HAIFA, Israel — A new study from the University of Haifa – Oranim Campus, published in the prestigious scientific journal Current Biology, identified an unusual mechanism for the transmission of symbiotic bacteria from generation to generation through the venom of a wasp.
The researchers discovered that the bacterium (Sodalis praecaptivus subsp. Spalangiae) is located in the venom gland of the parasitic wasp Spalangia cameroni, and is transferred together with the venom into a fly pupa, where it manages to survive and spread.
“In most interactions between insects and the bacteria that live with them in symbiosis, the bacteria are passed from generation to generation directly through the insect’s eggs. We were surprised to find that this particular bacterium is not present in the wasp’s eggs, but uses the wasp’s venom to transfer from generation to generation. Venom is a very hostile environment for bacteria, as it is acidic and contains anti-bacterial substances— yet the bacterium manages to survive there and establish itself in the body of the young wasp,” said Dr. Sarit Rohkin Shalom, one of the research team.
Spalangia cameroni is a small parasitic wasp (about 4 mm long) that attacks fly pupae, including house fly pupae. 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 completes its development to an adult wasp.
The research was conducted in collaboration between three laboratories: the laboratory of Dr. Elad Chiel from the University of Haifa—Oranim College, led by Dr. Sarit Rohkin Shalom; the laboratory of Prof. Martin Kaltenpoth from the Max Planck Institute in Germany, led by Benni Weiss; and the laboratory of Prof. Colin Dale from the University of Utah in the USA. The study has just been published in the prestigious scientific journal Current Biology.
The researchers sought to examine how the bacterium Sodalis is transferred from generation to generation in this wasp. Their findings show that the bacterium Sodalis is located in the venom gland of the adult wasp, and when the wasp attacks a fly pupa, it is injected together 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. Thus, it is transmitted stably and cyclically to the next generation.
The research team is now exploring the mechanisms that allow the bacterium Sodalis to survive in the wasp’s venom environment and use it as a means of transmission. So far, such a route has been documented in only one other species of a parasitic wasp, but the current study suggests that it may be more common than is currently known. The researchers have also discovered that the bacterium can be transmitted through the sperm of males, albeit at a 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 Rohkin Shalom.
The researchers also discovered two other species of bacteria in the wasp Spalangia cameroni, but these are transmitted directly through the eggs, and not through the venom. It is possible that the difference lies in the length of time that the interactions between the insects and the different bacteria have developed: 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’s body, the symbiosis with the bacterium Sodalis is very young in evolutionary terms. As a result, it is still able to multiply outside the host’s cells and to exploit the venom as a vehicle of transmission.
To examine the degree of specificity of the relationship between the wasp and the bacterium, the researchers infected the wasp with a close subspecies of Sodalis, but found that it did not manage to integrate into the venom gland in sufficient quantity, and did not successfully transfer to the offspring. When injected into the fly pupa, it did not survive and did not manage to multiply there, either. This suggests that the bacterium found in the wasp has undergone specific adaptation for survival in the venom and transmission through it.
“This mechanism may be a critical stage at the beginning of the development of symbiosis between bacteria and insects,” the researchers explain. “Our findings show how bacteria can adapt and survive in non-optimal conditions, and offer a fascinating new direction for the study of the interactions between microorganisms and their hosts,” the researchers concluded.
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Preceding provided by the University of Haifa – Oranim Campus