Tar-eating bacterial duo may transform toxic compounds into new usable materials

Environment and sustainability 15. may 2017 2 min Professor Søren Molin, Associate Professor Sünje Johanna Pamp Written by Morten Busch

Danish researchers have sequenced and analyzed the genome of a bacterium that can feed off coal tar. It lives in symbiosis with another bacterium that can recycle its partner’s waste. Researchers hope that this sustainable bacterial duo can transform toxic substances into useful materials. Nevertheless, mapping the genome also led to an unpleasant surprise.

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Danish researchers have a new bacterium in their spotlight. Called Acinetobacter johnsonii C6, it was discovered in 1994 on the site of a gas works in Fredensborg, north of Copenhagen. It seemed to thrive in the toxic wood preservative creosote – a dark viscous fluid made from coal tar. Now researchers from the Technical University of Denmark have mapped the bacterium’s genome because they hope to use its special properties in other settings.

“This bacterium is not just fascinating biologically. We hope that we can use its unique abilities to break down materials such as aromatic hydrocarbons that are present in coal and oil as well as plastics and pesticides. The genomic data show that it contains the enzymes we hoped to find and additional ones we did not expect, so we hope we can use this bacterium to dispose of substances that are otherwise difficult to break down,” explains co-author Søren Molin from the Novo Nordisk Foundation Center for Biosustainability at the Technical University of Denmark.

Can thrive on almost anything

Nevertheless, this bacterium is especially interesting for a completely different reason. Acinetobacter johnsonii C6 can live in symbiosis with another bacterium, Pseudomonas putida, which is already being used to purify contaminated soil because it can convert styrene into biodegradable polyhydroxyalkanoates. This has enabled materials such as polystyrene foam to be recycled despite otherwise being categorized as not biodegradable.

“These two bacteria can coexist symbiotically – a metabolic dependence in which each one needs the other. We hope to use this dependence to establish a stable consortium of Acinetobacter johnsonii C6 to break down unusable or harmful substances and Pseudomonas putida to use its waste products further as the basis for producing new usable materials.”

The best way these two bacteria can coexist is in a biofilm – thin films of bacteria stuck together by a type of chemical glue. Biofilms are already known from deposits in nature such as on stones in a riverbed and in sewage treatment plants where they break down contaminants.

“The unique collaboration between these two bacteria integrated into a biofilm makes this very interesting and industrially relevant in addition to the individual biotechnological bacteria used today. These bacteria can thrive on almost anything. In contrast, Escherichia coli bacteria, for example, are much less robust and flexible because they cannot tolerate or use many chemicals,” explains one of the driving forces behind the project, Sünje Johanna Pamp from the National Food Institute of the Technical University of Denmark.

A multidrug-resistant surprise

Nevertheless, mapping the genome of Acinetobacter johnsonii C6 provided an unpleasant surprise. The researchers discovered several antibiotic resistance genes in this bacterium that enables it to survive several antibiotics such as chloramphenicol, trimethoprim and cefoxitin. This is especially important because bacteria often transfer antibiotic resistance genes between each other.

“We definitely do not want to create a new problem while solving another one. If we had started to use these bacteria to break down toxic substances on a large scale, we might have disseminated their antibiotic resistance genes. It is therefore fantastic that we can investigate the bacteria genomically so we can remove such problematic genes before working with them further,” explain Sünje Johanna Pamp and Søren Molin.

The spread of bacteria that resist most of the available antibiotics is a growing problem. Some Acinetobacter species are among the most resistant; this is why they are difficult to contain in hospitals and therefore can cause a broad spectrum of infections such as pneumonia and meningitis. The new knowledge may therefore also prove to be useful in this respect.

“These results illustrate well how the current boundaries between infectious diseases, cleaning up contaminated sites, biotechnology, and food production are extremely fluid. Similar microorganisms and mechanisms can be relevant in many situations. The new genome-based techniques enable research to be carried out in major interdisciplinary collaborations instead of previously, when scientific disciplines were completely separate.”

Researchers from the National Food Institute and the Novo Nordisk Foundation Center for Biosustainability of the Technical University of Denmark have published “Draft genome sequence of Acinetobacter johnsonii C6, an environmental isolate engaging in interspecific metabolic interactions” in Genome Announcements.

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