| Summary: | <p>Abstract</p> <p>Background</p> <p>In recent years, acetic acid bacteria have been shown to be frequently associated with insects, but knowledge on their biological role in the arthropod host is limited. The discovery that acetic acid bacteria of the genus <it>Asaia</it> are a main component of the microbiota of <it>Anopheles stephensi</it> makes this mosquito a useful model for studies on this novel group of symbionts. Here we present experimental results that provide a first evidence for a beneficial role of <it>Asaia</it> in <it>An. stephensi</it>.</p> <p>Results</p> <p>Larvae of <it>An. stephensi</it> at different stages were treated with rifampicin, an antibiotic effective on wild-type <it>Asaia</it> spp., and the effects on the larval development were evaluated. Larvae treated with the antibiotic showed a delay in the development and an asynchrony in the appearance of later instars. In larvae treated with rifampicin, but supplemented with a rifampicin-resistant mutant strain of <it>Asaia</it>, larval development was comparable to that of control larvae not exposed to the antibiotic. Analysis of the bacterial diversity of the three mosquito populations confirmed that the level of <it>Asaia</it> was strongly decreased in the antibiotic-treated larvae, since the symbiont was not detectable by PCR-DGGE (denaturing gradient gel electrophoresis), while <it>Asaia</it> was consistently found in insects supplemented with rifampicin plus the antibiotic-resistant mutant in the diet, and in those not exposed to the antibiotic.</p> <p>Conclusions</p> <p>The results here reported indicate that <it>Asaia</it> symbionts play a beneficial role in the normal development of <it>An. stephensi</it> larvae.</p>
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