Novel microorganisms play major role in one of nature's most important processes

The scientists believe their findings about a type of microorganism found in soil could lead to a reassessment of current thinking on nitrogen cycling – a process which is vital for all plants and animals.

The studies published in Nature today (August 17) could also yield new insights into the production of greenhouse gases and the pollution of groundwater, and could potentially provide new clues for more efficient and more cost-effective fertilisation processes for farmers.

The researchers from the University of Aberdeen; the University of Bergen, Norway; the Institute of Soil Ecology and the Institute of Geology and Mineralogy, both Germany, and Pennsylvania State University, America studied a group of microbes called Crenarchaea whose existence in soil and seawater was only discovered around 14 years ago.

By carrying out genetic analysis of soil samples, the team discovered evidence that Crenarchaea are responsible for most of the world’s oxidation of ammonia in soil.

The finding turns current thinking on its head – up until now it has been thought that ammonia oxidation was restricted to another type of microbe: bacteria.

Ammonia is produced naturally in the soil by bacteria decomposing dead plants and animals and animal waste.

Ammonia is then converted to nitrite, through a process called ammonia oxidation, and subsequently to nitrate. This process is called nitrification and is a key part of the nitrogen cycle, which sustains living things on Earth.

The ammonia oxidation process – the first step of nitrification – also results in the production of nitrous oxide which is a greenhouse gas.

Nitrates from ammonia oxidation also leach into the groundwater.

In this new study the researchers have discovered that ammonia oxidising Crenarchaea are more abundant than bacteria and, potentially, more important in oxidising ammonia.

Professor Jim Prosser and Post Doctoral Research Fellow Dr Graeme Nicol were the University of Aberdeen collaborators on the research. Professor Prosser said: “The results published in Nature indicate that bacteria are only minor players in ammonia oxidation in soil and that most oxidation is performed by Crenarchaea.

“Our findings show that this group of microorganisms, which was unknown just over a decade ago, may be responsible globally for most of the oxidation of ammonia in soil.”

Ammonia-based fertilisers are added to the soil by farmers to enhance crop production, as nitrogen is a major plant nutrient requirement. However, nitrate, produced by nitrifying microorganisms, is easily washed out of soil, resulting in significant economic losses to the farmer.

Professor Prosser added: “If Crenarchaea are the world’s most efficient ammonia oxidizing microorganism we should be targeting that group of microbes rather than bacteria.

“If we are able to inhibit the workings of this group of microorganisms it could cut down on greenhouse gas emissions, cut down on water pollution and possibly lead to the development of more effective fertilisers for farmers.”

Source: University of Aberdeen