Direct symbiotic relationships of bacteria & animals

2 m long tubeworms (Family Pogonophora). These lack a mouth, gut or anus but contain a modified gastrointestinal tract consisiting of spongy tissue called the trophosome. Trophosome tissue contains S granules, but with large numbers ~ 109 cells/g tissue of the S-oxidising bacterium. Tubeworms are organotrophs - living off the excretory products & dead cells of the lithotrophic symbiont. S-oxidising bacterial communities have also been found in the gill tissues of giant clams & mussels. It’s possible methane-oxidising bacteria also play a role as symbionts in hydrothermal vent animals.