Heme proteins in sulfide-oxidizing bacteri/mollusc symbioses

Abstract

SYNOPSIS. A number of bivalve mollusc species in the families Vesicomyidae, Lucinidae and Solemyidae from sulfide-rich sediments harbor sulfide-oxidizing bacteria as intracellular symbionts in gills. Cytoplasmic hemoglobin, relatively uncommon in symbiont-free gills, is a nearly constant feature in these symbiont-harboring bivalve gills and may function in the delivery of oxygen and sulfide to ensure symbiont autotrophy and host cell respiration. However, biochemical characteristics of isolated hemoglobins from these species differ vastly. For example, within clams of the same genus, gill hemoglobin concentrations vary from micromolar to millimolar. Ligand reaction rate constants of multiple gill hemoglobins from a single species differ by three orders of magnitude. Gill hemoglobins from congeners form different derivatives in the presence of sulfide. Some hemoglobins react avidly with hydrogen sulfide while others appear refractory. This assortment of characteristics suggests that the role of hemoglobin in each symbiotic association cannot be generalized. © 1995 by the American Society of Zoologists.