Endosymbiosis has had a profound impact on the evolution of life, endowing organisms with new biochemical capabilities and promoting innovation and diversification. However, the birth of new endosymbioses is very rare and it is difficult to trace their origins. Recently, Julia A. Vorholt’s team at the Swiss Federal Institute of Technology in Zurich (ETH Zurich) made a major breakthrough in studying the beginning of this special relationship between two organisms and published a paper titled “Inducing novel endosymbioses by implanting bacteria in fungi” in Nature. Through microinjection technology, they transplanted bacteria into the filamentous fungus Rhizopus microsporus to induce a completely new artificial endosymbiotic relationship. This discovery opens up new opportunities for designing synthetic endosymbionts with ideal characteristics and provides new insights into the mechanisms of understanding the evolution of endosymbiosis.
Abstract:
The study presents an experimental approach to induce novel endosymbiotic relationships between bacteria and fungi by directly implanting bacteria into fungal cells. The researchers used a model system consisting of the fungus _Rhizopus microsporus_ and the bacterial endosymbiont _Mycetohabitans rhizoxinica_. They employed Fluidic Force Microscopy (FluidFM) to inject bacteria into fungal germlings, allowing for real-time tracking and analysis of the early stages of endosymbiosis under stabilizing selection pressure. The results show that the implanted bacteria can be vertically transmitted and that adaptive laboratory evolution can increase the stability of the induced endosymbiosis, demonstrating the potential for synthetic biology approaches to create designer endosymbionts.
Background:
Intracellular endosymbioses are close interactions between organisms where two metabolic networks are integrated, often leading to major evolutionary transitions. Endosymbioses can benefit the host by providing chemical defense systems, unlocking essential nutrients, or accessing new energy sources. However, establishing de novo endosymbiogenesis is challenging due to obstacles such as immune responses and growth synchronization. Studying natural partnerships, like mitochondria and chloroplasts, has provided insights into endosymbioses, but the early steps remain elusive. This work reports a procedure to implant bacteria into R. microsporus that enabled real-time tracking using confocal microscopy and characterizing early adaptations in the endosymbiosis under stabilizing selection pressure.
Materials and Methods:
The researchers used the filamentous fungus _Rhizopus microsporus_ and its endosymbiont _Mycetohabitans rhizoxinica_ as a model system. They applied FluidFM to inject bacteria into fungal cells, bypassing the natural entry process. This technique allowed for the implantation of 1–30 bacteria per injection event into _R. microsporus_ germlings. The researchers then used confocal microscopy to track the bacteria in real-time and characterize early adaptations. They also employed fluorescence-activated cell sorting (FACS) to classify spores for their colonization status and to sort spores containing bacteria for further propagation.
Results:
The study confirmed that both partners survived the injection procedure, and the bacteria were able to colonize the fungal cells. The researchers observed that _M. rhizoxinica_ could be vertically transmitted in _R. microsporus_ strain NH, which naturally does not harbor endosymbionts. An adaptive laboratory evolution experiment showed that the artificially induced endosymbiosis could be stably propagated in the new host upon positive selection, with an increase in the fitness index of the endosymbiosis over time. The researchers also detected the production of rhizoxin, a compound produced by the endosymbiont, in the induced endosymbiosis, indicating the transfer of metabolic capabilities to the new host.
Conclusion:
The study successfully demonstrated the induction of novel endosymbioses by implanting bacteria into fungi, providing a platform for real-time investigation of initial endosymbiotic events. The findings show that adaptive evolution can increase the stability of induced endosymbiosis, despite high initial costs, and that the ability to initiate endosymbioses can advance synthetic biology approaches towards designer endosymbionts. This work sheds light on the evolutionary forces shaping endosymbiogenesis and has biotechnological implications for creating endosymbiotic relationships with desired traits.
Post time: Feb-12-2025