Prof. Dr. Dieter Spiteller, head of the new Department of Chemical Ecology at the University of Konstanz, is investigating how organisms interact with each other by way of chemical signals, antibiotics and toxins. Spiteller and his team of researchers are using leafcutter ants endemic to South and Central America as one of several research objects.
Leafcutter ants are known for their habit of cultivating the fungus Leucoagaricus gongylophorus in the chambers of their nests. The ants cultivate the fungus by feeding it with freshly cut leaves. As part of this symbiotic relationship, L. gongylophorus is one of the ants’ major food sources. A symbiotic relationship implies that neither of the partners can stay alive without the other. Therefore, the ants look after the fungus with extreme care, keeping it free from pests and moulds. Pathogenic fungi such as the necrotrophic parasite Escovopsis threatens the ants’ food source (L. gongylophorus) and is therefore a permanent danger to them.
In order to fight off parasitic pathogenic fungi, the ants have developed specific defence strategies and they also live in a symbiotic relationship with the Actinomycetes bacteria that grow on them and secrete antibiotics. In cooperation with colleagues from Kaiserslautern and Panama, Dieter Spiteller’s group is looking into which antibiotics are excreted by the bacteria.
Around ten years after Dr. Currie and his team discovered that leafcutter ants live in symbiosis with Actinomycetes bacteria, Dieter Spiteller’s group succeeded in isolating antibiotics from Streptomycetes bacteria, which also live in a symbiotic relationship with leafcutter ants. These antiobiotics strongly inhibit the pathogenic fungus Escovopsis weberi. Spiteller and his group used a broad range of analytical methods, including high-resolution mass spectrometry, to investigate the compound and found that the antibiotic was a candicidin macrolide. These compounds belong to the complex group of polyene macrolide antibiotics, to which nystatin also belongs. Nystatin is used for the effective treatment of Candida infections. As candicidin macrolides are highly effective in combating Candida albicans, the first candicidin macrolides were isolated from Streptomyces griseus as early as 1953. It appears that leafcutter ants as well as human beings use bacterial compounds for warding off infectious diseases.
Ilka Schoenian, a doctoral student in Dieter Spiteller’s group, has developed a method that enables the rapid identification of a large number of antibiotics – antimycins, valinomycins and actinomycins – produced by the symbiotic partners of leafcutter ants. Using MALDI imaging, the researchers were also for the first time ever able to directly observe the distribution of valinomycin on the body of leafcutter ants. This clearly shows that leafcutter ants are ecologically important insects.
“The symbiotic relationships between bacteria and higher organisms (e.g., leafcutter ants) might prove to be a promising source for new drugs for the treatment of infectious diseases because insects have established symbiotic relationships with bacteria that are able to produce potent compounds that have huge potential for application in medicine,” said Prof. Spiteller highlighting his plans to specifically focus on bacteria that live in symbiotic partnerships with leafcutter ants and that have not so far been a central object of research. Some secondary metabolites are only produced under specific conditions, which it is why it does not always make sense to investigate the interacting partners in isolation from each other.
Interesting interactions can also be found between plants and microorganisms. Working with Beate Völksch from the Department of Phytopathology at the University of Jena, Spiteller has investigated how epiphytes, i.e. microorganisms that grow on leaf surfaces, are able to protect their hosts against attack by phytopathogens. For example, the bacterium Pseudomonas syringae pv. syringae 22d/93 (Pss22d), which grows epiphytically on soybeans, produces the rare amino acid 3-methylarginine which is highly active against the closely related soybean pathogen Pseudomonas syringae pv. glycinea. “3-methylarginine is very effective; nanomolar concentrations are sufficient to kill Pseudomonas syringae pv. glycinea, which is the cause of one of the most common bacterial diseases (bacterial blight) of soybeans,” explained Prof. Spiteller. In addition to identifying 3-methylarginine, the researchers have also shown that the biosynthesis of 3-methylarginine only involves three genes. This is relatively energy efficient compared to the energy required for the synthesis of complex antibiotics, which involves a much larger number of different genes.“Derivatives of 3-methylarginine are also of pharmacological interest as they have an inhibitory effect on the production of nitrogen monoxide,” explains Dieter Spiteller. The researchers will continue to look even more closely at the underlying mechanism of action.
Dieter Spiteller plans to extend his research on the symbiotic relationships between microorganisms and other organisms to aquatic organisms of Lake Constance. So far, little is known about such symbioses. Investigations relating to the lake’s chemical ecology will be carried out in close cooperation with Spitellers’ colleagues, Prof. Bernhard Schink and Prof. Peter Kroth from the University of Konstanz.Spiteller hopes that his team’s work will lead to new insights into the chemistry of biological systems. The researchers are focusing on the identification of secondary metabolites using specific bioassays as well as on the investigation of the biosynthesis, regulation and ecological function of bacterial secondary metabolites. “Newly identified natural compounds and their biosynthesis gene cluster not only provide a profound understanding of the chemistry of microbial interactions with their environment, they might also be of great benefit for medical-pharmaceutical and biotechnological applications,” said Spiteller summarising the focus of his research.
Dieter Spiteller has been professor for chemical ecology at the University of Konstanz since April 2011. Prior to this, Spiteller was head of the Microbial Chemical Ecology Emmy-Noether research group at the Max Planck Institute for Chemical Ecology in Jena. He did his doctorate on the characterisation of N-acetyl glutamine conjugates of Lepidoptera larvae at the Max Planck Institute for Chemical Ecology under the supervision of Prof. Dr. Wilhelm Boland.
Prof. Dr. Dieter SpitellerUniversity of KonstanzFaculty of BiologyTel.: +49 (0) 7531/ 88 3931E-mail: dieter.spiteller(at)uni-konstanz.de