Despite human caffeine addictions, only one insect, the coffee berry borer (Hypothenemus hampei), can subsist solely on coffee. Spending most of its life inside green coffee beans, this tiny beetle can survive on levels of caffeine that are extremely toxic to most insects. How does this coffee pest manage a habit that ravages coffee crop production?

Microbial ecologist Javier A. Ceja-Navarro of the Lawrence Berkeley National Laboratory and nine colleagues suspected bacteria living in H. hampei's gut might be involved. First, the researchers measured how much caffeine passed through the digestive tracts of laboratory-raised H. hampei when fed a coffee bean diet. Next, the team added antibiotics to the beetles' diets for four weeks, wiping out any gut microbes, and then re-measured the caffeine excreted. They also identified which bacterial species inhabited beetles from seven coffee-producing regions: Mexico, Guatemala, Hawaii, Puerto Rico, Indonesia, Kenya, and India.

Finding a core group of microbes in H. hampei across all locations, researchers narrowed down which of those bacterial species could survive with only caffeine for food. They also screened the bacteria for a gene known to be involved in metabolizing caffeine, and determined that only Pseudomonas fulva possessed this useful gene. Finally, the team introduced P. fulva into the diet of the lab-reared H. hampei, whose guts were previously sterilized by antibiotics and, after a week, remeasured whether they could break down caffeine. 

With their normal gut bacteria, H. hampei could metabolize almost all the caffeine consumed, but after antibiotic treatment, caffeine passed through untouched. Adding P. fulva to their diet, however, allowed the beetles to break down caffeine once again, establishing a key role for gut bacteria. This knowledge could lead to new approaches for controlling this destructive agricultural pest. (Nature Communications)