To really understand the system, you've got to assign the different bits of DNA to organisms. “But this black-box ecology just does not work well. “When doing this type of forensic metagenomics, some scientists suggest you can just analyze the whole system as one unit-a so-called ‘black-box' approach-without knowing which piece of DNA came from which organism,” Eisen says. muelleri, the team found all the essential amino acid synthesis pathways. Sure enough, when they pooled the bits of sample DNA that came from S. A large amount of the leftover DNA mapped to another bacterium, S.
Realizing the amino acid pathways might be carried out by other bacteria living inside the insect, the team began picking through their forensic samples of DNA sequences, removing all the sequence reads that matched neither the insect nor its known symbiotic B. Could there be something else, some other bacteria, adding these essential ingredients? Was the sharpshooter somehow cranking out its own amino acids? Doubtful. Could the plant be somehow providing amino acids to its insect predator? Unlikely. The scientists were dumbstruck to find no evidence of the biochemical pathways needed to synthesize amino acids. cicadellinicola 's genome from material gathered via dissections of hundreds of insects. In the study, the team first carried out a painstaking forensic type of DNA analysis known as “metagenomics,” in which they sequenced the B. “My initial interest in sharpshooter symbiosis was in the hope that we could find out exactly how xylem can be used as food,” Moran explains. University of Arizona evolutionary biologist Nancy Moran, who has extensively studied the co-evolution of insects and their resident bacteria, recruited Eisen to the current project. cicadellinicola ), as does the biologically similar aphid. But researchers had assumed that the sharpshooter needed just one bacterial symbiont (in this case, B. These sap-feeders are often known to rely on resident bacteria for a balanced diet – especially the synthesis of the “essential” amino-acids that all animals, including humans, cannot make for themselves. Many insects, such as aphids and cicadas, feed on the sap from a plant's xylem or phloem, pipes that transport water and food within a plant. In particular, in this case, the threesome came as a surprise. We knew symbionts were doing something for this insect-but until this study, we had no clue what that was.” “In order to design methods to fight the insect, we've got to understand how it works and its weaknesses. “Much as mosquitoes transmit malaria, the sharpshooter transmits plant disease, including Pierce's disease, which threatens vineyards,” Eisen says. The sharpshooter channels the sweets from sap to the bacteria, which in turn feed the insect vitamins, cofactors, and essential amino acids. In the study, a team of scientists led by TIGR microbiologist Jonathan Eisen, now at the University of California, Davis, uncovered an intimate metabolic co-dependency among the glassy-winged sharpshooter ( Homalodisca coagulata ) and two bacteria, Baumannia cicadellinicola and Sulcia muelleri. Although insect-bacteria symbiosis is common, this is the first genomic analysis of three partners.
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