Metabolic provisioning of Drosophila by Wolbachia: how a classic reproductive parasite might also act as a mutualist
Wolbachia are maternally transmitted intracellular bacteria that infect a broad range of invertebrate species. Wolbachia that infect insects modify their host's reproduction to increase the number of infected females within a population, and are considered parasitic. Wolbachia that infect filarial nematodes behave as obligate mutualists, as removal of the endosymbiont results in death of the worm. As a number of insect infecting Wolbachia strains do not appear to induce any form of reproductive parasitism, yet are able to exist at high frequency in host populations, it has been postulated that they might confer a fitness advantage to the insect. However despite considerable searching no evidence has been found for any fitness benefit for Wolbachia infected Drosophila. Analysis of recently completed Wolbachia genome sequences revealed that insect Wolbachia are capable of synthesising several metabolic co-factors and vitamins. As such they may be able to provision hosts and positively influence fitness of infected insects. We tested this hypothesis by rearing D. melanogaster on different nutritionally deficient diets and in some cases found significant positive fitness effects in the presence of the Wolbachia infection. These effects may help explain an unresolved paradox in Wolbachia biology.