Symbiotic bacteria in grain weevils build tubular networks for survival

Unprecedented networked membrane systems dramatically increase bacterial surface area, enhancing nutrient exchange between bacteria and their hosts

November 04, 2025

Grain weevils of the genus Sitophilus are major crop pests that harbor symbiotic bacteria within their cells. In collaboration with experts from the SOLEIL Synchrotron and Claude Bernard University in France, the Department of Insect Symbiosis at the Max Planck Institute for Chemical Ecology, and the European Molecular Biology Laboratory (EMBL) in Germany, scientists from the National Research Institute for Agriculture, Food and Environment (INRAE) and the National Institute of Applied Sciences (INSA) in France found that these bacteria construct intricate membrane networks. These structures increase the surface area for exchange with the host cell, enabling the bacteria to recover an essential nutrient, sugar. This is the first time structures of this scale have been discovered in bacteria. The findings, published in Cell, open new avenues of research to better understand microorganisms, particularly intracellular ones, and offer new approaches to fighting insect pests.

To the point:

Highly magnified electron microscope image showing a purple-stained circular structure with a scale bar indicating 200 nm. — This transmission electron microscopy image shows the intracellular symbiotic bacteria of the rice weevil (*Sitophilus oryzae*). The bacteria form a three-dimensional network of tubular structures called "tubenets." This increases the nutritional exchange between the host and the bacteria, enabling the efficient transfer of sugars from the host's food to the symbiotic bacteria. The bacteria and their tubenets within the host cell's cytoplasm are colored purple.

© INRAE - Séverine Balmand, Laboratoire BF2i

This transmission electron microscopy image shows the intracellular symbiotic bacteria of the rice weevil (*Sitophilus oryzae*). The bacteria form a three-dimensional network of tubular structures called "tubenets." This increases the nutritional exchange between the host and the bacteria, enabling the efficient transfer of sugars from the host's food to the symbiotic bacteria. The bacteria and their tubenets within the host cell's cytoplasm are colored purple.

© INRAE - Séverine Balmand, Laboratoire BF2i

Grain weevils, major global crop pests, host symbiotic bacteria inside their cells—relationships critical to the pests’ survival and success.
Scientists discovered that these bacteria form complex, networked membrane structures—a previously unknown architectural feature.
These intricate membrane networks dramatically increase surface area, enhancing nutrient exchange with the host insect and enabling the bacteria to efficiently recover essential sugar, a vital resource for both symbiont and pest.
This is the first time such large-scale, organized membrane systems have been observed in bacteria, challenging long-held views on bacterial cellular architecture.

Intracelluar symbiotic bacteria as nutrient providers for grain pests

Sitophilus weevils are pests that attack cereal crops such as wheat, rice, and corn in fields and silos. The weevils have symbiotic bacteria, known as Sodalis pierantonius, that live in large numbers in specialized insect cells. The bacteria provide the weevils with essential nutrients that cannot be found in cereals. This relationship is mutually beneficial: the bacteria use the sugar produced during digestion, and in return, they provide the insect with essential nutrients such as vitamins and certain amino acids.

Although scientists recognized the importance of these exchanges, the process itself remained unknown. To study these interactions, the research team used electron microscopy and a sample preparation method that preserves membranes more effectively. This method allowed the research team to observe unique tubular patterns forming complex membrane structures built by the bacteria. To study these structures' architecture and composition, the scientists developed observation and analysis methods using 3D microscopy and the SOLEIL Synchrotron particle accelerator.

Tubenets - veritable exchange networks built by the bacteria

Analysis revealed that these structures form a complex network of tubes, each with a diameter of 0.02 micrometers (µm) and several micrometers in length that connect the bacteria with numerous interconnections. Similar to how microvilli in the human intestine increase the surface area for absorbing nutrients during digestion, these tubular structures increase the surface area of the bacteria for exchanging nutrients with host cells. This enables the bacteria to better assimilate sugar. In exchange, the bacteria produce essential nutrients for the cell. The research team named these structures "tubenets," combining "tube" and "network" to reflect their shape.

Although scientists are familiar with structures that increase the surface area for nutrient absorption in multicellular organisms, such as intestines and plant roots, this is the first time that this type of structure has been identified in bacteria. Similar structures may exist in other types of bacteria and allow them to acquire nutrients more efficiently.

The findings open new frontiers in understanding intracellular symbiosis and may lead to innovative, sustainable strategies to disrupt pest-microbe interactions.