Natures wonders: triple symbiosis (Introduction)

by David Turell , Wednesday, September 09, 2015, 14:21 (3361 days ago) @ David Turell

Mealy bugs survive because they have onboard two bacteria, one inside the other, to produce the necessary amino acids to survive and to share genes:-http://www.sciencedaily.com/releases/2013/06/130620142954.htm-"Mealybugs only eat plant sap, but sap doesn't contain all the essential amino acids the insects need to survive. Luckily, the bugs have a symbiotic relationship with two species of bacteria -- one living inside the other in a situation unique to known biology -- to manufacture the nutrients sap doesn't provide.-"The net result: The bacteria get a comfy mealybug home, and the bugs get the nutrition they need to live.-"University of Montana microbiologist John McCutcheon describes such mutually beneficial relationships used to solve life's little problems as "almost hilariously complicated. But animal-bacterial relationships are extremely common in nature, and it's my goal in life to help people understand that it's normal."-"McCutcheon and his research partners recently delved deeper into the genes involved in the "tripartite nested mealybug symbiosis," and their work was published in the June 20 issue of Cell, a scientific journal. The researchers discovered the already complex three-way symbiosis actually depends on genes from six different organisms -- three more than the number of species that currently exist in the symbiosis.-"Tremblaya princeps is the larger of the two bacteria species living within special organs inside mealybugs. Tremblaya houses the smaller bacterial species, Moranella endobia, within its cytoplasm. But what makes Tremblaya truly odd is the size of its genome, or genetic code. With only 120 genes, its genome is the smallest known and smaller than many scientists consider necessary for life. By comparison, common E. coli bacteria have about 4,200 genes and humans have about 21,000.-"'We wanted to discover how this genome got so small," McCutcheon said. "We suspected Tremblaya's genome may have gotten smaller by transferring genes to the host animal, which is called horizontal transfer."-"The researchers looked for genes in the mealybug genome that resemble bacteria genes. However, after extensive analysis they only found one weak possibility for horizontal transfer from Tremblaya.-"'Our hypothesis that Tremblaya was transferring genes to the host was dead wrong," said McCutcheon. They did, however, find 22 other bacterial genes mixed in with the mealybug code -- genes that seem to support activities missing in Tremblaya, Moranella and the mealybug.-"'The genes are probably from historical bacterial infections," McCutcheon said. "These bacteria are no longer present in the mealybugs we work with, but their horizontally transferred genes are, and these genes allow the symbiosis to work.'"