Mealy bugs are a common sight on plants, sucking the sap for food.
But few people wonder what actually goes on inside their little gray bodies.
John McCutcheon, an assistant professor in the Division of Biological Sciences at the University of Montana, recently published a two-year study about citrus mealy bugs and their symbiotic relationship with two bacteria in the prestigious science journal Cell.
Though these bland insects fade from human eyesight, McCutcheon finds them fascinating because they don’t have a typical symbiotic relationship with the bacteria living inside them. Nor do they make amino acids, an essential nutrient in all animals, the most common way, McCutcheon said.
“There are 20 amino acids and most animals make 10 of them,” McCutcheon said.
The other 10 are usually supplied through the food animals ingest. But some, like the mealybug, need extra help when they can’t generate the necessary nutrients on their own or obtain them from their food supply, McCutcheon said.
So that’s where the two bacteria emerge in the amino acid assembly line. Known as Moranella and Tremblaya, these bacteria dwell within mealy bugs’ cells.
The bacterium Tremblaya is one of the smallest genomes ever discovered, containing only 120 genes, compared to E. coli, which holds 4,000, McCutcheon said.
But a closer look revealed that another bacterium, Moranella, resides in the Tremblaya cytoplasm.
“It’s a version of Russian nesting dolls,” McCutcheon said.
All three combine in the amino acid process, but also get more genetic assistance from an additional three genomes from the mealy bug, creating a complicated six-way relationship that McCutcheon hopes to examine further.
The study grew out of another paper published in 2011 that McCutcheon worked on. Filip Husnik, lead author and Czech Republic doctoral student, propelled the study further that summer, which resulted in the paper published in Cell.
It’s only been recently that scientists have looked at the complex relationships between animals, insects and bacteria, McCutcheon said. The deceptively straightforward process contains more questions that McCutcheon hopes to continue asking.
“We’re trying to figure out how the world works,” McCutcheon said. “We study the extreme relationships to explain generalities.”