Purifying water with biotech: the role of funghi in aquatic ecosystems

By Elcke Vels

Nitrogen, mainly in the form of inorganic nitrite and nitrate, is one of the major material pollutants in freshwaters and human wastewater. Researchers from the Chinese Ministry of Natural Resources in Xiamen and Leibniz Institute of Freshwater Ecology and Inland Fisheries (IGB) have identified a natural fungus-bacteria combination that metabolizes nitrate particularly efficiently and consistently. This could be crucial for the further development of biotechnology in water treatment and is further evidence of the important role of fungi in aquatic ecosystems, says The Leibniz Association in a (German) press release.

Biological nitrogen removal is an important biochemical process. In this process, microorganisms convert two of the most important nitrogen compounds, nitrate and nitrite, into gaseous nitrogen. This occurs naturally in waterbodies through metabolic processes of the organisms living there and is referred to as self-purification. This principle is also used in water treatment. To date, various bacteria and fungi have been identified in pure culture that can break down nitrogen with and without oxygen. For water treatment, nitrogen degradation in the presence of oxygen is particularly relevant, as it is more cost-effective and can also be implemented on a large scale.

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Fermentation of foods and beverages

Isolating individual strains of bacteria or fungi is time-consuming and expensive. Combinations of the two, known as microbial consortia, are considered a promising alternative to pure strains, but are still little researched in the field of denitrification in the presence of oxygen. The researchers took this as an opportunity to investigate this potential, since microbial consortia have long been used, for example, in the fermentation of foods and beverages. Fungi in particular have the advantage of being very robust to environmental stressors such as acidic pH and high temperatures.

Almost complete nitrate removal possible

The research team identified a natural bacteria-fungi consortium from mariculture that removes nitrate from water very efficiently and consistently. In the presence of oxygen, nitrate removal is up to 100 percent and denitrification efficiency is 44 percent. Denitrification efficiency indicates how well microorganisms are able to convert the nitrogen bound in nitrate into molecular nitrogen (N₂) and nitrogen oxides.

High-throughput sequencing was used to identify the bacterial and fungal genera involved in this process. A subsequent network analysis showed which species interact positively with each other and are therefore particularly suitable for combination.

“We have succeeded in identifying denitrifying bacterial-fungal groups that have the potential to remove nitrate particularly well from water. This is an important step in putting together microbial consortia for optimal water treatment,” explains IGB researcher Professor Hans-Peter Grossart, co-author of the study.

Since the search for suitable microbial communities of bacteria and fungi is still a very young field of research, there are no practical applications yet. However, the authors are certain that these will significantly shape biotechnology in wastewater treatment in the future.