Episode Summary

Over the course of a few decades, scientists have learned how insect endosymbiont bacteria affects insect reproduction and have used this understanding to control mosquito-born diseases. Seth Bordenstein talks about his research on the insect endosymbiont, human-microbiome interactions, and how the ecosystem of a host and its microbes can be referred to as a holobiont.

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Julie's Biggest Takeaways

The holobiont concept helps scientists to study beneficial, neutral, and antagonistic relationships between hosts and their microbial ecosystems, and the holobiont changes with environmental, developmental, and genetic conditions.

Wolbachia live in 40% of arthropod species, and arthropods comprise up to 85% of all animals, meaning that Wolbachia infection affects millions of species of animals and is one of the most widespread (if not the most widespread) pandemic infections on earth.

Wolbachia is a maternally inherited endosymbiont (intracelluar symbiont) passed through the maternal germline. Wolbachia favors females and causes cytoplasmic incompatibility when the male and female arthropods are differentially infected or, in some cases, if they are infected with different bacterial strains.

By releasing mosquitos infected with Wolbachia in a concentrated area, scientists have been able to decrease and effectively eliminate local transmission of dengue, a mosquito-born viral disease, by decreasing the mosquito population.

Self-described ethnicity is a factor by which microbiomes can be categories for a sample of people from the United States. Of course, self-described ethnicity can encompass a number of factors, including genetics, data, and geographic location, and future studies will be done to find more specific factors affecting these categorizations.

The more similar 2 species are, the more similar their microbiomes are likely to be; this is the basis for the term phylosymbiosis. In a field that can be confounded by so much data, this trend has emerged as one of the most replicable ones, and future studies will look at the relationship of genetics, evolution, and microbiome.

Featured Quotes

“The holobiont is simply the ecosystem of the host and microbiome or microbial community that associates with that host, and this can include any microbes in and on that host.”

“That’s where the discussion is happening: to what extent is the holobiont a stable and evolutionariily tied-together community, versus not. My view is to have a holistic and pleuralistic of the holobiont, that there will be interactions that are transient, that come and go, and there may be interactions that are stable, and we need to figure out what that difference is and which members can be placed into which categories.”

“I don’t start with the mindset that the coevolutionary relationship but rather that it implies an ecological relationship, and potentially there are evolutionary implications within those relationships.”

“You could replace holobiont with the word ecosystem and essentially have the same meaning.”

Wolbachia is arguably the greatest pandemic in the animal world.”

"Wolbachia is a perfect example of a basic science becoming translational and applied within a few decades. Within the time of my career, I’ve seen ideas become action in how we use Wolbachia and its genetic capacities in vector control of mosquitos.”

“Students become part of our scientific community and they get that from the beginning! They are contributing to something bigger than something like a cookie-cutter lab.”

Links for This Episode

History of Microbiology Tidbit

Simeon Wolbach was born in 1880 in a small town in Nebraska, the son of Samuel Wolbach, the banker after which the town of Wolbach Nebraska is named. Isn’t it funny that the town would be named after the banker rather than the scientist? I guess scientists have to settle with organisms named in their honor. 1880 is the year James Garfield was elected U.S. President, the year the first electric streetlight was installed in Wabash, Indiana, and the year Science Magazine was first published. Did you know that Alexander Graham Bell and Thomas Edison both gave financial backing to the first Science Magazine? This was before it was associated with AAAS.

Wolbach was educated at Harvard during a time when many disease etiologies were still being discovered. In collaboration with John Todd from McGill University, he helped establish the intracellular bacterium Rickettsia prowazekii as the cause of epidemic typhus, which is transmitted by lice. Wolbach was also involved in determining the vector of Rickettsia rickettsii, which is spread by ticks and causes rocky mountain spotted fever. You can imagine after these discoveries that Wolbach might lead him to suspect other diseases were due to bacteria transmitted via insect bites. Enter Marshall Hertig, an entymology student from the University of Minnesota.

The role of insects in transmission of many infectious diseases was being established around this same time period. You may recall from an earlier History of Microbiology tidbit where we discussed yellow fever that Walter Reed is credited with firmly establishing a role for mosquitos in viral transmission; these experiments were done in the early 1900s and published in 1903. Wolbach and Hertig published their finding of rickettsia-like bacteria from the common brown mosquito Culex pipiens in 1924 - the first known publication of Wolbachia, the insect endosymbiont that lives in insect cells but is not transmitted to people and doesn’t cause disease. It wasn’t until 1936 that Hertig named the genus Wolbachia after his collaborator. In that publication, he described Wolbachia as “microorganisms having the general characteristics of the rickettsiae and exhibiting not only minute, bacterium-like forms appearing with dark-field illumination as luminous rods and points, but also enlarged forms within the body of which are contained one to several smaller individuals.”

Later, the invention of the electron microscope helped scientists survey many arthropods to establish the ubiquity of Wolbachia. Given the single species described by Hertig, Wolbachia pipientis, named after the mosquito in which it was found, combined with Seth’s inside information of nomenclature discussions at recent Wolbachia meetings, I look forward to following the taxonomy of this fascinating microorganism as it develops.

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