Symbiotic ammonia-oxidizing archaea in marine sponges are not strict specialists, but true "flexitarians": A team led by microbiologists Bettina Glasl and Katharina Kitzinger from the University of Vienna, in collaboration with partners from Australia, has shown that these microbes dine not only on ammonia but also on amino acids such as valine, leucine, and isoleucine - and presumably do that to communicate with their animal host. The findings shed new light on one of the oldest animal-microbe symbiotic relationships on Earth and point to a previously underestimated role played by archaea. The study was published in the prestigious journal Science Advances.