Study of insect bacteria reveals genetic secrets of symbiosis

June 20, 2013

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 prestigious 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.

How can this be?

"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."

The research team also examined a strain of Tremblaya that doesn't have Moranella living inside it. This variety employs about 50 more genes than the one containing Moranella, which strongly suggests Moranella plays a key role in allowing the insect-dwelling Tremblaya to operate with such a tiny genome.

McCutcheon said Tremblaya, with its shrinking genome, in many ways resembles organelles called mitochondria - tiny structures found within all plant and animal cells that scientists believe started out as symbiotic bacteria in the early history of life. The mealybug/bacteria relationship he studies may illustrate one pathway bacteria take in becoming essential and highly integrated components of other cells.

"So this research really touches on some fundamental questions of the origin of life," he said. "It's exciting to see if we can get some insight into the origin of organelles."

McCutcheon said this study involved an international cast of 12 collaborators. Filip Husnik, the study's lead author, is a Czech doctoral student from the University of South Bohemia who worked in McCutcheon's UM lab. Other team members were from Japan, England, California, Utah and Florida.

The study was funded by a $529,000 grant from the National Science Foundation.

"Our work illustrates how an animal's interactions with bacteria can drive hidden organismal complexity," McCutcheon said. "A tree is more than a tree, and an animal is more than an animal. They are really mosaics of plants and animals and bacteria all working together."
-end-


The University of Montana

Related Bacteria Articles from Brightsurf:

Siblings can also differ from one another in bacteria
A research team from the University of Tübingen and the German Center for Infection Research (DZIF) is investigating how pathogens influence the immune response of their host with genetic variation.

How bacteria fertilize soya
Soya and clover have their very own fertiliser factories in their roots, where bacteria manufacture ammonium, which is crucial for plant growth.

Bacteria might help other bacteria to tolerate antibiotics better
A new paper by the Dynamical Systems Biology lab at UPF shows that the response by bacteria to antibiotics may depend on other species of bacteria they live with, in such a way that some bacteria may make others more tolerant to antibiotics.

Two-faced bacteria
The gut microbiome, which is a collection of numerous beneficial bacteria species, is key to our overall well-being and good health.

Microcensus in bacteria
Bacillus subtilis can determine proportions of different groups within a mixed population.

Right beneath the skin we all have the same bacteria
In the dermis skin layer, the same bacteria are found across age and gender.

Bacteria must be 'stressed out' to divide
Bacterial cell division is controlled by both enzymatic activity and mechanical forces, which work together to control its timing and location, a new study from EPFL finds.

How bees live with bacteria
More than 90 percent of all bee species are not organized in colonies, but fight their way through life alone.

The bacteria building your baby
Australian researchers have laid to rest a longstanding controversy: is the womb sterile?

Hopping bacteria
Scientists have long known that key models of bacterial movement in real-world conditions are flawed.

Read More: Bacteria News and Bacteria Current Events
Brightsurf.com is a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for sites to earn advertising fees by advertising and linking to Amazon.com.