Project Introduction

Because symbiotic associations between bacteria and eukaryotes are so wide-spread - from mammalian or insect digestive systems to trophosome tissues in tubeworms - it is important that the functional and evolutionary nature of symbiotic relationships be better understood. In particular, studying species diversity, dependency, host specificity, and toxicity effects within the environment helps us to understand how symbiosis has been a driver in the evolution of life on earth. For animals that live in extreme habitats, such as those containing hydrogen sulfide, bacteria in symbiotic associations with eukaryotes have provided a strategy to overcome limited metabolic capabilities or toxic concentrations. This type of symbiosis is referred to as chemosymbiosis and has been extensively documents since the late 1970’s when productive ecosystems were found at the deep-sea hydrothermal vents

In our research, we focus on chemosymbiotic relationships, and specifically on the bacteria live inside of a host and metabolize reduced compounds, such as hydrogen sulfide, and fix inorganic carbon to organic carbon that may or not be used by the host. One symbiotic association that has received attention recently is between members of the Lucinidae family of the Bivalvia and sulfur-oxidizing (thiotrophic) endosymbiotic bacteria, and chemosymbiosis in the lucinids was first reported in the 1980’s.

Our ongoing research has investigated the genetic diversity and ecology of a variety of lucinid hosts and their bacterial endosymbionts from spatially separated locations in the Gulf of Mexico, as well as the bacterial diversity of the host habitat (marine siliciclastic sediments). Most of the symbionts belonged the the Gammaproteobacteria, a class within the Proteobacteria. The results of the study thus far (as part of the MS thesis of Green-Garcia), provide unique genetic evidence for bacterial endosymbiont diversity, as well as indicate that geography may play a role in the diversity of the bacteria-lucinid association.

Dissecting lucinids to retrieve gills containing bacteria.
Photo by A.S. Engel.

Dissecting lucinids to retrieve gills containing bacteria.
Photo by A.S. Engel.

Project Goals
There is still much to do on this project, including collecting more lucinid taxa from geographically separated sites, as well as lucinids from carbonate-hosted depositional settings (e.g., The Bahamas).  The 16S rRNA gene sequences of bacteria from numerous hosts have been retrieved, but a broader look at functional activities of the bacteria is needed (e.g., doing functional gene surveys, as well as fluorescence in situ hybridization-microautoradiography experiments).

Inquire with Dr. Engel if you are interested in the work.

Project Collaborators:
Laurie Anderson, LSU
Huiming Bao, LSU
Audrey Aronowsky (post-doc, formerly at LSU)
Angela Green-Garica (graduate student)
Yongbo Peng (graduate student)
Maureen Thiessen (undergraduate student)
Kelley Gwin (undergraduate student)

Sieving sediments from marine seagrass beds to collect living lucinids.
Photo by A.S. Engel.


Sampling pore water fluids in seagrass beds.
Photo by L. Anderson.