Research reveals a unique way in which a bacterium hitches a ride on the venom of a parasitic wasp to pass from generation to generation, offering a new direction for studying the interactions between insects and microorganisms
New research from the University of Haifa – Oranim Campus, published in the prestigious scientific journal Current Biology, found an unusual mechanism for transferring symbiotic bacteria from generation to generation through wasp venom. The researchers discovered that the bacterium Sodalis praecaptivus subsp spalangiae settles in the venom gland of the parasitic wasp Spalangia cameroni, and is transferred along with the venom into a fly pupa, where it manages to survive and spread.
“In most interactions between insects and bacteria that live with them in symbiosis, the bacteria are passed from generation to generation directly through the insect’s eggs. To our surprise, we found that this bacterium is not found in the wasp’s eggs, but rather uses the wasp’s venom to pass from generation to generation. The venom is a very hostile environment for bacteria, as it is acidic and contains antibacterial substances, and yet the bacteria manages to survive there and establish itself in the young wasp’s body,” said Dr. Sarit Rochkin Shalom, one of the study’s authors.
The wasp Spalangia cameroni is a small parasitic wasp (about 4 mm) that attacks the pupae of flies, including the house fly. The wasp locates a fly pupa, injects venom into it, and then lays an egg on it. The larva that hatches from the egg feeds exclusively on the fly pupa until it develops into an adult wasp. In the current study, they sought to Dr. Elad Hil And Dr. Sarit Ruchkin, hello, how are you?Department of Biology and Environment At the University of Haifa - Oranim Campus, together with researchers from the Max Planck Institute in Germany and the University of Utah in the United States, to examine how the Sodalis bacterium is passed from generation to generation in this wasp.
The results of the study indicate that the Sodalis bacterium is located in the venom gland of the adult wasp, and when the wasp attacks a fly pupa, it is injected along with the venom. The bacterium survives and multiplies inside the fly pupa until the young wasp larva begins to feed on it. During the digestion process, the bacterium penetrates the larva's tissues, spreads throughout its body, and finally reaches the venom gland of the adult wasp again. In this way, it is transmitted in a stable and cyclical manner to future generations.
The research team is currently studying the mechanisms that allow the Sodalis bacterium to survive in the wasp venom environment and use it as a means of transmission. So far, such a pathway has only been documented in one other species of parasitic wasp, which raises the possibility that it is more common in nature than is currently known. In addition, it was found that the bacterium can also be transmitted through the sperm of males, although with low frequency. “When females inherit the bacterium from their father, they are able to pass it on through their venom. Paternal transmission of bacteria is a very rare phenomenon, which has been documented in only a few cases so far,” said Dr. Sarit Rochkin Shalom.
The researchers also found that the wasp Spalangia cameroni contains two additional bacterial species, but they are transmitted directly through the eggs and not through the venom. The difference may lie in the time over which the interactions between the insects and the various bacteria have evolved: while the two additional bacteria have lived inside the wasp cells for millions of years and have lost their ability to exist outside the host body, the symbiosis with the Sodalis bacterium is very young on an evolutionary scale and is therefore still able to reproduce outside the host cells, which allows it to exploit the venom as a means of transmission.
To test the specificity of the relationship between the wasp and the bacterium, the researchers infected the wasp with a closely related subspecies of Sodalis, but found that it failed to integrate into the venom gland in sufficient quantities and was not successfully passed on to offspring. When injected into the fly pupa, it did not survive and was unable to reproduce there, indicating that the bacterium found in the wasp had been specifically adapted to survive in and be transmitted through the venom.
“This mechanism may be a critical step in the early development of symbiosis between bacteria and insects,” the researchers explain. “Our findings show how bacteria can adapt and survive in suboptimal conditions, and they provide a fascinating new direction for studying the interactions between microorganisms and their hosts,” the researchers concluded.
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