Animal-Microbial Symbioses

Deep-sea hydrothermal vents are dominated by symbiotic associations, which represent the majority of biomass at these habitats. Here at the Girguis lab, we study vent invertebrates (molluscs and worms) that host chemoautotrophic Proteobacteria (either intracellularly or on the outside of their bodies). In the case of intracellular symbionts, these chemosynthetic bacteria harness energy from the oxidation of the chemicals in vent fluid to fix inorganic carbon and are the primary source of nutrition for the host species. In aggregate, chemosynthetic vent communities are often more productive than rainforests and kelp beds. We study the ecological physiology of these invertebrates, utilizing shipboard experiments on live animals (HPRS) coupled to molecular analyses (e.g. qPCR, proteomics) to examine gene and protein expression in both the host animal and the bacterial symbionts. We use these experiments to replicate in situ conditions and understand how these animals interact with or tolerate the range of habitats at hydrothermal vents (e.g. temperature tolerance, utilization of different chemosynthetic substrates, etc). We also have recently developed a method of sampling and fixing animals, at the seafloor, for analysis of gene expression (iSMASH). This will allow us to link our experimental work to analyses of the animals in their natural habitat. Currently, most of our work is focused on understanding the distribution of the chemosynthetic symbioses of the Lau Basin in the variable physicochemical habitats in this area. In particular, we are focused on one genus of gastropod, Alviniconcha, which hosts two distinct Classes of Proteobacteria. We are working to understand how the differences in the physiological capacity of these two symbionts may affect the differential distribution of the Alviniconcha hosting them.

Figure 1. The Lau Basin hydrothermal vents host unique megafaunal communities, including snails and mussels that are symbiotic with chemosynthetic bacteria. These communities are known for forming “bulleyes”, with the Alviniconcha snails in the middle of the clump, followed by the Ifremeria snails and Bathymodiolus mussels. Courtesy of WHOI and J. Childress.

Figure 2. The symbioses at the Juan de Fuca ridge form some of the densest communities known in the deep sea. Ridgeia tubeworms, Paralvinella polycheates, and countless limpets grow en masse on the sides of sulfides. Courtesy of D. Kelly, UW.