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The Wolbachia "holy grail"

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The once-obscure alpha-proteobacterium Wolbachia pipientis, was catapulted into medical relevance by the discovery that it inhibits the replication of RNA viruses.  However, it was first discovered for its odd quirk of manipulating insect reproduction. That's right, Wolbachia were called "reproductive parasites" and for a long time, no fitness benefit was attributed to them.  These intracellular masters do things like kill male offspring, feminize male offspring, induce parthenogenesis, and the most common phenotype, sperm-egg incompatibility (also known by its more complicated name: cytoplasmic incompatibility or CI) (Figure 1).  



Figure 1. Modified from Werren et al., 2008.  Wolbachia cause four distinct reproductive phenotypes in a range of arthropod orders (top). 

The mechanisms behind CI - meaning how does Wolbachia induce it - have been a mystery for some time.  When you make a cross between infected males and uninfected Nasonia females, unviable embryos result from …