Cicada Symbiotic Complexes of Bacteria Are Different from Any Known Organism

University of Montana (UM) researchers have made a discovery at the cellular level to help understand the basic processes of all life on our planet - this time within the unusual bacteria that has lived inside cicada insects since dinosaurs roamed Earth. During the past 70 million years, the bacteria underwent extreme adaptations to live within the insects' bodies, losing between an estimated 95 to 97 percent of their genes and resulting in some of the smallest genomes known to any organisms. In the process, they lost the ability to live anywhere outside of cicadas. "Cicada symbiotic complexes are very different from any other known organism," said Matt Campbell, a UM graduate student who studies cicadas in UM Biology Associate Professor John McCutcheon's lab, based in the Division of Biological Sciences. Many insects live in very close associations with symbiotic bacteria. These bacterial symbioses are critically important for insects that consume only one type of food that is missing some essential nutrients. Examples include blood-feeding lice, as well as insects that feed on plant sap - aphids, leafhoppers, and cicadas. The UM research has shown that cicadas' symbiotic bacteria produce amino acids and vitamins that their insect hosts require to grow and reproduce. During three field seasons studying a South American cicada, UM postdoctoral researcher Dr. Piotr Lukasik found that many of the species' single symbiotic bacterium evolved into complexes of several different types of bacterium in the same cicada. "Through that process, individual bacteria have lost many genes and now depend on each other because every type contains unique, essential genes," Dr. Lukasik said.
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