Bacteria connect to exchange nutrients
Scientists have discovered a new way of how bacteria can achieve nutritional exchange and published their results of research in the scientific journal Nature Communications.
Bacteria usually live in species-rich communities and
frequently exchange nutrients and other metabolites. Until now, it was unclear whether microorganisms exchange metabolites exclusively by releasing them into the surrounding environment or whether they also use direct connections between cells for this purpose. Scientists from
the Research Group Experimental Ecology and Evolution at the Max Planck Institute for Chemical Ecology in Jena, Germany, and their colleagues at the universities of Jena, Kaiserslautern, and Heidelberg addressed this question using the soil bacterium Acinetobacter baylyi and the gut microbe Escherichia coli and published their results
in the journal Nature Communications. By experimentally deleting bacterial genes from the genome of both species, the scientists generated mutants that were no longer able to produce certain amino acids, yet produced increased amounts of others.
Collective Strength
In co-culture, both bacterial strains were able to cross-feed each other, thereby compensating the experimentally induced deficiencies. However, separating the two bacterial strains with a filter that allowed free passage of amino acids, yet prevented a direct contact between cells, abolished growth of both strains. This experiment showed that a direct contact between cells was required for the nutrient exchange to occur. Observing the co-culture under the electron microscope revealed structures that formed between bacterial strains, which functioned as nanotubes and enabled the exchange of nutrients between cells. Especially remarkable, however, was the fact that only the gut microbe Escherichia coli was capable of forming these structures and connecting to Acinetobacter baylyi or other E. coli cells.
"The major difference between both species is certainly that E. coli is able to actively move in liquid media, whereas A. baylyi is immotile. It may thus be possible that swimming is required for E. coli to find suitable partners and connect to them via nanotubes," explains Christian Kost, head of the Research Group Experimental Ecology and Evolution, which is funded by the Volkswagen Foundation in its expiring funding initiative
"Evolution Biology". His research focuses mainly on the question why organisms cooperate with each other.
"Hungry" Cells Spring into Action
"A lack of amino acids triggered the formation of nanotubes. Deleting a gene, which is involved in the production of a certain amino acid, caused the resulting bacteria to connect to other bacterial cells and − in this way − compensate their nutritional deficiency. However, nanotubes did not form when the required amino acids were supplemented to the growth medium, indicating that the formation of these structures obviously depends on how 'hungry' a cell is," the scientist summarizes.
Cells that specialize on particular biochemical processes and thereby divide their labor can be advantageous for bacterial communities: Resources can be used more economically, thus enhancing growth and efficiency. "To me, the most exciting question that remains to be answered is whether bacteria are in fact unicellular and relatively simply structured organisms or whether we are actually looking at some other type of multicellularity, in which bacteria increase their complexity by attaching to each other and combining their biochemical abilities," Christian Kost summarizes.
Original Publication:
Pande, S., Shitut, S., Freund, L., Westermann, M., Bertels, F., Colesie, C., Bischofs, I. B., Kost, C.. Metabolic cross-feeding via intercellular nanotubes among bacteria. Nature Communications.
