Life on the energy limit

How can microorganisms survive when there is hardly any energy or nutrients available? This question is the subject of a new review article by researchers at Friedrich Schiller University Jena and Linnaeus University in Sweden, which has now been published in the journal Nature Microbiology. In it, Prof. Dr Kirsten Küsel and Prof. Dr Mark Dopson propose the concept of »microbial frugality« – a new framework that explains how microorganisms survive under the extremely energy-poor conditions of groundwater whilst still maintaining key material cycles.

Beneath our feet lies one of the Earth’s largest and, at the same time, least researched habitats. Vast microbial communities thrive in aquifers, rock pores and deep crevices – without sunlight, with only a few nutrients and operating at the very limits of what is energetically possible. In their joint review article, Prof. Dr Kirsten Küsel of Friedrich Schiller University Jena, spokesperson for the Cluster of Excellence »Balance of the Microverse«, and Prof. Dr Mark Dopson from Linnaeus University in their joint review article.

Microbial frugality as a new framework concept

At the heart of the paper lies the concept of »microbial frugality«. It describes evolutionarily developed traits that enable microorganisms to minimise their energy consumption, utilise available resources efficiently and survive in the long term even under chronic energy deprivation.

For the review, they analysed numerous international studies on groundwater ecosystems and synthesised their findings within a shared conceptual framework. This revealed that microorganisms worldwide have developed similar adaptations to cope with chronic energy and nutrient shortages. 
Life at the energy limit

Many groundwater microorganisms grow extremely slowly, utilise different energy sources flexibly, or rely on close metabolic partnerships with other microorganisms. At the same time, they remain in an energy-saving standby state, which allows them to react immediately to short-term nutrient inputs or to mobilise stored energy reserves. Together, these characteristics enable them to live permanently under conditions that were long considered virtually uninhabitable.

»Groundwater microorganisms live permanently at the energy limit«, explains Prof. Küsel. »Our analysis shows that their evolutionary adaptations enable them to remain active over very long periods, even under chronic energy deprivation. We describe this principle as microbial frugality.«

Implications for climate and water resources

The significance of these findings extends far beyond microbiology. Groundwater is the Earth’s largest reservoir of liquid fresh water and supplies billions of people worldwide with drinking water. At the same time, the microorganisms living there influence key material cycles: they sequester carbon, degrade methane and regulate the transformation of nitrogen, sulphur and iron compounds. In doing so, they make a significant contribution to the chemical stability of groundwater ecosystems and to the regulation of climate-relevant gases.

The authors regard their framework as an important basis for gaining a better understanding in future of the role of groundwater in global material cycles, in water quality and within the climate system.

»These microorganisms are among the most hidden, yet at the same time most important, players on Earth,« says Küsel. »Anyone who wants to understand and protect the future of our groundwater resources must also take into account the communities that exist deep underground under conditions of chronic energy deprivation.«