SULFIDE ACQUISITION BY DEEP SEA HYDROTHERMAL VENT TUBEWORM HEMOGLOBINS
Open Access
- Author:
- Flores, Jason Francisco
- Graduate Program:
- Biology
- Degree:
- Doctor of Philosophy
- Document Type:
- Dissertation
- Date of Defense:
- March 16, 2005
- Committee Members:
- Charles Raymond Fisher Jr., Committee Chair/Co-Chair
James Harold Marden, Committee Member
Stephen Wade Schaeffer, Committee Member
Juliette Lecomte, Committee Member
A Daniel Jones, Committee Member
François Lallier, Committee Member
William Royer, Committee Member - Keywords:
- physiology
marine biology
hydrogen sulfide
respiration - Abstract:
- Changes in the environment can affect an organism in many ways. At deep-sea hydrothermal vents, organisms can be exposed to fluctuating environmental conditions. One of the best-studied animals in these environments is the tubeworm, Riftia pachyptila. This tubeworm has extracellular hemoglobins (Hbs) that bind and transport oxygen and sulfide to chemoautotrophic endosymbionts deep within the worm. The symbionts, in-turn, oxidize sulfide and provide nutrition for the worm via carbon fixation. Despite extensive studies on R. pachyptila, little is known about the ability of tubeworms to adapt to alterations in environmental conditions. The hydrothermal vent tubeworm Ridgeia piscesae is exposed to different environmental conditions along the Juan de Fuca Ridge. This study began by investigating the structure of the coelomic fluid 400-kDa Hb from R. pachyptila. From this structure it was determined that this Hb assembles into a hollow sphere, unique among Hb structures. In addition, it was shown that zinc ions, discovered during the structural analysis, are the site of sulfide binding in vestimentiferan Hbs. This contradicts a previous finding that only cysteine amino acid residues bound sulfide in these Hbs. Following this work, the structures of the Hbs from R. pachyptila were compared to the structures of the Hbs from two environmental phenotypes of R. piscesae. It was determined that the Hbs from these two species are composed of subunits with similar masses that have relatively conserved polypeptide sequences (based on cysteine content). Comparison of homologous Hbs between R. piscesae phenotypes also found no structural differences. It was previously reported that there are three distinct Hbs distributed between the vascular blood and coelomic fluid of tubeworms. The data collected for this dissertation contradict that finding and suggest that there are structurally only two Hbs in each species. In the final study, the gas transfer systems were compared between the R. piscesae phenotypes. The mass-specific surface areas and diffusion distances of the gas exchange organs are different. These differences coupled with differences in environmental gradients should lead to very different gas diffusion rates. Differences in Hb concentration and distribution between the phenotypes were also found and may indicate different gas exchange strategies between the phenotypes.