Gut-associated microbial symbionts of the marsh fiddler crab, Uca pugnax

Lara Gulmann, Ph.D., 2004
Lauren Mullineaux, Advisor

Digestive associations between marine invertebrates and resident (attached) microbial communities may play a critical role in host physiology and involve previously unidentified microbial species. The goal of this thesis was to characterize the ecology and genetic diversity of resident gut microbes to advance our understanding of their interactions with their host, the marsh fiddler crab, Uca pugnax. The greatest abundances of both bacteria and protists were documented in the host stomach and hindgut. For these sections, I have described morphologies, measured abundances and characterized the genetic diversity of resident microbes. Presence and abundance of Eccrinales protists depends on host molt stage as all eccrinid biomass is shed with the host's molt. Bacterial diversity patterns seem to be comparable among individuals and over time, as assessed by denaturing gradient gel electrophoresis (DGGE). Community composition, however, does differ between stomach and hindgut populations, as resolved by DGGE and clone libraries of the 16S rRNA gene. Many recovered clones were most closely related to other symbiotic or gut-associated bacteria. Functionally, resident bacteria, particularly in the hindgut, may contribute to total enzyme activity in the gut of their host.