From hot and nutrient-poor deserts to alternating dry and wet intertidal zones, right through to the highest water pressure and permanent darkness in the deep sea: in the course of its development over millions of years, life has conquered even the most extreme places on earth. That termites can live off indigestible wood, plants can exist in deserts - seemingly without water and nutrients, or sea anemones can tolerate the constant change between underwater and dry environments in intertidal zones, apparently also depends on close cooperation with their bacterial symbionts. Life scientists around the world are currently investigating the manner in which the symbiotic interaction of microorganisms and hosts, in the functional unit of a metaorganism, supports the colonisation of such extreme habitats. An international research team under the leadership of the Collaborative Research Centre (CRC) 1182 "Origin and Function of Metaorganisms” at Kiel University has now presented an inventory of mechanisms, with which the interactions of hosts and symbionts support life under extreme environmental conditions, or even make it possible at all. Together with colleagues from Saudi Arabia’s King Abdullah University of Science and Technology (KAUST), the researchers have now described in detail for the first time in the scientific journal Zoology how microorganisms can promote the growth and the evolutionary fitness of different organisms in extreme locations.
An important factor in response to changing living conditions is time. If the environment at a particular place changes very quickly, for example through drastic change in physical and chemical conditions such as light or oxygen levels, the more highly-developed multicellular organisms in particular find the adjustment difficult. Their ability to adapt is too slow, because the required genetic change can only be completed over the course of several generations. "Here microorganisms can give their host organisms an advantage," emphasised Professor Thomas Bosch, cell and developmental biologist at Kiel University and spokesperson for the CRC 1182. "With bacteria, for example, the evolutionary processes occur much more rapidly. They can partially transfer this ability to respond much faster to environmental changes to their hosts, and thereby assist the hosts with adaptation," continued Bosch.
The lack of food or the inability to actually use the available nutrients further limits the available habitats. The metabolisms of many organisms are geared to specific optimal living conditions, and struggle to cope in extreme areas. Here too, it is often the symbiotic relationships with bacteria which enable plants and animals to expand the functioning of their own metabolisms. Thus, different organisms can, for example, exchange nutrients with their bacterial partners, and thereby utilise food sources which their metabolisms otherwise could not process.
Certain symbiotic bacteria, which colonise the roots of plants, help them to absorb elements such as nitrogen and other minerals in dry and nutrient-poor locations. Other bacteria support plant growth by increasing tolerance to saline soil. In the future, researchers will focus on investigating such helpful bacterial cultures, regarding their applicability to crops. Potentially, a better understanding of plants as metaorganisms could also help to utilise previously-unusable deserts for agriculture in the future.
In addition, microbial symbionts enable various organisms to develop a high tolerance towards a rapidly-changing environment: fixed cnidarians in the inter-tidal zones of different oceans can, for example, quickly adapt to the extreme changes in their living conditions because they can also abruptly change the composition of their bacterial colonisation. Behind this lie mechanisms such as the direct exchange of genetic information between different bacterial species, which controls the exclusion or inclusion of specific types of bacteria in the metaorganism. "In sea anemones, their bacterial colonisation changes in accordance with the prevailing site conditions," emphasised Dr Sebastian Fraune, research associate at the Zoological Institute at Kiel University. "The organisms can potentially save this flexible bacterial configuration, and recall it in the event of a change in their habitat, in order to cope with the new conditions," continued Fraune.
From the investigation of this bacterial-controlled ability to adapt to fast-changing environmental conditions, it may be possible in future to draw conclusions about the effects of climate change on organisms and ecosystems, or even to deduce adaptation strategies. Further research will clarify how the health and fitness of a metaorganism depend on the adaptability of its individual partners, and what effects arise from changing individual elements of this complex structure. The new findings thus emphasise the fundamental importance of researching the multi-organismic relationships between hosts and microorganisms, in particular, too, for the understanding of life in a variable and extreme environment.
Corinna Bang, Tal Dagan, Peter Deines, Nicole Dubilier, Wolfgang J. Duschl, Sebastian Fraune, Ute Hentschel, Heribert Hirt, Nils Hülter, Tim Lachnit, Devani Picazo, Lucia Pita, Claudia Pogoreutz, Nils Rädecker, Maged M. Saad, Ruth A. Schmitz, Hinrich Schulenburg, Christian R. Voolstra, Nancy Weiland-Bräuer, Maren Ziegler, Thomas C.G. Bosch (2018): Metaorganisms in extreme environments: do microbes play a role in organismal adaptation? ZoologyDOI: 10.1016/j.zool.2018.02.004
Prof. Thomas Bosch
Zoological Institute, Kiel University
Tel.: +49 (0)431-880-4170
Priority research area “Kiel Life Science”, Kiel University
Collaborative Research Centre (CRC) 1182 "Origin and Function of Metaorganisms", Kiel University:
KAUST news release on the related „Metaorganism Frontier Research Workshop“: