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Update(MM/DD/YYYY):04/17/2023

Successful Evolution of E. coli into Insect Symbiotic Bacteria

– A single mutation makes ordinary bacteria into essential symbiotic bacteria that support survival of host stinkbug –

 
Researchers) KOGA Ryuichi, Group Leader, MORIYAMA Minoru, Senior Researcher, FUKATSU Takema, Prime Senior Researcher (also Research Director, ERATO FUKATSU Evolving Symbiosis Project), Symbiotic Evolution and Biological Functions Research Group, Bioproduction Research Institute

Points

  • Successful evolution of E. coli into insect symbiotic bacteria in the laboratory
  • With a single mutation, E. coli becomes essential bacterial symbiont that supports survival of host stinkbug
  • Surprisingly demonstrating that symbiotic evolution can occur quickly and easily

Figure of new research results

Figure: E. coli cells before and after the symbiotic evolution (insets), and adult stinkbugs Plautia stali infected with them
Before symbiotic evolution, E. coli cells are elongated in shape and the infected insects exhibit low emergence rate, small body size, and brown body color (left). After symbiotic evolution, E. coli cells become shorter, and the infected insects exhibit improved emergence rate, larger body size, and green body color (right).


Background

The study of symbiotic relationships between plants, animals, and microorganisms, including humans, has been developing significantly on an international scale, but almost all previous studies have focused on existing highly specialized symbiotic relationships. However, even the most highly specialized symbiotic microorganisms must have originally been free-living. How symbiotic relationships started and established, especially the evolutionary origins of sophisticated symbiotic relationships that are essential for the survival of the host organism, is a fundamental question to be addressed. However, considering that such evolutionary events must have occurred in the distant past, it has been regarded as difficult to investigate the research topic empirically.

On the other hand, in recent years, "experimental evolutionary studies" have been actively conducted to elucidate evolutionary processes and mechanisms in the laboratory in real-time, mainly using microorganisms. From such an approach, researchers are attempting to reproduce and understand such evolutionary processes as antibiotic resistance, heat tolerance, and attenuation/enhancement of infectivity and virulence to the host. However, it has been generally considered difficult to evolve highly mutualistic microorganisms in the laboratory that are essential for survival of the host organism, and there have been no such previous studies.

 

Summary

In collaboration with the University of Tokyo, researchers in AIST have shown that, by removing essential bacterial symbiont from the stinkbugs, infecting fast-evolving E. coli instead, and maintaining the symbiont-replaced stinkbugs continuously in the laboratory, E. coli can evolve into an essential symbiont that supports the survival of the host stinkbugs within a short period of time, ranging from a few months to a year, through a single mutation that disrupts a global transcriptional regulatory system.

This study demonstrated that the evolution of symbiotic microorganisms, which are essential for host survival, can occur more rapidly and easily than previously envisaged. It was groundbreaking that we successfully made E. coli, the best-studied model bacterium in molecular biology, evolve into a symbiotic bacterium. Using this insect-E. coli experimental symbiotic system, it is expected to greatly advance our understanding of the processes and mechanisms of symbiotic evolution in the future.





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