FIG 1.

Main interactions in the Riftia symbiosis. "HOST" refers to processes in Riftia host tissues, while "SYMBIONT" refers to processes in the bacterial endosymbiont. A plus sign indicates presumably stimulating interactions, and a minus sign indicates presumably inhibiting interactions. For example, host efforts that protect the symbiont population from oxidative stress, i.e., ROS detoxification and fermentative metabolism (on the right), can promote symbiont biomass production (+). In contrast, host immune system-related proteins and antimicrobial peptides (AMPs) may inhibit symbiont biomass production (−). Circles, where present, indicate that the respective proteins are more abundant in S-rich (energy-rich) specimens (light circles) or S-depleted (energy-limited) specimens (dark circles). The dashed arrow indicates putative transfer of small organic compounds "Milking"; see Text S1, section 3).