Network-like structures built by bacteria inside insect cells to feed more efficiently
The cereal weevil, one of the world’s main crop pests, harbors symbiotic bacteria that live inside its cells. Scientists from INRAE and INSA Lyon, in collaboration with experts from the SOLEIL Synchrotron and Claude Bernard University in France, as well as the Max Planck Institute and EMBL in Germany, have discovered that these bacteria build complex, network-shaped membrane structures. These structures increase their surface area for exchange with the host cell, allowing the bacteria to absorb an essential nutrient: sugar.
This is the first time that bacterial structures of this scale have been observed. The SOLEIL’s HERMES beamline contributed to this discovery.
The cereal weevil is one of the major pests affecting cereals such as wheat, rice, and maize, both in the field and in storage. It feeds directly on the grains, but it is not alone: it hosts symbiotic bacteria that live inside its cells. These bacteria, named Sodalis pierantonius, reside in large numbers within specialized insect cells. They provide the weevil with essential nutrients that are absent from its cereal-based diet. This is a mutually beneficial relationship: the bacteria use the sugars produced during the digestion of grains and, in return, supply the insect with essential nutrients such as vitamins and certain amino acids.
While scientists have long understood the importance of this exchange, its exact mechanisms remained unknown. To investigate, the researchers used electron microscopy with an advanced sample preparation method that preserves membranes more effectively. For the first time, the team observed original tubular patterns forming complex membrane structures built by the bacteria. To study the architecture and composition of these structures, the scientists developed new 3D microscopy and analytical methods using the SOLEIL Synchrotron particle accelerator.
Read more on the SOLEIL website
Image: Scale 200 nm. Transmission electron microscopy image showing intracellular symbiotic bacteria from the cereal weevil Sitophilus oryzae. The bacteria form a three-dimensional network of tubular structures, called tubenets. These structures enhance host–bacterium nutritional exchanges, allowing efficient transfer of sugars from the host’s diet to the symbiotic bacteria. In purple, an example of a bacterium and its tubenets can be seen within the cytoplasm of the host cell.