The Science of The Superorganism: Host-Microbiota Specificity, Again

What determines the constituents and abundance of microbes in a host? 

A critical question emerging in the science of the Superorganism (our genes + microbial symbionts) is how exactly does the microbial symbiont community inside us assemble? Is it random? Do we just acquire the bacteria that are around us when we're born? Does our diet affect which bacteria thrive in our guts? Do our genes interact with the admixture of microbes in the environment to select for specific ones that confer beneficial traits?

Numerous studies show the influence of diet on the assemblage of the microbial community. But emerging studies in the past year, which have received less attention, indicate the host selects for specific species of bacteria as well. Here are three highlight stories:

1. Hawlena et al (2012) show that in fleas and ticks, the composition of the microbial symbiont community is not determined by their vertebrate host (rodents) or environment, but by their arthropod host. Specifically, ticks have different communities of microbes than fleas, and species of ticks share more similar microbial communities than species of fleas. Other factors such as rodent host did not matter as much.

2. Salem et al (2012) show in firebugs that the "fitness of symbiont deprived bugs could be completely restored by re-infection with the original microbiota, while reciprocal cross-infections of microbial communities across both pyrrhocorid species only partically rescued fitness, demonstrating a high degree of host-symbiont specificity" In particular, survivorship decreases and nymphal development time to adulthood increases in aposymbiotic and cross-infected species, but not control or re-inoculated species. Even mating frequency is reduced. This study has a really beautiful set of functional data.

3. Engel and Moran (2013) describe a specific and stable microbial community of honey bees, suggesting long-term coevolution between bee-specific bacteria and bees.

If anyone has any important studies to highlight on this topic, please let me know so I can post them.

Note: we also found species-specific microbiotas that changed in constituents and abundance in parallel with the speciation events of their Nasonia wasp hosts. Related blog posts on this work:

• The story behind Speciation by Symbiosis (April 26, 2012)
• Is the microbiome part of the organism or the environment? (May 11, 2012)
• Is the microbiota species specific? (June 23, 2012)
• ASM's Small Things Considered Spotlights Our Article (August 16, 2012)