How beewolves protect their symbiotic bacteria from toxic nitric oxide

Scientists from the Max Planck Institute for Chemical Ecology in Jena and Johannes Gutenberg University in Mainz, Germany, have unveiled fascinating insights into the symbiotic relationship between beewolves and their bacterial companions.

Beewolves, a type of solitary digger wasp, maintain a unique association with symbiotic bacteria residing in their antennae. These beneficial bacteria play a crucial role in safeguarding beewolf larvae from harmful molds by generating an antibiotic mixture comprising an impressive array of up to 49 different substances.

During their reproductive process, female beewolves skillfully capture honeybees, paralyze them with a potent sting, and transport them to carefully constructed underground brood cells. Subsequently, the females lay their eggs upon the immobilized bees, serving as nourishment for the hatching larvae. As an intriguing aspect of this symbiosis, female beewolves also deposit symbiotic bacteria in a white mass on the ceiling of the brood cells.

The study has uncovered a remarkable aspect of this mutualistic relationship. Beewolf eggs emit toxic nitric oxide, which acts as a disinfectant for the brood cavity. However, the symbiotic bacteria are shielded from this toxicity, thanks to a protective barrier provided by a white secretion originating from the female beewolves’ antennae, wherein the symbionts are also found. This diffusion barrier ensures the safety of the symbiotic bacteria while facilitating the crucial disinfection process carried out by the beewolf eggs.

This research sheds light on the intricate mechanisms underlying the intricate cooperation between beewolves and their bacterial allies, providing essential insights into the fascinating world of insect symbiosis and host-bacteria interactions.

Beewolf eggs emit toxic nitric oxides to keep brood cells mold-free

The survival of beewolf offspring and their prey, the bees, is constantly threatened by the rapid growth of mold fungi in the moist soil of the brood cell. These fungi can significantly reduce the storage life of the larva’s food source, posing a serious risk to the developing beewolf larvae. Previous studies have revealed that beewolf eggs release a toxic gas called nitric oxide to counteract and kill the mold fungi in the brood cell.

While nitric oxide is commonly known to humans as a component of car exhaust and can be harmful to our respiratory system and oxygen transport, beewolf eggs utilize its toxic properties to disinfect the environment in which they develop, protecting against potential pathogens. Interestingly, the brood cell also houses the beewolf’s beneficial symbiotic bacteria, which play a crucial role in producing antibiotics to safeguard the larvae from molds.

The researchers, led by Tobias Engl from the Max Planck Institute for Chemical Ecology, sought to understand how the symbiotic bacteria managed to survive the onslaught of toxic gas released by the beewolf eggs. Initially, they speculated that the bacteria might have developed protective mechanisms to avoid being poisoned by the nitric oxide. This assumption was backed by their observation that the bacteria’s genes related to gas protection were up-regulated when tested in a controlled, artificial environment outside the natural brood cell, such as in a petri dish.

However, further investigation revealed an intriguing twist. When subjected to the high concentrations of nitric oxide present in the actual brood cell, the symbiotic bacteria did not show the same protective response as observed in the artificial setting. Despite the potential danger, these remarkable bacteria managed to survive and thrive alongside the beewolf eggs without deploying the anticipated defense mechanism.

The study’s second lead author, Chantal Ingham from the Johannes Gutenberg University in Mainz, emphasized that the response of the symbiotic bacteria to nitric oxide was insufficient to account for their survival within the brood cell. This puzzling discovery indicates that there may be other, yet unknown, mechanisms at play, enabling the bacteria to coexist harmoniously with the beewolf eggs in this challenging and dynamic environment. The intricate interplay between beewolves, their symbiotic bacteria, and the protective role of nitric oxide continues to captivate researchers, and further investigations are underway to unravel this captivating mystery.

Hydrocarbons in the beewolf’s antennal gland secretions provide protection against toxic nitric oxide

The scientists’ quest for answers reached a breakthrough when they closely examined the enigmatic white substance secreted from the antennal glands of female beewolves. Focused on understanding the impact of this secretion and its hydrocarbon components on toxic nitric oxide, the research team made significant strides in unraveling the mystery.

Through meticulous experiments, they discovered that the hydrocarbons present in the beewolf’s antennal gland secretion create a protective shield around the symbiotic bacteria, effectively blocking the diffusion of nitric oxide. This ingenious defense mechanism ensures that the bacteria remain unharmed by the toxic gas, safeguarding them during the critical phase of transmission from one generation of beewolves to the next.

Lead author Tobias Engl expressed the significance of this finding, hailing it as a rare example illustrating how insects can actively shield their own symbionts during this vulnerable phase of transition. The hydrocarbons, which usually serve as vital protection against desiccation, natural enemies, and chemical communication in insects, have now revealed yet another exciting function in safeguarding symbiotic relationships.

In the insect world, many species pass on their symbiotic bacteria to successive generations. However, the survival of these symbionts outside their host’s body during transmission has remained largely mysterious. The beewolf symbiosis has emerged as an enthralling case study showcasing mutual protection. The symbiotic bacteria diligently safeguard the beewolves from pathogens by producing essential antibiotics. In return, the beewolves, aware of their own defenses against pathogens, have developed the remarkable ability to produce a layer of hydrocarbons that shield and preserve their symbionts.

For study leader Martin Kaltenpoth, who leads the Department of Insect Symbiosis at the Max Planck Institute in Jena, the beewolf symbiosis represents a captivating example of mutualistic protection, where both parties benefit from the alliance.

The fascinating mechanism discovered in this research demonstrates how these resourceful digger wasps adeptly defend themselves against pathogens while nurturing and preserving their essential bacterial helpers. As the researchers move forward, further experiments will explore the unique hydrocarbon mixture employed by beewolves, investigating whether specific hydrocarbons are particularly well-suited to protect the symbionts or if a range of hydrocarbons can fulfill this critical task. This ongoing investigation promises to deepen our understanding of the remarkable symbiotic relationships that thrive in the natural world.

Source: Max Planck Society

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