On November 12th the topic will be microbial manipulation of host behavior. Can this be an important feature of human health and behavior?
For an introduction, read this Berkeley Science Review.
I am writing a hypothesis paper with Athena Aktipis and Carlo Maley entitled: “Could microbial manipulators be the culprits behind unhealthy eating” The abstract is here:
Two of the greatest unsolved mysteries of our time are (1) why obesity has reached epidemic proportions in the western world, and (2) why we crave foods that are so bad for us. Here we suggest that solving these mysteries may require a closer examination of the influence that gut microbes may have on our physiology and behavior. Unhealthy food preferences, according to conventional wisdom, have evolved because high-fat, calorie dense, and salty foods were much more limited in the environment of our distant ancestors. However, some evidence suggests an alternative explanation: our cravings and aversions may serve the evolutionary interests of our gastrointestinal microbiota. Here we investigate whether our gut microbes have the means, motives, and opportunity to control our eating behavior. Gut microbiota have direct access to the blood stream (via absorption of small molecules through our intestines) and nervous system (via enteric nerves), giving them the ability to manipulate us to consume nutrients that promote their survival and proliferation. Many examples exist of microbes manipulating the behavior of host organisms; we hypothesize that microbes influence eating behavior, in part by rewarding us for eating the foods upon which they depend, or by making us feel bad if we do not provide a constant supply of their growth-limiting nutrients. In other words, the problems of overeating, obesity and diabetes may lie less in our genes or our brains, and more in the composition of our guts. Here we consider the interplay of competing fitness interests of host and microbiota and review the evidence supporting our hunch that microbial puppetmasters may be the culprits behind unhealthy eating behavior and the obesity epidemic.
I can email students a draft of the revised document but cannot post it here (it is not a required reading). A similar argument has been published by Lyte (2013) above, which is a required reading.
Writing assignment (1 page max): Do you think it is likely that our food cravings are driven by the evolutionary interests of our gut microbiota? Why or why not? Are there other explanations for why we crave fatty, sugary, and salty foods?
Optional extra credit: (3/4 page max):
Conditional virulence expression is common among bacteria inhabiting the human gut. The system of intra- and inter-specific communication known as quorum sensing uses detection of signal molecules, including nutrients, to regulate virulence and growth. Carbon growth substrates (e.g., glucose) and critical micronutrients (e.g., iron) have key signaling roles that regulate virulence-related factors. Many pathogens are sensitive to the availability of iron, activating virulence when iron is limited. The same is true for zinc and manganese, and glucose. “Nutrient virulence” is a newly coined term to describe the pathogen strategy of harnessing or destroying host cellular machinery to exploit the nutrients held within. The concept of nutrient virulence suggests that when gut microbes are starved for nutrients needed for growth, they will attack host cells to gain access to those resources. Drawing on the Ponton article, do you think that facultative virulence by gut microbes could affect our food choices?