Carl Zimmer, whose biography is too long to list here, recently wrote a New York Times article about some of the smallest cellular genomes documented to date. In the article, he describes one symbiotic microbe, "Ca. Tremblaya princeps", which lives in the gut of a mealybug and helps to digest its diet of tree sap. Tremblaya's genome is a mere 120 genes - a very small fraction of the human genome, which contains around 21,000 genes.
As if that weren't interesting enough, researchers discovered that Tremblaya itself has a symbiotic microbe living within its cell walls - "Ca. Moranella endobia". Moranella, which has over 400 genes, provides complementary genes that Tremblaya needs to function and produce essential amino acids. This unprecedented relationship is reminiscent of Russian nesting dolls (matryoshka), or as one blogger aptly noted, "snug as a bug in a bug in a bug".
Each organism in this trio depends on the other to survive, and by working together in this way for many millions of generations, each adapted to the arrangement by shedding unnecessary or redundant genes so they could focus on what they do best.
Time and technology will surely reveal other nested symbionts or unique co-relationships, but in the meantime, let your imagination run wild. If you could create a creature with a symbiont that had its very own symbiont, what would it look like, and how would it function?
By: BioTek Instruments