Tubeworms can grow fast and large?up to 6 feet tall?near hydrothermal vents on the seafloor. They do it with a lot of help from bacteria living inside of them. The tubeworms supply hydrogen sulfide (from vent fluids) and oxygen and carbon dioxide (from seawater) to the bacteria, which use them to produce nutrients for the tubeworms. (© Woods Hole Oceanographic Institution)
Cross sections of the tubeworm Riftia pachyptila. (Courtesy of Enduring Resources for Earth Science Education)
Scientists discovered that endosymbiotic bacteria living inside tubeworms are capable of using two fundamentally different means to generate organic carbon. The first is the Calvin Cycle (above), in which carbon molecules from CO2 are fixed into glucose (C6H12O2. The Calvin cycle works when there is plenty of oxygen around, but requires substantially more energy than the other method the bacteria use: the rTCA cycle (below). (Courtesy of Thinkquest.org)
The endosymbiotic bacateria inside tubeworms can also use another metabolic pathway to produce organic carbon: the reductive tricarboxylic acid (rTCA)cycle. This cycle requires less energy, but not does work in high-oxygen conditions. The capability to use both methods gives the bacteria (and the tubeworms that depend on them) flexibilty to survive under changing environmental conditions. (Courtesy of Stefan Sievert, Woods Hole Oceanographic Institution)
Stefan Sievert, a microbiologist from Woods Hole Oceanographic Institution, was part of a scientific team that helped show that endosymbiotic bacteria living inside tubeworms can use two fundamentally metabolic pathways to produce organic carbon?the first organism with that capability ever discovered.