Key points:
- Aerobic methane-oxidizing bacteria (MOB) remain active even in oxygen-free water.
- MOB contain specific genes that are used for methane-based fermentation and allow the bacteria to act as a sink for methane carbon.
- The importance of MOB for methane degradation is expected to grow as climate change affects conditions in anoxic lakes.
Methane is a greenhouse gas that is frequently produced in the sea and in fresh water where microorganisms prevent its release into the atmosphere. These microorganisms, known as methanotrophs, use methane to grow and generate. Their abilities and impact on the climate are detailed in a new study published in Nature Communications.
Researchers examined aerobic methane-oxidizing bacteria (MOB) from Lake Zug – a 200-meter-deep lake that is permanently oxygen-free from a depth of 120 meters. They added methane molecules that were labeled with heavy carbon atoms to the natural lake water samples containing the MOB. Next, they followed the path of the heavy carbon in individual cells using NanoSIMS and observed how active bacteria converted the methane into carbon dioxide. The team also used metagenomics and metatranscriptomics to identify which metabolic pathways the bacteria used.
Their results demonstrated that aerobic MOB remain active even in oxygen-free water. A particular group of MOB, recognizable by their rod-shaped cells, were equally active with and without oxygen.
The metabolic analysis revealed that MOB contain genes that are used for a special type of methane-based fermentation when oxygen becomes scarce. This discovery was the first time the process was characterized outside of the laboratory. As a result of this process, MOB release substances that other bacteria use for growth, meaning that the carbon contained in methane is retained in the lake for longer periods of time.
“Methane oxidation by microorganisms is the only biological sink for methane,” explained study author Sina Schorn of the Max Planck Institute. “Given the current and predicted increase in anoxic conditions in temperate lakes, the importance of MOB for methane degradation in lakes is expected to grow. Our results suggest that MOB will make a significant contribution to greenhouse gas mitigation and carbon storage in the future.”