the spore to begin the germination process under adverse conditions. The cost of building a spore is heavily borne by the mother cell, which provides materials through a specialized channel and then dissolves itself to release the spore. Despite this investment, the spore still requires external food sources to complete its awakening.

The process of awakening consists of two stages: initial rehydration and shedding of the protective armor, followed by a period of rebuilding essential cellular components, which can take hours to complete.