Since the beginning of the 20th century, different lines of fruit flies are being collected and analysed in laboratory, which allowed the identification of five strains of Wolbachia
. Nowadays, the strains that are more predominant are not the same that existed in the beginning of the past century, even though the later still endure. Luis Teixeira's team proposed to study these five Wolbachia
strains and see how they behave in terms of antiviral protection.
The researchers tested the mortality of fruit flies upon infection with two viruses, the Drosophila C virus and the Flock House virus. As expected, all flies carrying the different variants of Wolbachia
survived better than flies that did not have Wolbachia
. But the researchers found that some variants conferred higher protection to the viral infection than others. Next, the research team investigated whether the Wolbachia
variants could have a "biological cost" to the fruit flies in the absence of a viral infection. Their results showed that the variants that give stronger antiviral protection replicate more and reach higher concentrations in the fly than other Wolbachia
strains. As a result, fruit flies that carried some of the more protective Wolbachia
strains would have a shorter lifespan. These results suggest that there is a cost for the host organism when infected with bacteria that offer stronger protection against viruses.
Based on genetic studies, the research team established the phylogeny of Wolbachia
strains, and found that that the most protective strains were more closely related to the most abundant ones in the beginning of the 20th century. The strains that currently exist are less protective but more benign to their host, the fruit fly, allowing them longer lifespan. Furthermore, analysis of the DNA sequences allowed the identification of putative genes that may play a role in Wolbachia
replication and protection to viruses.
Ewa Chrostek, PhD student at Teixeira's laboratory and first author of this study, says: "We found that some of the most protective Wolbachia
variants reduce the survival of their hosts, suggesting that there may be a trade-off between the protection mediated by the symbiotic bacteria and other components of fitness. Altogether, we can understand better how Wolbachia
are evolving in nature."
Luís Teixeira adds: "Our findings can feed into the research that is currently being done to disrupt dengue transmission between people by introducing in nature mosquitoes infected with Wolbachia
. By knowing better the genetic variability of the Wolbachia
variants, a more effective strain can be used in this biocontrol strategy. Moreover, this work helps to predicted the evolution of Wolbachia
in these altered mosquito populations."