10/28/2005

Modus operandi of parasitic bacterium revealed

By Branwyn Stewart Wagman, QB3 UC Santa Cruz

The image depicts maternal transmission of Wolbachia. Within the Drosophila female germ line, the intracellular a-proteobacteria Wolbachia (red) accumulates in the cell that will form the fruit fly egg and embryo and is thereby transmitted to the next host generation. Green indicates germ line, and blue indicates DNA. (Image by Horacio M. Frydman and Eric Wieschaus)

The cover of the October issue of PLoS Pathogens (Vol. 1, Issue 2) features research by MCD biologist Bill Sullivan and colleagues on Wolbachia, a parasitic bacterium that lives inside the cells of many insects. Wolbachia travel from host to host on the female germ line. Since they reside in the host cell’s cytoplasm they cannot be transmitted by sperm.

Sullivan, his graduate students, Patrick Ferree and Jian Cao, and collaborators from Princeton University found that in the fruit fly Drosophila, Wolbachia ensure their eventual transmission early in the host’s development cycle by establishing an early infection in the cell destined to become the oocyte.

During mid-oogenesis, the bacteria accumulate in the anterior portion of the oocyte next to the nuclear envelope. This location may serve to keep them out of the way so that they do not disrupt proper oocyte development. While there, they replicate rapidly.

Ferree explained, "The success of Wolbachia in nature hinges on the success of its host.  Wolbachia walks a fine line between using host cellular machinery to become efficiently transmitted while not interfering with any of a number of processes that are critical for proper embryonic development. This has likely occurred through fine tuning over evolutionary time."

Next, they dissociate from the nuclear membrane and disperse throughout the cell. They appear to move about by commandeering the microtubules and motor proteins in the host cell’s transport system.

Because these studies elucidate host cell function as well, they may ultimately lead to a greater understanding of basic host cellular and developmental processes.