Mapping Wolbachia distributions in the adult Drosophila brain.

The maternally inherited bacterium Wolbachia infects the germline of most arthropod species. Using Drosophila simulans and D. melanogaster, we demonstrate that localization of Wolbachia to the fat bodies and adult brain is likely also a conserved feature of Wolbachia infection. Examination of three Wolbachia strains (WMel , WRiv , WPop ) revealed that the bacteria preferentially concentrate in the central brain with low titres in the optic lobes. Distribution within regions of the central brain is largely determined by the Wolbachia strain, while the titre is influenced by both, the host species and the bacteria strain. In neurons of the central brain and ventral nerve cord, Wolbachia preferentially localizes to the neuronal cell bodies but not to axons. All examined Wolbachia strains are present intracellularly or in extracellular clusters, with the pathogenic WPop strain exhibiting the largest and most abundant clusters. We also discovered that 16 of 40 lines from the Drosophila Genetic Reference Panel are Wolbachia infected. Direct comparison of Wolbachia infected and cured lines from this panel reveals that differences in physiological traits (chill coma recovery, starvation, longevity) are partially due to host line influences. In addition, a tetracycline-induced increase in Drosophila longevity was detected many generations after treatment.

Rapid fluorescence-based screening for Wolbachia endosymbionts in Drosophila germ line and somatic tissues.

Wolbachia is a globally distributed bacterial endosymbiont present in arthropods and nematodes. The advent of sensitive PCR-based approaches has greatly facilitated the identification of Wolbachia-infected individuals and analysis of population infection levels. Here, a complementary visual fluorescence-based Wolbachia screening approach is described. Through the use of the fluorescent dye Syto-11, Wolbachia can be efficiently detected in various Drosophila tissues, including ovaries. Syto-11 also stains Wolbachia in other insects. Because Wolbachia is inherited through the maternal germ line, bacteria reside in the ovaries of flies in infected populations. An advantage of this staining approach is that it informs about Wolbachia titer as well as its tissue and cellular distribution. Using this method, the infection status of insect populations in two central California locations was determined, and variants with unusually low or high Wolbachia titers were isolated. In addition, a variant with ovarioles containing both infected and uninfected egg chambers was identified. Syto-11 staining of Cardinium- and Spiroplasma-infected insects was also analyzed.