In ecosystems, a wide variety of organisms do not live independently but often construct symbiotic relationships to adapt to their habitats. For instance, many stinkbugs (Insecta: Hemiptera) possess a well-developed symbiotic organ within their digestive tract, hosting symbiotic bacteria that play a critical role in their survival and growth.
A research team including Principal Researcher Takema Fukatsu of the Molecular Biosystems Research Institute at the National Institute of Advanced Industrial Science and Technology (AIST) conducted experiments using the stinkbug (Plautia stali) and Escherichia coli (E. coli). They discovered that functional disruption of a single enzyme gene can transform E. coli into a symbiotic bacterium that resides in the insect's gut and supports its growth and survival. In this study, the research group found that in stinkbugs infected with E. coli that had been evolved to become symbiotic, the internal concentration of tryptophan (Trp), one of the essential amino acids, rose drastically, while the expression level of the Trp-degrading enzyme gene in the E. coli decreased remarkably. They also showed that the internal concentration of indole, a toxic organic compound produced when Trp is broken down, was significantly reduced. Furthermore, when they examined the genomic sequences of various gut symbiotic bacteria that support the survival of stinkbugs in the wild, they discovered that these bacteria had completely lost their Trp-degrading enzyme genes.
These results empirically demonstrate that the evolution of symbiotic bacteria, which was previously thought unlikely to happen easily, can occur through the loss of function in a single enzyme gene (the Trp-degrading enzyme), and they clarify its metabolic foundation. Moving forward, this breakthrough is expected to enable applications in technologies aimed at creating and designing symbiosis.
(Article: Masanori Nakajo)
