Lichtgedanken 03

Rubrik 30 We humans are colonized by many dif- ferent microorganisms. Not only have we become used to one another, we are also interdependent, as evidenced by our intestinal flora, for example (see p. 18). Although a few bacteria or fungi frequently cause serious ill- nesses, we could not survive without most microorganisms. The same is true of other organisms that coexist with microbes. For example, microor- ganisms in the root environment in the soil have a symbiotic relationship with plants and help them to absorb nutrients. And insects, too, have their own very individual intestinal flora, on which they depend. Termites create gardens in their mounds to cultivate fungi »In the gut and the fungus gardens of termite species that cultivate fungi, we find what are called actinobacteria. They play an essential role for the in- sect community,« says Beemelmanns. The chemist leads a junior research group at the HKI, which is studying the interrelationships between micro- bes and their host at the chemical level. In 2015 and 2016, together with an in- terdisciplinary research group, Bee- melmanns undertook expeditions to South Africa, where fungus-cultiva- ting termites live. With her colleagues, she took samples from termite mounds: »We had to dig deep in order to reach the termites’ fungus garden,« she adds. »Similar to our cultivation of grain, ter- mites cultivate a fungus of the genus Termitomyces in order to feed on it,« explains Beemelmanns. Many different factors have to be in equilibrium for such a highly complex and fragile so- ciety as that of the termites to remain intact. In addition to abiotic factors such as the composition of the soil, it is the interac- tion between the organismic partners that is of decisive importance. Only if the fungus used as a source of nutriti- on and the termites’ supporting micro- bes are in a balanced relationship can such a complex system survive. Bioac- tive substances, as they are known, are particularly important in this process, because they serve the organisms con- cerned as signal and communication substances. In this way, the microorganisms regulate their interactions and keep the system in equilibrium. In a similar way to human beings with their complex microbiomes, insect communities form a kind of su- perorganism. However, these ecological systems are also vulnerable and are oc- casionally infested by pests or succumb to infections. For example, parasitic fungi can overrun the vital nutritional fungus and cause the entire colony to collapse. Christine Beemelmanns’s junior re- search group is working on these microbe-host relationships. She believes that they hold great potential for fin- ding new natural products that could be used in fighting human infections, for example. Instead of randomly ex- tracting substances from samples, Bee- melmanns’s team first studies bioactive natural products within the organismic In a termite colony, there is—quite literally—the right chemistry. Busy termites cultivate a fungus in large fun- gus gardens and feed on them. They are assisted by bacteria in protecting this valuable source of nutrients. These live in the termites’ gut and in their garden, and produce natural products that prevent hostile fungi from infesting the termite mound. Christine Beemelmanns, with her team at the Leibniz Institute for Natural Product Research and Infection Biology – Hans Knöll Institute (HKI), is investigating the relationship between host and bacteria, and in the process she is discovering new natural products. Termites have »green fingers« BY MONIKA WEISS Mound of a Macrotermes colony in South Africa. F E AT U R E