Illustration of a Host-Microbial Interaction (image) California Institute of Technology Share Print E-Mail Caption Illustration: A host-microbial interaction between gut endocrine cells (right) and spore-forming gut bacteria (left) are important for fueling biosynthesis of serotonin (middle). Credit E. Hsiao/Caltech Usage Restrictions With attribution. Share Print E-Mail Disclaimer: AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert system.