Widespread prevalence of wolbachia in laboratory stocks and the implications for Drosophila research

Abstract

Wolbachia is an intracellular microbe harbored by a wide variety of arthropods (including Drosophila) and filarial nematodes. Employing several different strategies including male killing, induced parthenogenesis, cytoplasmic incompatibility, and feminization, and acting by as-yet-unknown mechanisms, Wolbachia alters host reproduction to increase its representation within a population. Wolbachia is closely associated with gametic incompatibility but also interacts with Drosophila in other, little understood ways. We report here significant and widespread infection of Wolbachia within laboratory stocks and its real and potential impact on Drosophila research. We describe the results of a survey indicating that approximately 30% of stocks currently housed at the Bloomington Drosophila Stock Center are infected with Wolbachia. Cells of both reproductive tissues and numerous somatic organs harbor Wolbachia and display considerable variation in infection levels within and between both tissue types. These results are discussed from the perspective of Wolbachia's potential confounding effects on both host fitness and phenotypic analyses. In addition to this cautionary message, the infection status of stock centers may provide further opportunities to study the genetic basis of host/symbiosis.

Figure 1.—

Cytoplasmic incompatibility. There are four different mating combinations between infected and uninfected males and females. Infected females (blue) produce infected offspring that develop normally regardless of paternal infection status. Uninfected males mate successfully with both infected and uninfected females. Infected males (yellow) with Wolbachia-modified sperm mated to uninfected females produce some embryos with early embryonic lethality, characterized by defects in early mitotic divisions (CI, lower left). In late telophase, nuclei (arrowheads) are abnormal and do not properly separate during anaphase/telophase. These defects are rescued when mated to infected females (rescue, lower right). Wolbachia are seen as small punctate dots with high concentrations associated with astral microtubules. Red, DNA; green, tubulin. Bar, 10 μm.

Figure 2.—

Wolbachia infection in D. melanogaster stocks. (A) Percentage of infected stocks categorized by general class of genotype. (B) Wolbachia infection in various P-element mutagenesis screens.

Figure 3.—

Wolbachia in different organs from a wild-type (BDSC no. 3839) D. melanogaster third instar larva (A–G) and pupa (H and I). (A) Nerves, (B) Malpighian tubules, (C) salivary gland, (D) trachea, (E) haltare imaginal disc, (F) fat bodies, (G) proventriculus, (H) eye, (I) ovary. Red, DNA; green/yellow, Wolbachia. Bars, 10 μm.

Figure 4.—

Wolbachia in the nuclear end of sperm cysts. Elongated cysts removed from testes from three different Wolbachia-infected lines and stained with propidium iodide (staining both Drosophila and Wolbachia DNA). Variation is seen in Wolbachia (w) distribution within developing sperm cysts adjacent to spermatid nuclei (n). (A) BDSC no. 10030, w¹¹¹⁸ P{EP}sd EP¹⁰⁸⁸. (B) BDSC no. 97, Df(2L)JS32, dpp^d-ho/CyO, P{sevRas1.V12}FK1. (C) BDSC no. 1128, Df(2L)GpdhA/CyO.