Using the Wolbachia Bacterial Symbiont to Teach Inquiry-Based Science: A High School Laboratory Series
Bordenstein, Seth R., Brothers, Christine, Wolfe, George, Bahr, Michele, Minckley, Robert L., Clark, Michael E., Wernegreen, Jennifer J., Bordenstein, Sarah R., Reznikoff, William S., Werren, John H., The American Biology Teacher
Humans consist of approximately 10% human cells and 90% prokaryotic cells, yet the idea of studying the varied relationships between eukaryotic hosts and prokaryotic symbionts is largely ignored in introductory biology classes. "Discover the Microbes Within! The Wolbachia Project" is an innovative lab series that gives students the opportunity to make original scientific discoveries about invertebrate endosymbionts while learning integrative approaches in biodiversity, evolution, cell biology, molecular biology, and bioinformatics. The project utilizes the widespread symbiont Wolbachia, inherited intracellular bacteria that live within the cells of the reproductive tracts of ~66% of arthropod species (Hilgenboecker et al., 2008). One arthropod subgroup, the insects, comprise ~85% of all animal species, which makes Wolbachia perhaps the most common bacterial endosymbiont in the biosphere. Estimates place these bacteria in millions of arthropod species.
Wolbachia are primarily passed from mother to offspring through the cytoplasm of the egg (Figure 1) but can also be horizontally transmitted between arthropods. Wolbachia are commonly referred to as "reproductive parasites" because they manipulate sexual reproduction in their hosts in four ways (Werren et al., 2008). Wolbachia can kill infected males outright (male killing), cause male offspring to develop into females (feminization), cause females to reproduce asexually or clonally (parthenogenesis), or kill the offspring of an uninfected female when its mate is infected (cytoplasmic incompatibility). All these strategies increase the number of Wolbachia-infected females, thereby increasing parasite transmission. Wolbachia was first discovered in the 1920s, but its significance to insect speciation (Bordenstein, 2003), evolution, and ecology (Stouthamer et al., 1999; Werren et al., 2008) and to human health (Taylor, 2002; Sinkins & Gould, 2006; McMeniman et al., 2009) was little appreciated until recently.
In addition to insects, Wolbachia are also known to infect filarial nematodes, terrestrial crustaceans (isopods), mites, scorpions, and spiders. Wolbachia infections play an important role in filarial nematodes that cause the human diseases onchocerciasis ("river blindness") and elephantiasis (Taylor et al., 2005). An electron micrograph of Wolbachia in filarial nematodes is shown in Figure 2. Treatment with antibiotics eliminates the Wolbachia from these disease-causing worms, thereby killing or sterilizing the worms. Wolbachia is also a potential biological control agent or genetic vector for spreading desirable genetic modifications in insects (Sinkins & Gould, 2006; McMeniman et al., 2009).
Wolbachia biology is poised to initiate curiosity and inquiry in the classroom. The inquiry for this project can be introduced in many ways, by asking questions such as "Why would organisms want to live inside the cells of another? What mechanisms have the bacteria evolved to spread through host insects? What can we learn from Wolbachia biology to control the spread of insect-borne West Nile virus or agricultural pests? What does this symbiosis tell us about the nature of our own cells?" All these questions have exciting answers from this single system. Notably, the Wolbachia scientific community isn't big enough by itself to adequately sample the world's arthropod and nematode populations for this infection. Students are potentially the biggest assets in helping scientists study these important topics.
Discover the Microbes Within! The Wolbachia Project
The lab exercises, originally conceived by John H. Werren, were developed in 2004 as part of a National Science Foundation Frontiers in Integrative Biological Research (FIBR) award. The goals of this award were to integrate genetic, cell biology, ecological, and environmental aspects of Wolbachia biology. In this same spirit, a series of integrated laboratory exercises were designed to use Wolbachia to teach students about biodiversity, ecology, entomology, genetics, cell biology, molecular biology, and bioinformatics (Figure 3). …