Rickettsia influences thermotolerance in the whitefly Bemisia tabaci B biotype

The whitefly Bemisia tabaci harbors Portiera aleyrodidarum, an obligatory symbiotic bacterium, as well as several secondary symbionts, including Rickettsia, Hamiltonella, Wolbachia, Arsenophonus, Cardinium and Fritschea, the function of which is unknown. In Israel, Rickettsia is found in both the B and Q of B. tabaci biotypes, and while all other secondary symbionts are located in the bacteriomes, Rickettsia can occupy most of the body cavity of the insect. We tested whether Rickettsia influences the biology of B. tabaci and found that exposing a Rickettsia-containing population to increasing temperatures significantly increases its tolerance to heat shock that reached 40 degrees C, compared to a Rickettsia-free population. This increase in tolerance to heat shock was not associated with specific induction of heat-shock protein gene expression; however, it was associated with reduction in Rickettsia numbers as was assessed by quantitative real-time polymerase chain reaction and fluorescence in situ hybridization analyses. To assess the causes for thermotolerance when Rickettsia is reduced, we tested whether its presence is associated with the induction of genes required for thermotolerance. We found that under normal 25 degrees C rearing temperature, genes associated with response to stress such as cytoskeleton genes are induced in the Rickettsia-containing population. Thus, the presence of Rickettsia in B. tabaci under normal conditions induces the expression of genes required for thermotolerance that under high temperatures indirectly lead to this tolerance.